Buying Topsoil

Topsoil. Some biologists call it the most precious stuff on earth. It takes nature 500 years to make an inch of it.

In the past 30 years topsoil has become a hot commodity in New Hampshire, removed by land developers and sold to meet the swelling demand from homeowners and businesses looking to establish or improve lawns and gardens.

Land scarcity in many areas, combined with new building techniques, allows construction on steep, rocky sites once considered unbuildable. This makes importing topsoil the only option for home or business owners who want a lawn or garden on those sites.

The soil you buy might have come from recently-cultivated farmland, from a recently clear-cut tract of forest land, or from a long-abandoned field. It might contain herbicide residues that could inhibit germination of some of the plants you want to grow. It might be full of roots and rocks or undesirable weed seeds.

A vendor might even have adulterated the original topsoil with a lot of additional sand, adding commercial wood ashes to darken the final product. On the other hand, some topsoil vendors manufacture a superior growing medium, amending native topsoil with just enough wood ashes to bring its pH into the optimum range for lawns and gardens, then adding compost to boost the soil's water- and nutrient-holding capacity.
Like most states, New Hampshire has no regulations defining quality standards for topsoil or governing its sale. To protect yourself, experts suggest learning as much as possible about the soil you plan to buy before you buy it. Consider it worth your time. After all, you can't take this product back to the store!

This list of guidelines from experts will help boost your confidence that the topsoil you buy will grow good vegetables, fruits, flowers, or a nice lawn:

• Know your supplier and ask about the source of the topsoil he or she sells. If a vendor has advertised an "amended" product, ask for the 'recipe'-in writing.
  
  
• If you plan to buy your soil from a garden or landscape supply center, ask the vendor for the product's test data. If the vendor hasn't had the product tested, ask for a small sample and have it tested yourself. Call the UNH Cooperative Extension Info Line (1-877-398-4769, Monday-Friday, 9:00 a.m.-2:00 p.m.) for information about soil testing.
  
  At the very least, soil experts say, the soil analysis should include pH (a measure of the relative acidity of the soil) and soil texture class (a classification based on the relative percentages of sand, silt and clay particles in the soil).
  
  While you can raise or lower a soil's pH and add nutrients, you can't realistically change a soil's texture. Look for a texture classification of loam or sandy loam. Soils with a high percentage of sand won't hold water or nutrients well, while high-clay soils won't drain well and can become extremely difficult to work.
  
  
• If you haven't seen the topsoil, ask if the vendor has screened the loam to remove rocks and roots. For the right price, you might find yourself willing to rake them out yourself if the price is right, but it's definitely something you'll want to know about up front.
  
  
• Don't buy a product that has a chemical smell or other off-odor. Vendors might have adulterated the topsoil with petroleum-contaminated soils or other potentially toxic waste products.
  
  
• Occasionally, topsoil stripped from former farmland may contain herbicide residues that could hinder crop germination. If you have concerns about residues, take a soil sample home, plant a few seeds in it and see if they germinate well. Herbicide residues can affect some crops but not others, so plant a variety of different seeds, especially if you plan to plant a vegetable garden in this soil. The process of test-germinating seeds will also help a prospective buyer determine if the soil is infested with difficult-to-control perennial weeds, such as quackgrass or thistles.

Whatever its source, the topsoil you buy may lack organic matter, important for holding moisture, improving soil structure and retaining plant nutrients. Add plenty of organic matter in the form of compost and animal manure. Make sure to compost manure before adding it to soil that will grow food crops, or plant a cover crop and turn it under before planting vegetables.

Finally, make sure to incorporate both the organic matter and the purchased topsoil into the existing soil, rather than simply spreading the new soil on top. Plant roots grow best in a single zone of topsoil.

By Peg Boyles, University of New Hampshire Cooperative Extension Master Gardener

For more information call the UNH Cooperative Extension's Family, Home & Garden Center's Info-line (toll free) at 1-877-398-4769 or send us an email. Volunteers are available to answer your questions Monday through Friday 9:00am to 2:00 p.m.

4/06/06