by Diana Alfuth, horticulture educator for Pierce and St. Croix counties UW-Extension
Sure, your yard and garden soil is frozen and covered with snow — out of sight, out of mind. But now is the BEST time to plan your garden, and that includes planning for great soil!
How long has it been since you’ve had a professional soil test done? Never? You should do a soil test every four to five years, and it’s a small investment for a great, productive garden. While you can purchase soil-testing kits at garden centers, some of them have questionable reliability. It’s better to send a soil sample into a reputable lab to be sure you are getting accurate results. Your local UW-Extension office can help with information on how to collect and submit a soil sample.
Without an accurate soil test, it’s impossible to know what your soil needs! Soil test results will tell you how much phosphorus and potassium — two of the main plant nutrients — are in your soil. If you have adequate amounts, there is no reason to spend money on these fertilizers.
Perhaps the most important thing your soil test tells you is the pH. The pH matters because if it is too high or too low for the plants you are trying to grow, they are not able to take up the nutrients they need. You can have nutrient deficiencies or toxicity if your pH is out of whack. Most garden plants are happy with a pH somewhere between 6.2 and 7.5, but some, such as blueberries, prefer a pH below 5.0. Plants, such as pin oak or white pine, will have yellow foliage caused by an iron deficiency if the pH is too alkaline, even if there’s plenty of iron in the soil.
A soil test from the UW soil lab will tell you not only your pH, phosphorous, and potassium levels, but exactly how much of what to add to get your soil where it needs to be to grow the plants you want to grow. Plan now to do a soil test as soon as the ground thaws in spring.