Choosing and Using Fertilizers in the Yard and Garden [audio]

Emma and Nate are joined by researcher Becky Sideman to talk fertilizers for the yard and garden, covering how to choose the appropriate fertilizer, and how and when to apply them. They also take on common misconceptions and give practical advice you can

Gloved hand with fertilizer and a potted plant

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Plants need air, water and sunlight, but require sources of essential nutrients too. Fertile soil rich in organic matter provides nutrients to be sure, but fertilizer is typically needed to grow vigorous, healthy plants. Organic or not, slow release or fast acting, specialty products or versatile mainstays – we face a lot of options when choosing fertilizers. And that doesn’t even begin to cover when and how to use the fertilizer for the wide diversity of plants you’re growing. 

In this episode of Granite State Gardening, UNH Extension’s Emma Erler and Nate Bernitz are joined by Becky Sideman to share proven tips and solutions for using fertilizer to grow healthy and productive plants in the garden and landscape. The conversation brings up topics and questions bound to get gardeners of all experience levels thinking about fertilizing plants in the yard and garden in new ways. 


Featured Question: Should I use fertilizer spikes or a granular fertilizer for my trees and shrubs? 

·         Featured Plant: Bee Balm (Monarda fistulosa)

·         Closing Tip:   New Hampshire’s Turf Fertilizer Law


          Fertilizing vegetable gardens 

·         Fertilizing fruit trees

·         Fertilizing trees and shrubs

·         New Hampshire’s turf fertilizer law

·         Soil testing

·         Spring Webinar Series

UNH Cooperative Extension’s Vegetable & Fruit team, together with a group of undergraduate and graduate students at the University of New Hampshire, conduct research on vegetable and fruit crops. While the team does much of their work at theNH Agricultural Experiment Station in Durham, NH, they are located throughout NH and their research project topics are driven by the needs of NH growers. The team believes that using effective growing practices for our region (including new varieties, new crops, and season extension strategies) can help farmers diversify, improve yields, and improve crop quality. Many of their integrated research and extension projects focus on high-value specialty crop production systems and methods of extending the growing season (e.g. season extension). They offer an up-to-the-minute snapshot of what we're up to on Instagram at unh_sidemanlab.

Connect with us at @askunhextension on FacebookInstagram and Twitter and subscribe to the monthly Granite State Gardening newsletter.

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Transcript by

Nate Bernitz  0:00  
Welcome to the Granite State gardening podcast produced by UNH Cooperative Extension. Today we're releasing part two of a two part conversation on amending and fertilizing plants in the Yard and Garden. Part one focused on amendments whereas Part two focuses on fertilization. In this episode, we'll tackle common misconceptions, practical knowledge about how to choose the right fertilizer, and how and when to fertilize all the plants in your yard, garden, and orchard.

Greetings Granite State gardeners I'm Nate Bernitz, Public Engagement Manager for UNH Extension joined by horticulturist and UNH extension field specialist Emma Erler, as well as Becky Sideman, a repeat guest on Granite State Gardening. Becky wears multiple hats at the University of New Hampshire. She's a sustainable horticulture state specialist for extension, a professor of Sustainable Agriculture and Food Systems, a coordinator of that undergraduate program and a researcher at the New Hampshire Agricultural Experiment Station. Emma, generally speaking, what do you view as the role of fertilization? What do you see from gardeners who maybe don't fertilize or just don't put a lot of thought into fertilization, let's establish up at the top why fertilization is important.

Emma Erler  1:31  
I guess I'll start by saying that fertilizing is important because it's providing a source of essential nutrients that that plants really need to grow normally and be healthy. A lot of times, nutrients that are are supplied by the soil, or decomposing organic matter, may not be in adequate quantities for optimal plant growth. So adding some fertilizer to your soil can actually optimize what you're getting out of your garden. And that's give obviously, is really important. If you're not fertilizing at all, it might be okay, depending on on what you're trying to do and what's going on with your soil, you know, perhaps you're adding other amendments, you're adding compost, or you're adding manure, and you're getting some good nutrients from that. If you're not doing that, so you're basically just doing nothing to your soil, either plants just aren't going to grow very well, or they're going to grow very, very slowly.

Nate Bernitz  2:39  
In part one of this conversation, I asked you, Becky, what is a soil amendment? And so I'll ask the flip side of that, what is a fertilizer? Is it that its primary role is adding macronutrients versus a soil amendment where the primary role is improving the soil in some other way? Is that the right distinction? And where do micronutrients come into play? Are you getting those from both fertilizers and soil amendments?

Becky Sideman  3:07  
That's a great question. Yes, you've got hit the nail on the head in terms of the definition. So fertilizers are providing those macronutrients that plants need in the largest quantities. Depending on the fertilizer source that you choose, and there are many, many, many choices, you may be produce- you may be adding micronutrients as well or you may not be. There are fertilizers that are pretty much sole elements like nitrogen, phosphorus, potassium, magnesium. There are also blended complete fertilizers that contain all the macronutrients and all the micronutrients. And of course, if we get into the topic of conventional versus organic, those organic fertilizers are kind of by definition because they come from plants or animals, contain the whole spectrum of macro and micronutrients. So you can have any of a number of essential elements in a fertilizer that plants are going to need to grow

Nate Bernitz  4:17  
in a vegetable garden, for someone who either isn't fertilizing or not fertilizing at the correct ratio, what might you expect to see? What are going to be those signs of macro nutrient deficiencies?

Becky Sideman  4:34  
Probably the most common macro nutrient deficiency that you would see is pale or yellow plants, overall stunting and not very vigorous looking plants and also pale and vigorous looking weeds. Not just your plants, but not the ones you planted, but all of them. So that would indicate insufficient nitrogen or possibly insufficient, all nutrients. It's certainly possible early in the season to see some purpling of plants because of phosphorus deficiency. I would say that's not super super common, especially once the soil warms up. And you can certainly there are a whole range of symptoms that you could pick out that identify, that are associated with, missing particular elements. But those are quite rare to see in the context of a farm or garden. Because in a farm or garden, a soil contains, that has any organic matter at all, has some of all of these nutrients. So it's pretty rare to see very stark examples of clear nutrient deficiencies. The most common thing is just overall poor lack of growth.

Emma Erler  6:03  
And I'll add too when you're seeing potentially some some symptoms that look like nutrient deficiency, It may not be because there's a lack of nutrients in the soil. In the last episode, we spent a fair amount of time talking about pH. So if the pH of your soil isn't appropriate for what you're trying to grow, those nutrients might be unavailable to the plant, so the plant's exhibiting some nutrient stress symptoms, or where it's or some deficiency symptoms. So that's, that's something to explore as well, before you automatically put more fertilizer onto your garden.

Nate Bernitz  6:42  
Are we considering, I don't know something like epsom salts, which is not a source of a macronutrient, but the source of a very important secondary nutrient, is that considered a fertilizer? And how common are deficiencies of say, magnesium or calcium? And what might that look like? Because I certainly hear from people kind of frequently, especially over the summer, who are really concerned about some kind of calcium or magnesium deficiency. Maybe it's something like blossom end rot or something like that.

Becky Sideman  7:18  
I would say that, for as far as magnesium, epsom salts are fertilizer, so yes, they're providing magnesium and sulfur, which are both, as you pointed out, important secondary nutrients for plants. I would say that it's most common, it's quite common actually to see symptoms of magnesium deficiency on the older leaves of tomato plants. Whether or not this is a problem is a debatable subject, because what happens as the plants grow and they set fruit and try to ripen those fruit is that those elements are are kind of allocated to the fruit. And so it's natural that they should leave the leaves. And so symptoms of magnesium deficiency is not, I wouldn't say necessarily a problematic, a problematic thing. That said, certain crops do use a lot of magnesium. And so replacing that as you harvest those crops off is is a piece of, is a piece of replacing those nutrients that is worth paying attention to. The calcium one is a really big and interesting question. And while it's true, lots of lots of vegetables get blossom end rot, cucumbers, zucchini, summer squash, tomatoes, peppers, you know, we can we see a lot of calcium disorders in the form of blossom end rot. But what's interesting about that is that even though it's a calcium disorder, there's not calcium getting to those growing points of the fruit. It isn't due to lack of calcium, and adding more calcium does not help. It's due to uneven moisture supply and moisture not being able to get taken up into the plant to keep that calcium moving to those fruit growing points. And often it's not even poor irrigation. often it happens like early in the season when the rate of growth is just so fast, and the plants can't keep up and it's the first hot sunny day in June and the leaves wilt a little bit, and then you'll have a little bit of blossom end rot. So adding calcium is often not the solution to this calcium disorder. It's merely managing water so that they have consistent access to water so that nutrients can move through their system better.

Nate Bernitz  9:54  
And just to be clear, if you're adding a complete fertilizer and I guess fertilizers don't typically say they're complete, but a fertilizer that has nitrogen, phosphorus, potassium, we're estimating that that's a complete fertilizer, or I guess that's a question. But are you also assuming that there is magnesium and calcium and perhaps other things in that fertilizer?

Becky Sideman  10:20  
The fertilizer label will tell you what's in there. And so it will tell you, all of the constituents and you can look to see whether it contains all the micronutrients and magnesium, calcium and sulfur in addition to those three macronutrients the nitrogen, phosphorus and potassium. So it will tell you that. And honestly, they they come in all types. And so you can get fully complete with micronutrients, fertilizers, as well as ones that do not have all of those micronutrients,

Nate Bernitz  11:01  
which is not necessarily true for the manure from, the, your farmer neighbor down the road, but it's true for any fertilizer you're purchasing at the store.

Emma Erler  11:10  
Yeah, all fertilizers have what's called a guaranteed analysis. So that's, and that's going to be printed on the packaging somewhere. So you're going to know exactly what's in there by percentage.

Nate Bernitz  11:22  
So I thought we could spend a couple minutes talking about timing for fertilizer applications. And do you think it's important to kind of go almost sort of vegetable garden fruits, lawn, etc? Like, is it important to talk about those separately when it comes to timing? Or is the timing pretty much the same? No matter what you're growing?

Emma Erler  11:47  
I think it's probably worth talking about them separately. Yeah, the way you treat a lawn is going to be very different from the way you're treating your vegetable garden.

Nate Bernitz  11:55  
We'll say more about that. How do you time fertilizer applications in a lawn?

Emma Erler  11:59  
Well, one of the things you got to consider is, you know, when the crop you're growing is actually going to be using those nutrients. If you're growing an annual crop, that plant is going to be using a lot of those nutrients early in the season, when it's putting on all of its growth, so early in the summer, primarily before it's started flowering or fruiting. If you're talking about a plant that's perennial, so it's growing for three or more years, that plant is potentially going to be taking up nutrients, right up through the fall. So for a lawn, for example, people will often fertilize their lawn in early fall, ideally, so let's say right after Labor Day, because that plant is going to be taking up some of those nutrients and using it to grow a healthier root system, for example. Versus if you're growing an annual flower, or an annual vegetable, it really doesn't make sense to be putting fertilizer down in the fall, because those plants have already lived their lifespan, and they're not going to be using those nutrients, and they're just going to go to waste. They're probably going to leach out of the soil before you have something planted in that spot again, the next year. So that's that's really how I'm thinking about it, you know, when when are these nutrients going to be put to maximum use by the plant, so I'm going to be the least wasteful, possible. Not putting nutrients down when plants aren't using them.

Nate Bernitz  13:29  
And understanding that it may depend on the product you're using for a vegetable garden, how do you think about timing for those applications? And how does the product you're using influence that if at all?

Becky Sideman  13:42  
So as Emma said, you really want the materials to be there when the plants are doing the majority of their growing. And so for many members of the vegetable garden, this means that you can go ahead and apply most of the nutrients that are needed or all into the soil before you plant. And I generally suggest folks do that on a bed by bed by bed basis or row by row basis as they plant so it's just to time it so that right when the crop is going in. Now, realistically, for plants that will have a long growing cycle and that get much bigger at the end of the summer. It can if you have time, it's more efficient to actually split that into two applications and to say put half or two thirds at planting, and then to do what we call side dressing midway through the growing season, so that there's a fresh batch of nutrients as the plants put on a big spurt of growth. For example, when your sweet corn plants are maybe knee high or thigh high that's a good time to add that rest of that fertility. The same goes for when, you know, cucurbit crops are just starting to run, their vines are just starting to run, or when tomatoes or peppers are just starting to bloom. So you can split these, for long growing long season growing crops. But if it's easier, I would suggest putting it down right up front before planting. And then assuming that the plant is going to take that up as it needs it throughout the growing season.

Nate Bernitz  15:28  
And when you say put down and side dressing, you're you're talking about techniques for fertilizer application. Can you talk a little bit more about that? Are we talking about just broadcasting fertilizer into the bed? Are we talking about tilling fertilizer in and if so to what depth and side dressing? What does that mean?

Becky Sideman  15:52  
Right. So if you're putting the fertilizer before you plant the crop, the idea that you want to have in mind is that you want the fertilizer to be where the roots of the crop are going to be, and you want it to be distributed throughout that area. And so yes, if you're rototilling or something like that, you could put the amount of fertilizer you need for a given area and then till it in. Which it would be going four six inches deep around soil rooting depth profile. if you're not telling this might mean you put it on the soil surface, and then you spade it in, or you broadfork it in, or you somehow or other get it down into the soil. You don't just want it laying on the soil surface, you'd like it to get down under and into where the roots are going to be for the crop. That's for if you, when you, apply before planting. When I'm talking about the side dress applications, which means putting more fertilizer while the crop's already there, usually the strategy there would be to put that alongside the crop not touching the crop, but alongside. And then to sort of scratch it in gently just into the soft surface with a hoe or a rake or a trowel, something to just basically slightly incorporate it into the very top soil surface. So that it's not just sitting right on the top, it's mixed in a little bit without without disturbing the roots. And again, this is for an annual crop where you have bare soil. For something like a perennial crop like a blueberry bush or fruit trees, you're really not going to be mixing this in, you're going to be putting this on the soil surface and just making sure that it's, you know, kind of distributed around the root zone.

Nate Bernitz  17:48  
So, let's say that you've tested your soil through UNH, and you have an amount per 100 square feet, maybe you've done some math to get it from 1000 to 100 square feet more of a garden scale. How does that translate to knowing how much to side dress around a particular plant? Or how to put, how much to put in a particular row? And from a technique standpoint, how do you actually ensure that that sort of even distribution so that when you get that total amount in your hands that you know needs to be added to a full area? How do you get that to be somewhat precise?

Becky Sideman  18:29  
Well, I'll say my way, and then we'll see what Emma has to add to that. So what I like to do is I calculate in my vegetable garden, I have rows. And this is true for my fruits as well. So I've got rows and I know how long what long those rows are and how wide those rows are. And you know, for a 50 foot row that's a couple feet wide, there's my 100 square feet. So no matter what the sizes you're working with, I would calculate out how much fertilizer it is per row. And then I take containers, and I weigh out the fertilizers I'm going to use and I have them marked then with volumes and I know that I'm going to use, for the fertilizers, I'm going to use, say two and a half yogurt containers. I'm making this up but you get the idea, per row. And I'm going to then just very gently walk down and back and down and back until I've got this, and you get good at it after one or two rows. And I have that calculated out so it's the math is easy. I'm not always rethinking it. I know that for the vegetable garden, I'm gonna need roughly this amount per row, and I can put it right before planting. And again, fork it in and then plant and so I've really kind of taken the thinking out of it ahead of time by sort of doing that math ahead of time

Emma Erler  20:00  
I think that makes a lot of sense and could be applied to other areas of the landscape too. Particularly lawn areas, if you're fertilizing your lawn, measuring out exactly what the square footage of your lawn is, is is something that you're going to need to do if you're going to fertilize correctly. And the same goes for annual or perennial flowerbed. If you're trying to fertilize a tree, you're probably trying to get that fertilizer within the drip line of the tree where most of those roots are going to be. So that means going out to the farthest extending branch and dropping a make believe line, and figuring out you know what that diameter is around for spreading that fertilizer. It's, I think, absolutely essential to do this before you go to the store to figure out what sort of fertilizer you need, so that you have an idea how much space you have, and then exactly how much product you're actually going to need to buy. You know, if you have soil test results, you might have gotten instructions on exactly what you need to apply how much you need to apply. Without soil test results, then you're probably going to be relying on what the instructions are on that fertilizer package to see how much you should put down based on the recommended rate either going with that rate or a bit lower. I would never go above the recommended rate on the package. But even so, even if you're just going with that fertilizer package, you're going to need to know how much area you have, so that you're buying the appropriate amount of fertilizer, and not overspending, not over applying.

Nate Bernitz  21:48  
We've got to take a quick break here. This isn't an ad per se, but I do want to plug our spring webinar series, we'll have the requisite links in the show notes. But we have upcoming webinars on supporting pollinators in your landscape, getting the most out of compost and manure, and using drip irrigation in the garden. These webinars introduce a visual element to what we're doing here on the podcast, I hope you'll check them out. Alright, thanks for indulging me, let's get back to my conversation with Becky and Emma.

How are you timing those applications? And what's influencing the rate? I think I've seen that you might actually change your rate as a tree grows. So I'm kind of curious about that. And whether there's any corollary to say, landscape trees. And I'm curious about the soil test results, are we getting results that are like per 100 square feet? Or are they more results per tree or per bush.

Becky Sideman  22:53  
So for fruit trees, and for blueberry bushes, things like that, where we're harvesting a crop off, we do, our recommendations are per bush or per area depending on the kind of soil tests that you, the form that you use, but it's usually per bush or per tree for a home gardener. And those amounts increase as the bush or tree gets older. So for a young newly planted bush or tree, there would not be much fertilizer applied. But once they get into full production, then there would be an annual application. And often with a fruit tree, if there was not a crop removed the year before, you might not actually apply fertilizers because you are replacing those nutrients that were removed with the crop as you picked all the apples from the apple tree, for example. But as a general rule, the larger and older the tree is, the more nutrients we would recommend applying for that. And as far as the timing goes, yes, it's really similar it would be early spring. And we might suggest a split application where you would apply half of it early, like about now as they're starting to like produce leaves and starting to grow. And then three to four weeks later, when they've really started growing and taken off.

Nate Bernitz  24:32  
So just to clarify that first application is not a dormant application is when you're starting to see foliage growth.

Becky Sideman  24:39  
Yeah, or bloom time, which is just before you'd start to see foliage growth. So the idea is that you want the nutrients there when the plant is going to start to push new growth. And so that's the idea, you don't want it there long before because you would lose it, possibly with rains. And you don't don't want it there, after they've already put on all their growth for the year. So there's kind of it's a spring window basically,

Nate Bernitz  25:07  
Oh and if you're just putting granular fertilizer around the drip line of, say, an apple tree, what's to prevent that from just washing away in the rain? 

Becky Sideman  25:16  
It could. And that's sort of a, I don't think it usu-. If there's mulch there, or if there's grass there, depending on kind of how you have that set up, you might rake it in so that it is unlikely to wash away. But certainly, if you are on a big slope, that would be a concern that that would definitely be a concern. 

Nate Bernitz  25:40  
In terms of fertilizer selection, there, there's a few different factors or variables from product to product that I've noticed. One of them is the ratio of nutrients. Another is the the release rate of the nitrogen. Or, I've seen that as described as slow release nitrogen or as water soluble or insoluble nitrogen. If you get soil test results, it's going to give specifications on ratio of nutrients. But say you don't have those soil test results. How might you think about the desirable ratio for for New Hampshire soil? And for the for the plants who might be growing? And what sort of release rate are you looking for? And again, does it depend on what you're growing?

Emma Erler  26:32  
Yeah, again, it that definitely depends on on what you're growing. And, yeah, so let's start there. Those three numbers, so every single fertilizer that you purchase is going to have what's called the guaranteed analysis. And that's going to tell you the percentage by weight of a nutrient that's in that product. And the three numbers that you'll see on a fertilizer package represent the nitrogen, phosphorus, and potassium in that product, in that order. So for example, if you had a 10 10 10 fertilizer, that would mean that by weight, there's 10% nitrogen in that product 10%, phosphorus, and 10% potassium. So this definitely matters. Based on your soil test results, it's it's you may need some of these nutrients, you may not. With a lot of New Hampshire soils. And really the majority of the soil test reports that I've seen for home gardeners, the soil is already high or very high in phosphorus. It's it's quite rare that somebody actually needs to add phosphorus to their garden soil. Although it, it does happen occasionally. So it is useful to have those results. If you have absolutely zero idea of what's in your soil, and you have no intention of testing your soil. And then it probably does make sense to put down a complete fertilizer that contains all three of those essential macronutrients. If you find out that, let's say your your phosphorus level is already optimal, or let's say high, then you might want to put down a zero or low phosphorus fertilizer. That's often the case for pretty much every lawn home lawn soil sample I see there's there's very, very rarely any needed. with nitrogen, which we talked about in the last episode, there really isn't a reliable way to test for it. So nitrogen recommendations are just based off of research on you know, the plant response basically to certain rates applied. So we just have these general guidelines there. But with nitrogen, it can come in two forms. Basically you can have your slow release or water insoluble nitrogen, or you can have your water soluble, just quick release forms of nitrogen. That water soluble nitrogen. It won't be listed as that on the product label it will probably say ammoniacal nitrogen or urea nitrogen. Some products might say water soluble nitrogen, that is nitrogen in a form that the plant can take up immediately. So you put that fertilizer on the on the soil, or you might it might even be a liquid form. And as soon as that fertilizer is in solution in water, the plant can take it up can take up those or that nitrogen. If you have a water insoluble nitrogen, that nitrogen is not immediately available to the plant and with a lot of slow release fertilizers. Sometimes the nitrogen is actually encapsulated. So that it is, it will release slowly over time, depending on the temperature of the soil, the moisture in the soil, so that if you have, you know, a warm, or I should say if you have a consistently moist soil, those nutrients are going to be releasing slowly over time, if it's very, very dry, you're not going to get very much release at all. Useful to note too that with water insoluble nitrogen, and in many cases, especially if this is an organic source of nitrogen, that nitrogen might actually have to be converted by soil micro organisms into a form that plants can actually use. So this takes time. And you do need to have a microbial healthy microbial community in your soil in order for this to happen. So that's that that's where having, you know, a healthy amount of organic matter in your soil can be important too, so that you have the healthy population of bacteria and fungi that can make the nitrogen available to your crops. So yeah, that was a lot. But basically, that that water soluble nitrogen plants are going to be able to use right away, water insoluble, it's going to have to be broken down before plants can access it.

Nate Bernitz  31:33  
Emma, can you give maybe an example where you would definitely want a very heavy amount of slow release nitrogen, and then maybe an inverse example where you would want a product that is mostly fast release?

Emma Erler  31:49  
For I mean, I'm thinking when I'm when I'm talking about lawns, or certainly trees or shrubs, there really isn't, there are too many times when you need a whole bunch of nitrogen, let's say available all at once. These are perennial plants that are that are growing over time. So having the nutrients release slowly over time, you know, at a rate the plant can actually take it up as important. I think this is particularly key if you live near a water body. So if you live near a lake, if you live near a stream or a pond, if you're putting down a whole bunch of nutrients that plants can't use, a lot of it's going to leach out. And you could have pollution issues, essentially, particularly with nitrogen, if you're near the ocean, or near near a bay where there's there's a saltwater community. So if you're using this slower release product, you're less likely to have you know, excess nutrients leaching out of the soil profile. So that's kind of the thinking there too. And you're less likely to burn plants. That's something we haven't really talked about yet. But if you are putting down too much of a synthetic fertilizer all at once, you could end up burning the roots of that plant. Because there are salts in these products versus that slow release product where it's it's breaking down over time, you're not likely to end up if you're applying it correctly, not likely to end up with any sort of issue with a toxicity or burning.

Nate Bernitz  33:29  
Becky, do you want to jump in and maybe give examples in like a vegetable or fruit production standpoint where, I don't know, you're going with fertilizers that are kind of heavier nitrogen or have less nitrogen or, or and or, more fast release or slow release forms, like, kind of take us through some strategic thinking on how you would go about selecting products with different traits in specific situations.

Becky Sideman  33:59  
Yeah, I sort of similar to Emma, I think that in most vegetable garden and fruit production settings, a slow release product works well. Because it's going to gradually release nutrients in the early part of the season. Most most slow release products, unless you buy those encapsulated ones that have like an 18 month or longer predicted lifespan, mostly they become available within in the order of eight weeks to 10 weeks, which is about when you'd want them in a garden setting. So I would say, in most cases, slow release products make sense. So one example where I can think that you'd want pretty readily available nutrients is when you're growing transplants to raise young plants to go out into the garden when you want those nutrients, as the little transplants are growing, you want those to be available right then. And so that's probably the one case where I would say you really want rapidly available. If you get, if you rely on totally immediately soluble nutrient sources, you do, it's more important, then, to split your applications into multiple applications so that you hedge your bets against rainfall taking those nutrients away, for example. So I think it's kind of more, it's more insurance to go with a slower release product, or a blended product. And I can't agree more with Emma's assessment of how you choose those materials based on what your soil test says. And if you don't have one, then you probably should pick something that is a complete fertilizer that has all three of the macronutrients plus micros, to cover your bases.

Nate Bernitz  36:03  
So in terms of slow release, first fast release, and like Emma said, fast release might be called ammoniacal, water soluble nitrogen, and then you've got your water insoluble nitrogen, what sort of ratios between those two might you expect? Like, if you're seeing some of both, what's a kind of good percentage of slow release nitrogen, if if you are seeing some of both?

Emma Erler  36:29  
Gosh, I mean, that can vary so much, you know, between fertilizers, I would say, if you're looking at it from an environmental standpoint, I would, I would be looking for a product that contains probably at least 25%, water insoluble, or slow release nitrogen, just so that you aren't going to lose all those nutrients right away with with rainfall. So there's a lot of these out there, you just need to look at the fertilizer label, particularly for if you're talking about a lawn fertilizer, let's say. Just look on the back there, if you don't see anything that says water insoluble, or slow release, then that's probably not what you're looking for, if you're trying to be a good environmental steward. So 25% I'd say is, is really the the minimum higher is fabulous, too. So that's, that's totally fine. And a lot of the organic fertilizers are going to have a higher percentage of water insoluble nitrogen,

Nate Bernitz  37:32  
I just pulled up the guaranteed analysis for a popular garden fertilizer, and so it's 3% nitrogen total. And that's broken down into 0.2% ammoniacal, 0.6% other watersoluble, and 2.2% water insoluble, and then at the bottom, it says 2.2%, slow release nitrogen. But that's kind of confusing, because it's up in what you're talking about with 20 25%. That's of the amount of nitrogen. So if you looked at this product through that lens, you might be like, wow, there's almost no slow release nitrogen, but actually, it's the majority of the nitrogen that's slow release in this product.

Emma Erler  38:16  
Yeah, you have to look at the percentage of the slow release to the total amount of nitrogen that's in that product. So that example you had there where it was 3% nitrogen, and over 2% was slow release nitrogen, then that's great. You're looking at, you know, over 60% of that, of that product is a slow release. So great.

Nate Bernitz  38:44  
Becky, for a closing question. Can you talk briefly about the difference between organic and synthetic fertilizer? And maybe do you have any favorite organic fertilizers? Not like brands necessarily, but sources.

Becky Sideman  38:59  
So synthetic fertilizers tend to when you're purchasing them, they tend to come in higher percentages. So they provide more units of N, P, and K per total unit of fertilizer, but they also tend to be more quickly available, which you could look at it as a good thing. But as Emma was just discussing, if you want them to stick around for a while, that's, that's kind of less favorable. So there's, there's pros and cons in both directions. Organic sources tend to be lower in nutrients overall, but almost exclusively are slow release as long as you have microbes available to mineralize those, and for that reason, I tend to favor them in lots of settings. One of my favorite organic fertilizers is actually not marketed as a fertilizer. It's marketed as feed. So it's soybean meal. Soybean meal, alfalfa meal, peanut meal, other seed meals like this plant meals tend to be pretty high in nitrogen, and provide smaller amounts of phosphorus and potassium, and provide the full suite of micronutrients. And so for a lot of soil testing applications, that's a really good amendments to use, because you can pair them with something that's higher in P or K, if you need that in your garden settings, some kind of mineral like salt bomag, for potassium or something like that. But it's a readily available inexpensive source of nitrogen. Yeah, so I think I, I feel like my, my thinking when I'm trying to choose fertilizers has to do with not only sort of what it's giving me in terms of nitrogen, phosphorus, potassium compared to what I need, or what my soil test thinks I need, but also what's available to me at local places to get it. And that's affordable per unit of nitrogen, so or whatever element I'm interested in. So it's this kind of dance with figuring out what are readily available byproducts from other industries that I could use. And so those are kind of the things I think about when I'm trying to choose between this myriad of options.

Nate Bernitz  41:50  
Okay, so Becky just had to jet but, Emma, I'm thinking we stick around for a few more minutes. I've got some questions just burning a hole in my pocket that I didn't get to. I'm thinking let's actually jump back to when to apply fertilizer, focusing on trees and shrubs timings a bit different for our ornamental trees and shrubs. Right? Why is that

Emma Erler  42:09  
Um, Honestly, it doesn't have to be that different, I would say that probably the best time to fertilize trees and shrubs, is going to be early spring, before growth is starting. So maybe just as those buds are starting to expand, so that those those nutrients are available while that plant is actively growing. Ideally, that is going to be a slow release form of nitrogen, so that it's not just immediately available to the plant, you know, this is hopefully available over the course of the season. Usually, we don't recommend fertilizing these plants, though, while they're actively growing shoots. So, right before is helpful, but putting down a whole bunch while those shoots are expanding, you may not see that great of uptake with the, with trees and shrubs anyways, so doing it early or waiting until after that growth is slowed down can be helpful. big reason for that is that we're looking for more root growth than anything on mature plants. So, we want to put down that fertilizer source, particular, when the plant is doing more root growth as opposed to shoot growth, perhaps. But if you're using a slow release are an organic source of nutrient, it becomes a little less important exactly when you put it down. Something you probably do want to avoid those putting down a really high nitrogen source of fertilizer that's that's going to release quickly or immediately late in the season, because with some plants that might delay their hardening off for winter, it might might cause them to put on a whole bunch of excess growth later in the season. So that that's something that I would definitely be inclined to avoid. Something I'll also say too, is that with trees and shrubs, and perennials, too, we don't usually need to really add that much fertilizer, and I'd say this is particularly true for landscape trees, landscape shrubs. A lot of times people don't want these plants to put on an excessive amount of growth, because you want them to still fit a certain place in your landscape for as long as possible. You don't want a tree or a shrub to get too big if it's right up against the foundation of your home. So if you're a little bit more sparing with the nutrients, its growth isn't going to be excessive and you won't have to be worrying about pruning that plant too much to keep it to size. Another thing too worth considering, at least when we're talking about, you know, flowering shrubs, or with some perennials, with annual flowers too, you are actually more likely to get more flowers if you're a little bit lighter with the fertilizer, particularly with nitrogen. If you're putting down way too much nitrogen fertilization, the plant will put a lot more energy into vegetative growth, as opposed to flower bud development. So you'll you'll have a much more beautiful plant, if you're very, very light with the nutrients. And these plants too aren't going to use a whole lot. So if you are putting down, let's say, a top dressing of compost, or an organic mulch, a lot of the nutrients that those plants are going to need is going to come from that particular source. The only time I'm really thinking about fertilizing trees, or shrubs, specifically is if their growth seems very small, or if I'm seeing some clear evidence of a nutrient deficiency, and the pH is within a reasonable range. Otherwise, they're probably getting what they need. And if you're fertilizing a lawn area nearby, where these things are planted, then they're definitely getting what they need and don't need anything extra.

Nate Bernitz  46:18  
Something that confuses me is that a lot of fertilizer products are labeled as being food for plants. And that kind of contradicts some of what you and Becky have talked about as far as how fertilizer actually works. So is there, are there some types of fertilizers that really are kind of plant food, or is that a little bit of a misnomer

Emma Erler  46:44  
anthropomorphizing plants, so thinking of them more as people or animals where we need to eat things, in order to get our energy. That's not true with plants, plants are actually making their own energy through photosynthesis. And they're getting a lot of what they need just from sunlight, from carbon dioxide, and from water. So the nutrients that we're putting in with the fertilizer, it's it's probably more, I guess, akin to vitamins, where none of us can live, you know, a human being can't live off of just vitamins, but we do need them in our diet. That's kind of the way I think of fertilizers for plants, where they do need these nutrients, but they don't need them in in vast, vast quantities. So if a plant is getting plenty of sunlight, plenty of carbon dioxide, which is hard for it not to since there's so much in our atmosphere, and plenty of water, then those are the basic things it needs for growth. And then it just needs some of these nutrients that it's taking up through its root system, in order to complete its life processes and be as healthy as possible.

Nate Bernitz  47:59  
I guess another topic that comes up for me that I mean, that one was come kind of from shopping at garden centers. And this is another one from shopping at garden centers is you'll see lots of fertilizer products that are labeled for very specific use. So this is a rose fertilizer, this is a tomato fertilizer, this is a starter fertilizer. How important are these different uses? Because you and Becky, again, haven't really talked through that lens, you've really just talked more through the guaranteed analysis. But are you getting something extra or extra targeted from some of these fertilizers that are labeled for specific uses?

Emma Erler  48:40  
typically, you are getting something that's a little bit more targeted. So some plants might be a heavier nitrogen feeder, let's say or, or we might know that they they need more phosphorus or potassium to be at their best. So getting these specialized formulations can be really helpful. It can also be a little bit on the expensive side. Because a lot of times these specialty fertilizers come in small packages, which, you know, might be impractical if you have a very large garden. More often than not, you can get away with more of a general use product for what you're growing then something that is very, very specific. That being said, a lot of these specific products work great. So totally fine. For let's say something in the landscape. A lot of people use specific fertilizers that are meant for evergreens that have more of an acidifying effect on the soil. So yeah, these are a great option. Are they the end all be all though, like no there there are plenty of other more general products that would do the same purpose you know, as long as you're paying attention to and managing pH, which you should always be doing anyways. So yeah, you can totally get just the the tomato fertilizer in the store, and that that might work great. But you could also probably get great results just from using the general fertilizer that you're going to have throughout your entire garden.

Nate Bernitz  50:14  
And you're saying more bang for the buck for going with those general fertilizers, or at least potentially.

Emma Erler  50:21  
potentially, yeah, just going based on your soil test results, if you have them. picking out a product that's that's going to check all the boxes in terms of what you really need, based on the crops you're growing is, is more important than buying a different fertilizer for every single crop you're growing.

Nate Bernitz  50:41  
Right, I mean, gardening is pretty expensive when you add everything up. So I am always looking for where maybe I don't have to go with the most expensive option. But some things you definitely get what you pay for. So sometimes it's hard to know.

Emma Erler  50:56  
It is yeah, and some people might like to experiment a little bit too. If you're buying fertilizer appropriately, you're not buying more than you're going to use in a single season. So if you're not happy with the results you had one season, there's certainly no harm in making note of that and trying something different the next year.

Nate Bernitz  51:18  
Are you saying that you can't buy a big bag of fertilizer and keep using it year after year.

Emma Erler  51:24  
It kind of depends. Some of these fertilizers if they're stored properly, so stored totally dry in a in a sealed container can last multiple years. But if if any humidity gets at that product, any moisture certainly a lot of times these products can end up degrading. And that guaranteed analysis that's on that that label might no longer be accurate. And frankly, a lot of us too might not really want to have the space taken up storing a massive 50 pound bag of fertilizer that we're only using five pounds of each year. So I definitely advocate for just buying what you need. And then starting over and the next year and getting again exactly what you need and the quantity that you roughly need.

Time for a featured question from a listener. Should I use fertilizer spikes for granular fertilizer for my trees and shrubs? In my experience, broadcast granular fertilizers work best on trees and shrubs because they feed the entire root area. The disadvantage of fertilizer spikes is that they only provide nutrients to the roots that are immediately next to the spikes. However, a better question might be whether trees and shrubs need fertilizer at all. In nature, woody plants receive the nutrients they need from decomposing leaves and needles. Though, fallen leaves are often removed in landscapes. They're usually replaced with organic mulches, which add some nutrients to the soil as they break down. Another thing to consider is whether you're already applying fertilizer near trees and shrubs for other plants, such as over a lawn area. If so, it's likely that trees are already getting everything they need. fertilizer may be beneficial in some situations, though, where trees and shrubs have a restricted root zone that cannot expand enough for the roots to absorb sufficient nutrients to support healthy growth. For example, tree pits and sidewalks, parking lot islands narrow planting strips between the road and the sidewalk. Landscape containers or berms. When in doubt, it never hurts to have your soil tested.

Nate Bernitz  53:54  
And one example of where there seem to be fertilizer products for every situation is lawn care. There's a fertilizer for starting a lawn there's a fertilizer for the end of the season. What do you make of those different products? Do you think it's worthwhile to kind of go off of that fertilizer schedule and use the right product at the right time of year? Or do you kind of go with the same product year round? What was your general approach there?

Emma Erler  54:24  
I typically go with one product and use it year round. And that sometimes might mean a product that says winter feed on it. But you know based on soil test results if that has the right ratio of nutrients, then it's perfectly acceptable to be using that at any point during the season. Those a lot of these let's say for step three step whatever program that we have, can work okay, you know, if you just if you don't have any soil test results at all and you don't know what's going on with your soil. The big problem, I would say, comes down to more putting down things you don't need, namely, that phosphorus that I keep talking about. A lot of times these these products are chock full of phosphorus, and you don't need it in New Hampshire and you could be contributing to particularly with the phosphorus, algae blooms and pollution of a local lake, stream, pond, whatever, if you're putting down excess phosphorus that you don't need. typically the only time you, for a lawn anyways, the only time you really might need to put down a phosphorus fertilizer is when you're just getting started. So a starter fertilizer for lawn might have higher phosphorus because that's good for root development. But, as always, getting your soil tested to see if even that is necessary is really the best way to be a good steward of the land, good steward of your soil. I will note that having something like excess phosphorus in your soil isn't isn't necessarily going to hurt plants. The bigger concern is just the environmental impacts. So, I like to just pick a product that that checks the boxes off and I ignore whether it's telling me to apply it at a certain season. And just go with that for all my applications.

Nate Bernitz  56:25  
On again on cost, I mean, you said, hey, a three, four or five step program can work okay, but those are really expensive, I'd want better than okay, if I'm dropping the money on those as opposed to just using some basic, I don't know 10, zero 10 or something

Emma Erler  56:40  
totally yeah, and if you have a small lawn area, if you're buying four different bags of fertilizer, you may not be able to use all of those in a season. But if you just buy one that meets, really meets the needs of your soil in the grass plants, that that might be all you need. Just that one bag,

Nate Bernitz  56:58  
kind of moving over to the flower garden for a second, something we often get questions about is what to put in the planting hole when you're planting bulbs. How do you kind of come down on that? Are you a bone meal advocate or what? What's your approach there?

Emma Erler  57:15  
Usually with bulbs, I don't really advocate actually putting any fertilizer in the planting hole. When you buy a new bulb, typically that thing is is really robust, it already has really nice flower buds formed on the inside of it. And it doesn't need a whole lot of nutrients right off the bat. So putting nutrients into the soil with that bulb in the fall may not really end up doing all that much. Instead, probably a better idea is actually to fertilize your bulbs after they've flowered in the springtime. That's when that bulb is is needing to recharge so that you get a good bloom the following season. So that's what that's what I'd be doing it. There is. You know, cer- there's certainly a lot of people that swear by putting something like bone meal into the planting hole with their bulbs when they're when they're actually putting them in the ground the first time and that's, that's for a source of phosphorus, which again, most garden soils in New Hampshire already have more than enough phosphorus. But there's there's some evidence that that might attract rodents or, or other pests, maybe a neighborhood dog or something that will then dig up your bulbs. So I try to avoid putting anything down that might attract any sort of nuisance wildlife, particularly if I'm growing something like tulips, which are really favored by a lot of wildlife species.

Nate Bernitz  58:45  
I also hear people using bone meal for root crops. Do you do you think it has some merit there in New Hampshire?

Emma Erler  58:53  
Again, I'm guessing probably not. It's it's very rare, very rare that anybody really needs to add phosphorus to their soil. And phosphorus is is very, very good for root growth. But only you're only going to notice a difference if that phosphorus is actually limiting growth in your soil. Which I think is is probably unlikely.

Nate Bernitz  59:21  
Yeah, and I guess what comes to mind for me is so you're saying not only are New Hampshire soils, naturally high in phosphorus, but any compost and manure we're adding and likely gardeners listening or adding that kind of organic material maybe every year. That has phosphorus too

Emma Erler  59:39  
it does, yeah, so adding a specific phosphorus fertilizers, most likely unnecessary.

Nate Bernitz  59:47  
So we've talked really exclusively about adding fertilizer to the soil. But another way of adding fertilizer that I know many commercial growers use is foliar applications spraying fertilizer directly onto the leaves, what merit does that have, in your view for gardeners Is that something the advanced gardener should be seriously considering?

Emma Erler  1:00:13  
You know, it's it's probably not something that I would ever advocate for, for the home gardener. That's something that has to be very, very precise. Sometimes it can be really effective, sometimes not. And even in in, you know, commercial settings, there's kind of mixed reviews on how effective that is, and whether it's really worthwhile and maybe more appropriate for certain nutrients over others. So for the majority of your fertilizer application, it's really gonna be important to put those nutrients where a plant would normally take them up anyways, which is in the soil where those, those would naturally be found. So I think it's going to be more efficient to go that route. And also you're really more likely going to be able to buy nutrients, you know, in that form or for that purpose. I certainly wouldn't bother going out and and hosing plants down with with a spray bottle of say Epsom salts or something, I don't think that you're really going to notice any good results from that and yeah, not worth the effort just go ahead and use that fertilizer in the soil.

This episode's featured plant is beebalm, also known as bergamont Oswego tea or by its genus monarda. There are a number of species of beebalm that grow wild in the United States, one of them known as wild beebalm monarda fistulosa, can be found growing wild in New Hampshire, and is often a component of wildflower seed mixes for the Northeast. Wild beebalm is an herbaceous perennial plant that grows two to four feet tall and spreads rather quickly by its rhizomes to form large patches. It is a member of the mint family Lamiaceae, which means that it has square stems and opposite leaves that are very fragrant and often used in tea. wild beebalm flowers are both unique and beautiful. blooms consist of two lipped lavender tubular flowers that appear in dense globular terminal heads, atop stems. Each flower head sits atop a whorle of showy pinkish leafy brax. This is truly a unique flower. The best part about bee balm? The flowers are very attractive to bees, butterflies, and hummingbirds. Making this plant a must for any native plant garden, pollinator garden, naturalized area, or rain garden. If you're interested in growing bee balm, you'll have good luck if you plant it in a dry to medium moisture, well drained soil, in full sun to part shade. It's an easy plant to grow, and I'm sure you'll have good luck with it in your own garden. And finally, a closing tip. Did you know that New Hampshire has a turf fertilizer law? In order to combat the pollution of New Hampshire's waterways from excess nitrogen and phosphorus from fertilizer, the New Hampshire legislature passed a bill in 2013 regulating the use of nitrogen and phosphorus turf fertilizers that are sold at retail. The goal? To help homeowners maintain healthy lawns without applying unnecessary fertilizer. So what's in this law? Essentially, no fertilizer sold at retail shall exceed 0.9 pounds per 1000 square feet of total nitrogen per application, when applied according to the instructions on the label. Furthermore, no turf fertilizers sold at retail shall exceed 0.7 pounds per 1000 square feet of total soluble nitrogen per application, when applied according to the label. Additionally, the instructions on the label should indicate that you apply no more than 3.25 pounds per 1000 square feet of total nitrogen. There's also a limit on how much phosphorus can be in retail turf fertilizers. So what does this mean for the home lawn? Well, as long as you apply turf fertilizer at no more than the recommended rate that's on the product label. You'll be giving your lawn the nutrients it needs without putting down excess fertilizer that could pollute lakes, ponds, rivers, and streams. And that's a good thing for all of us.

Nate Bernitz  1:04:51  
that's gonna do it for this two part series on soil amendments and fertilizers. I hope you enjoyed both episodes and took away some new ideas to put to use, Emma and I are trying something different for our next episode, recording at a garden center instead of from a studio. We'll chat with customers and explore the selections sharing our tips for how to get the most out of your next trip to your local garden center or nursery, just in time for New Hampshire's biggest gardening weekend of the year. You can reach Emma and I by email at We're loving your questions, feedback and suggestions. Until next time, keep on fertilizing your yard and garden Granite State Gardeners, talk to you again next Friday. Granite State Gardening is a production of the University of New Hampshire Cooperative Extension an equal opportunity educator and employer. Views expressed on this podcast are not necessarily those of the university's its trustees, or its volunteers. inclusion or exclusion of commercial products in this podcast does not imply endorsement. The University of New Hampshire US Department of Agriculture and New Hampshire Counties cooperate to provide extension programming in the Granite State. Learn more at

Transcribed by


Nate Bernitz
Public Engagement Program Manager
Extension Program Mgr
Phone: 603-351-3831
Office: Cooperative Extension, Taylor Hall, Durham, NH 03824

Emma Erler
Landscape and Greenhouse Field Specialist
Instructor Field Specialist
Phone: 603-641-6060
Office: Cooperative Extension, Taylor Hall, Durham, NH 03824

Rebecca Sideman
Sustainable Horticulture State Specialist
Full Extension State Spec/Prof
Phone: (603) 862-3203
Office: Cooperative Extension, Kendall Hall, Durham, NH 03824