Organic gardeners like to say they're growing soil, not plants. The basis of a healthy garden is soil and the life in the soil. To evaluate a soil, you can feel it, smell it, look for worms, and see if plants growing in it seem healthy. Clay soil is a wonderful soil to start with because it can hold onto lots of minerals and release them to plants.
But ultimately, whether you've been gardening a few years or starting out, you may want a soil test.
Two new books that talk about amending your soil to produce nutrient-dense food have recently been published, and both advocate soil tests. Though their approaches are different, they are complementary. Both stress the importance of adding minerals to the soil, and both recommend far less compost than many organic gardeners are accustomed to using – as little as 1/6 to 1/90 inch per year. Both avoid dolomite lime, because its calcium/magnesium ratio is bad for most soils, and instead recommend calcitic lime (aka agricultural lime). Both also discourage gardeners from adding too much of anything without a soil test, because even moderate amounts of some amendments can throw the soil chemistry out of whack.
In his book The Intelligent Gardener: Growing Nutrient Dense Food (New Society, 2012), author Steve Solomon (with Erica Reinheimer ) takes a more linear and quantitative approach, once you get past his opinionated and curmudgeonly first chapters. He recommends a specific $20 soil test from Logan Labs. Once you send off your soil samples and get the numbers back from the lab, you can analyze your soil-test results by completing worksheets, conveniently available online at http://tinyurl.com/c45cfsb, to determine what amendments to add. He explains in detail what amendments to use and how to use the worksheets. He also includes his formula for Complete Organic Fertilizer, which he considers a reliable alternative if you can't do a soil test.
But soil chemistry is as far as he goes. If you're more interested in the life in the soil, and don't mind a more qualitative approach, the next book is the one for you.
Phil Nauta, in his book Building Soils Naturally (Acres USA, 2012), gives a more detailed and nuanced discussion of stimulating the soil food web, covering soil biology as well as soil chemistry. He includes cutting-edge topics such as brix testing, seawater, mycorrhizae, paramagnetic rockdust, and culturing EM (essential microorganisms). One of his most valuable recommendations is adding rockdust to the compost pile, where it can get chelated with organic matter to make the minerals more biologically available to plants. The most useful part of the book is a 5-page summary of his recommendations at the end.
He recommends adding smaller amounts of minerals 2-4 times during the year, rather than all at once: Plants and microbes need continual access to a small amount of nutrients rather than everything at once. He also stresses the use of molasses and other biostimulants to unlock soil nutrients.
For gardeners who don't do a soil test, Nauta says it's rare to find a soil that wouldn't benefit from 1/2 pound of calcitic lime per 100 sq. ft. He also gives a recipe for a foliar spray he recommends using with new seeds and transplants, and throughout the garden every 1-4 weeks.
© 2013, 2014 Tanya Kucak