Help! My clay soil is stunting the growth of my plants. I’ve amended the soil with compost and manure. Is there a another method of conditioning the soil that you can recommend?
First and most important, it appears mulching is the best organic solution for conditioning clay and heavy soils. Organic soil conditioners include compost, well-rotted animal manures, and natural fertilizers. Planting green manures such as clover, rye grass, or vetch are also effective for breaking up large clods in clay soil over time.
Sheet composting – laying compost over the entire area to be worked and using a fork (or rototiller) to work it into the soil to a depth of 2-4 inches – is cited by the resources listed below as an efficient method of soil conditioning. Both books listed below recommend repeating this process at least twice a year, in early spring and in late fall.
Secrets to Great Soil [by Elizabeth P. Stell, 1998, (pbk)] and
The Gardener’s Guide to Better Soil [by Gene Logsdon, 1975, (pbk)]
The Saving Water Partnership (the City of Seattle and other government entities) has a website full of information about improving soil.
The site includes Growing Healthy Soil.
Current thinking contradicts the notion of working compost or other amendments into the soil, as explained in a March 31, 2010 Garden Professors blog post by Professor Linda Chalker-Scott of Washington State University Extension Horticulture. She specifically takes issue with the “Growing Healthy Soil” information linked above. Here is an excerpt:
“Not only will extensive digging or rototilling destroy any soil structure you might have, it will also take out the roots of any desirable plants in the vicinity). […] improper soil amendment can cause serious problems such as soil subsidence, perched water tables, and nutrient overloads. This last point is especially important to anyone living near aquatic ecosystems, since excess nutrients always end up in the water.
Before you plant this year, find out what your soil needs before amending it. And remember that mulching is the natural (and sustainable) way to add organic matter to the soil.”