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PAL Questions: 1 - Garden Tools:
Part of my yard has clay close to the surface. In addition to heavy and yearly amending with compost and other organic materials, I have heard that adding gypsum is helpful for breaking up heavy clay. Any thoughts or suggestions on this?
One of the most reliable resources I've found on how to amend soil is Prof. Linda Chalker-Scott, of Washington State University Extension. According to her very useful website on horticultural myths, gypsum does improve clay soil but is not the best choice for most home gardens. Here is an excerpt:
"With the exception of arid and coastal regions (where soil salts are high) and the southeastern United States (where heavy clay soils are common), gypsum amendment is just not necessary in non-agricultural areas. Urban soils are generally amalgamations of subsoils, native and non-native topsoils, and--in home landscapes--high levels of organic and non-organic chemical additives. They are also heavily compacted and layered (and gypsum does not work well on layered soils). In such landscapes, it is pointless to add yet more chemicals in the form of gypsum unless you need to increase soil calcium levels. This nutrient deficiency can be quickly identified by any soil testing laboratory for less than a bag of gypsum costs. (If you need to improve sulfur nutrition, it's wiser to use ammonium sulfate). To reduce compaction and improve aeration in nearly any landscape, application of an organic mulch is more economically and environmentally sustainable."
Washington State University says the following about gypsum as a soil additive:
"Gypsum is calcium sulfate. It is not a substitute for lime, and has little effect on soil pH. Gypsum only improves structure in soils that have extremely high sodium contents (rare in the Northwest)."
It sounds to me as if your practice of amending the soil with compost and organic matter is the best approach.
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April 19 2012 16:02:30