Getting started: testing your soil

So you want to grow vegetables, and you want to grow them in your back yard soil. Maybe you live in an urban area, and you don't know if your soil might be contaminated with heavy metals. Maybe you just bought your house, and don't know much about the area or your soil. Maybe all three.

Any of these are good reasons to get your soil tested. If you're planning to grow any edibles, especially leafy greens or other annual plants, you'll want to know what you're starting with.

You'll want to test for soil pH, or potential Hydrogen--pH has a huge impact on your plant performance. You can do things to change your soil pH if it is not in a good range for vegetables (you want 6.0 to 7.0). You'll also want to know the extactable nutrients nitrogen (N), potassium (K), Phosphorus (P) at the minimum--these are the most important nutrients for vegetable growth, but not the only ones they need. Commercial fertilizers that have numbers, such as 7-5-4, relate to N, P, and K. Calicium (Ca) and Magnesium (Mg) are important as well, and there are a host of micronutrients which benefit the plants in ways we don't totally understand as yet.

The best test for the money is from U. Mass Amherst--their $9 test will cover soil pH, buffer pH, extractable nutrients (that is, those that are available to plants, based on the pH) Nitrogen (N) Phosphorus(P) , Potassium (K) , Calcium (Ca), Magnesium (Mg) , Iron (Fe) , Manganese (Mn), Copper (Cu) , and Boron (B); the extractable heavy metals (that is, those the plants will take up) Lead, (Pb), Cadmium (Cd), Nickel (Ni), Cromium (Cr), extractable Aluminum (Al); Cation Exchange Capacity, and % Base saturation.

Cation Exchange Capacity measures the potential for your soil to have extractable nutrients your plants need--usually CEC is held in the clay particles of soil. Remember I said clay soil is not so bad? You have to have more than clay to make the nutrients available to plants, but the CEC can show your soil's potential. This can be encouraging for those of us with clay predominant soil.

Base saturation has to do with soil permeability and percolation. You'll want to know how well drained your soil can be, or if it does not drain well.

To take the soil sample, figure out the area of the testing site--maybe you have a space in mind that is 10 feet x 10 feet. From this area, dig down 6 inches (the average root depth) and obtain soil at this depth from several spots evenly spaced within your target site. You'll want to dig 6 to 10 holes in the area, mix the soil you obtain, and from this soil, send 1 cup to U Mass Amherst (or some other extension of your choice). For more specific directions, visit http://umass.edu/soiltest. You can choose to have your results emailed to you (fastest) or snail mailed.

If you have a very large yard, you might consider taking samples from different sections, and sending more than one sample for testing. You'll need to dry your soil sample before sending it. Send it UPS or Fed Ex.

Your results should come back in a week or two. More about reading your results next time.