GHS Guide to Soil and Soil Testing, Part 1
Did you know that fall is the best time to test your soil? Test results are affected by the bacterial action in the soil, and during summer and fall, the levels of bacterial action are optimal for getting an accurate reading.
However, experienced gardeners prefer to test in the fall because they can fertilize their soil based on the test results, and then, whatever they add to the soil will have time to “set” over the winter. By testing in the fall and then fertilizing based on the results, your garden will be in the best possible shape when the spring growing season rolls around.
There are two tests that are important to do annually: a pH test to determine whether your soil is alkaline or acid and to what degree, and a nutritive test to evaluate how rich your soil is in nitrogen, phosphorus, and potassium (N, P, and K). We’ll talk first about the pH test, because it’s the most important.
Plants grow best within a specific pH range. Most plants like slightly acidic soil; others need a greater degree of acidity, and some prefer alkaline soil. What this means in a practical sense is that when you give your plants the right pH, they will best be able to absorb nutrients in the soil. The right pH will also make your plants less susceptible to plant diseases and fungi.
Many of our soil test kits come with a chart that tells you exactly what pH different plants need, or you can consult a chart on the Internet or find one in a gardening book.
Once you have your pH results, you can then amend your soil accordingly. Adding lime is the usual way to make your soil less acidic. Wood ashes mixed into soil will also help to lessen its acidity. Just be sure to use ashes from untreated wood, and keep them dry until you apply them.
Add sulfur, aluminum sulfate, or gypsum to make soil more acidic. Organic soil amendments such as sphagnum peat moss, oak leaves, coffee grounds, and well-composted sawdust also help to make soil more acidic.
Some fertilizers have an acidifying effect, enabling you to take care of your plants’ nutritive needs while lowering the pH a little. Look for a fertilizer designed for acid-loving plants such as Espoma’s legendary Holly Tone.
Keep in mind, though, that it can take several years to change the fundamental pH of your soil. You don’t want to go too fast: no more than 1 pH degree per year. And you’ll want to test each year, until you see that your soil has really settled into being the pH that you want it to be.
You’ll also want to do an annual nutritive test to determine how much nitrogen, phosphorus, and potassium (N, P, and K) are present in your soil.
If you live near a Cooperative Extension, give them a call: they can do soil testing that will test for other nutrients also, for no more than ten dollars, and carry out the analysis using equipment that is too costly even for most farmers. They also have the expertise to interpret the test results, and can advise you as to how to best address whatever issues show up in them.
That said, do-it-yourself soil testing is more economical than ever. In fact, you can get a Rapitest Model 1609CS containing 4 pH and 2 NPK tests for only $5.25. Though not as accurate as the professional tests, the do-it-yourself tests are more convenient and certainly work well enough to get a valid estimate.
Another advantage of the do-it-yourself tests is that they make it easy to retest after you’ve added fertilizer or other amendments. The Rapitest Electronic Soil Tester, Model 1860 does both NPK and pH in less than a minute, and you can stick it in different spots around your garden to customize your amendment strategy. A week or two after amending your soil, take a stroll around to the same spots to see if the NPK and pH levels are where you want them.
One of our previous newsletters, Choosing a Fertilizer, will help you determine which fertilizer is best for your needs. But don’t wait ’til spring…. seize the season!
In Part Two of the GHS Guide to Soil and Soil Testing, coming up in two weeks, we’ll tell you about two simple tests you can do yourself at no cost that will yield valuable information about the composition of your soil. And we’ll talk about what to do if your soil is lacking in organic matter, doesn’t drain well, contains too much clay, is highly compacted, or has other problems related to its composition.
Until then, happy growing from Garden Harvest Supply!