Cornell Cooperative Extension

April 16, 2012

Gardeners should take time to test soil

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.

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