What's the secret to raising healthy, carefree vegetables and flowers? Great soil. How can you tell if your soil has what plants need? A soil test. When you send a soil sample to a lab, you get a detailed analysis of soil nutrients and you find out about deficiencies. That's valuable information. Now you can also assess your soil for even more critical qualities, using a system developed by a team of farmers and soil scientists in Oregon. The methods are quite simple and the only supplies you need are a few items commonly found around the house.
The system, called Willamette Valley Soil Quality Guide, was designed with farmers in mind. But it can be used by gardeners in most zones across the country, says Richard Dick, Ph.D., codeveloper of the system and a professor of soil science at Oregon State University. "The general principles of the test are applicable anywhere," concurs James Walworth, Ph.D., a soil scientist with the University of Arizona's Cooperative Extension in Tucson, "but the specifics will differ."
Scientists warn gardeners not to overemphasize results from one or two steps, but to consider the test as a whole. For instance, "sandy soil is pretty easy to work," says Mark Williams, Ph.D., an assistant research scientist of soil microbial ecology at the University of Georgia in Athens, Georgia, "but the soil may not have other components of soil quality."
You can do all 10 steps during the active growing weeks in spring. You can test for soil structure and tilth, compaction and plant residue, year-round. Check various locations in the garden for the broadest picture possible. The more detail you have, the more accurate and reliable the results.
When the soil is neither too wet nor too dry, dig a hole 6 to 10 inches deep. Separate an intact section about the size of a soup can and break it apart with your fingers. Determine whether the soil is cloddy, powdery, or granular. Ideally, your soil should be made up of different sized crumbs that will hold their shape under slight pressure. Crumbs, or aggregates, as soil scientists call them, that break apart only with difficulty mean your soil is too hard.
Why it's important
"Soil rich in organic matter tends to form relatively round aggregates, which leads to porosity," says Tom Thompson, Ph.D., a professor of soil science, also at the University of Arizona. Open, porous soils allow the free movement of water and oxygen, he explains, so plants can develop strong, healthy roots.
Plunge a wire flag vertically into the soil at different locations. Mark the depth at which the wire bends. The sooner it bends, the more compacted the soil. A foot or more of easily penetrable soil is ideal.
Why it's important
Compacted soil inhibits root growth and water availability, and keeps earthworms and other vital soil fauna from circulating freely.