April 16, 2012

Gardeners should take time to test soil

AMY IVY, Cornell Cooperative Extension

---- — Regular readers have seen me say that the key to success in growing any kind of plant is in the soil.

Healthy soil makes for healthy plants, plain and simple. Adding organic matter is always a good idea, but today I want to focus on another aspect of soil quality, its nutrient content.

I'm not talking so much about pH here, although that is one factor. I'm focusing on actual nutrients and minerals such as potassium, calcium, iron and the current hot topic for anyone in our region: phosphorus.

The only way to know how much of any of these elements is in your soil is to have it tested. That also goes for determining the pH, soluble salt levels and percent organic matter.

For an accurate reading, you really need to send your soil to a lab. Those home soil-testing kits are just not reliable enough, and the probes sold for testing soil pH are also inaccurate. We can test your soil pH in our office using a Cornell test, but for a full nutrient analysis, you need to use a lab.

Why Test?

For most home gardens, a complete nutrient test needs to be done only every few years. It's interesting to see where your soil levels are and to find out which nutrients are lacking and which you have in excess, if any. I especially like this complete test because it tells you the percent organic-matter content of your soil. Don't be surprised if this number is lower than you expected. Home garden soil is usually only 4 to 6 percent organic matter, even after years of improvements. This number varies widely, though, so you'll need a test to find out where you are.

Taking samples

Your test results will be only as accurate as the sample you send in, so take the time to do this properly. Take a small bucket, and use a trowel or shovel to dig 4 to 6 inches into your soil, and take about a half-cup from several spots around your garden area at this depth. Do not include surface soil in your sample. Mix all these scoops together in your bucket, and then take 1 to 2 cups of this mixture for the sample you'll submit. Let your sample air dry before mailing it to the lab.

If you have several garden plots with different conditions or treatments, test each one separately. Be sure that each sample submitted is made up of several smaller samples taken from the garden plot.


You can call or email our office for a copy of the proper form to include with your sample, and we have the sample boxes the lab likes you to use. You can also download the form from For home gardens, use Form H, which tests for 10 different nutrients and costs $12 for the basic test or $17 if you want soluble salts tested, as well.

If you want the abbreviated test for your lawn, use Form T for turf. This will test only the pH and phosphorus level and costs $7.

Nitrogen is not included in any of these tests, even in the standard tests used by commercial growers, because its level fluctuates widely, making an accurate reading nearly impossible.

Once you get your test results back, contact your local extension office for help in interpreting what the results say. If you would include the office on the form when you send in your sample, your results will be emailed there as well as to your home. This makes it easier for us to help you with your results.

Amy Ivy is executive director of Cornell Cooperative Extension, Clinton County. Office phone numbers: Clinton County, 561-7450, Essex County, 962-4810, Franklin County, 483-7403. Website: Email questions to