Groundcovers for New Hampshire

Introduction Groundcovers are fairly low-growing plants that cover the soil with an abundance of stems and leaves. Turf grass is easily the most widely planted groundcover in the landscape, though it isn’t typically categorized that way. In gardening, the term “groundcover” typically applies to vigorous perennial plants that are used in planting beds. Too often, gardeners and landscapers rely on mulch to cover the soil and prevent weed growth. Yet, there is no need for mulch to be the main feature of a planting bed when there are plenty of tough groundcover plants that can do the job just as well or better.
 
Benefits of Groundcovers Groundcovers are not only attractive, but are useful in a variety of situations and provide a number of benefits, such as:
  • Suppress weed growth
  •  Decrease nutrient leaching during heavy rainfall
  •  Reduce soil erosion, especially on slopes
  •  Require less maintenance once established
  •  Provide cover and forage for pollinators and other wildlife
 
Plant Selection Before choosing a groundcover, you need to establish its purpose and the site conditions where it will be planted. Groundcovers are often used as a lawn alternative in areas that are difficult to mow, or are too shady for grass to grow. They can also be a lower maintenance planting option compared with a standard annual and perennial flowerbed. Next, consider whether the area is mainly sunny or shady, the soil is wet or dry, and which planting zone it is in. Aim to match plant growing requirements with the conditions of the site. Lastly, choose plants based on how much maintenance you are willing to do, growth habits, and aesthetics.
 
Some groundcovers are extremely aggressive and may creep into lawns, gardens and natural areas unless carefully managed. Some historically common groundcovers have been added to the New Hampshire Prohibited Invasive Plant Species List or the New Hampshire Plant Species Watch List and should not be planted. These include: creeping Jenny (Lysimachia nummularia), common periwinkle (Vinca minor), bishop’s weed (Aegopodium podagraria) and winter creeper euonymus (Euonymus fortunei). Though not prohibited in the state, a few other plants have similar invasive tendencies and should only be planted in places where their spread is limited by sidewalks or buildings,such as English ivy (Hedera helix), lily of the valley (Convallaria majalis), spotted deadnettle (Lamium maculatum) and chameleon plant (Houttuynia cordata).
 
Planting Before planting a groundcover it is critically important to control all perennial weeds in the planting bed. Perennial weeds that come back year after year, such as quack grass or Canada thistle, are very difficult to eliminate when they become established amid a groundcover. Weeds can be smothered effectively over the course of a growing season by covering them with heavy black plastic or thick layers of newspaper covered with mulch or compost. Using this method, planting can occur in the fall or following spring. Applying a broad-spectrum herbicide directly to perennial weeds is a much faster option, as planting can occur within a week or two of treatment.
 
A soil test is useful for determining nutrient levels as well as pH. Many groundcovers are quite adaptable when it comes to soil conditions, but they will still grow best if the pH is between 6.0 and 7.0. If necessary, adjust the soil pH before planting, or choose plants that can tolerate the current conditions.
 
The best time to plant groundcovers is in the spring or fall when temperatures are mild and precipitation is more frequent. Summer planting is possible, but frequent watering is a necessity during hot, dry weather. Plants should be set in the ground at the same level they were in the pot, or slightly higher to account for added mulch. Mulching bare soil between plants is helpful for keeping weeds under control, at least for a season or two until the groundcover becomes established and covers the soil. Mulch will also decrease erosion on slopes until the plant roots are extensive enough to do the job. Two to three inches of coarse organic mulch should be enough to prevent weed seeds from germinating and limit erosion.
 
Check the soil moisture of newly planted groundcovers at least once a week during the first growing season. When the soil begins to dry out, apply enough irrigation to wet the soil to the root zone of the plants (three to six inches). Overhead sprinklers or drip hoses will work equally well for this purpose, though drip irrigation is more water efficient. Proper spacing between plants depends on the plant species’ growth rate, growth habit, how quickly you want to cover the area, and cost. Faster results naturally come from spacing groundcover plants closely, but depending on the size of the area, this may be too costly. Wider spacing is acceptable as long as weeds are managed regularly until the groundcover fills in. While they are fast growers, it will still take some time for them to entirely cover the soil. Most groundcovers are spaced between six inches and two feet apart.
 
Maintenance Once established, most groundcovers require relatively little maintenance. During periods of drought, some supplemental watering may be necessary to reduce stress on plants. Some groundcovers are more drought tolerant than others, though all will benefit from extra water. Water should be applied until it reaches the root zone of the plants. 
 
In general, groundcovers have fairly low nutrient requirements, and fertilizer may not be necessary for healthy, vigorous growth. If fertilizer is necessary, based on a soil test, choose a slow-release formulation that contains at least 30 to 50 percent slow-release or “water insoluble nitrogen”. These fertilizers will provide a consistent supply of nitrogen to plants throughout the growing season. Compost and manure are other good sources of nutrients that can be applied as a topdressing to build soil organic matter. Fertilizing will have the greatest impact if performed in the early spring shortly before growth starts.
 
Some groundcovers may require some pruning or deadheading to maintain a tidy appearance, such as catmint (Nepeta racemosa) or black-eyed Susan (Rudbeckia species). In most cases, plantings can be maintained fairly easily with hand pruners or hedge shears. Groundcovers planted near trees or shrubs may require some raking or leaf blowing in the fall to remove excess debris. Too many fallen leaves can smother groundcovers or promote disease issues by trapping too much moisture around the foliage.