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Gardening in the Sierra Foothills with Carolyn Singer

Clay soil in good tilth makes gardening a pleasure
Dig in amendments & enjoy the change

by Carolyn Singer
March 27, 2010

Filoli GardensThe most exciting part of my garden is the soil. After more than three decades of adding amendments and mulches, I can enjoy the ease of digging in clay loam, soil in good tilth. However, there are many areas of native clay soil on my land, reminders of just how difficult it is to dig in unimproved garden soil.

The amendment I have used most widely is my own compost. I build piles closest to where I'll be using it. With the fall cleanup in the vegetable garden, I usually build a compost pile on one of the garden beds. Layers of spent tomato plants, weeds, leaves from my deciduous trees, and vegetable waste from my kitchen are covered with a sprinkling of colloidal phosphate and oyster shell, then topped with two to three inches of organic poultry manure.

Use manure that has been CCOF (California Certified Organic Farmers) approved. Ask your vendor about its origin. Or, if you are buying it by the bag, read the label.

Poultry manure may be high nitrogen, too "hot" for young plants, but excellent used for the compost pile. By the time you spread out the fall-built compost pile in spring, you can plant starts of broccoli, lettuce, chard, and other spring greens directly into the compost without delay.

I make compost piles all summer long within the vegetable garden, primarily using the weeds I have pulled, some straw, and my kitchen waste. The summer piles are usually finished within a month, and the resulting compost may be spread as a mulch. Irrigation water moving through the mulch creates compost tea, stimulating root growth.

soil builder cover cropSometimes my compost is spread over a cover crop I have cut down with a sickle. This is one approach to sheet composting. The compost helps the cut greens to decompose, and no digging or "turning in" the green manure is necessary.

"Tilth" is a word so uncommonly used that my word processor does not recognize it. And yet, among people who take soil seriously, it is an important term. When our clay soil is in good tilth, it is vital, an aggregate of clay and humus rich in microbial activity, and perfect for gardening. Adding lots of compost is one way to create and maintain soil in good tilth.

Burbank Gardens in Santa Rosa CAAdding compost and then sowing a cover crop adds even more vitality to the soil. Roots of the cover crop break up the clay soil and add humus. Cover crops may be sown any time of year to build soil. If your soil is still high in clay content a good summer cover crop is buckwheat. Sow as soon as danger of frost is past in spring, and cut it down in about two months, before it goes into a seed stage. Cover the cut greens with two inches of compost. There will still be time to sow summer "soil builder" cover crop and have perfect soil for planting broccoli in September and garlic in October.

Mushroom compost (again CCOF certified) is another amendment that will build soil good tilth. It is often low in nitrogen, the composting process already having taken place, and safe to use right after adding to your soil. When I have a pile delivered, I do a very unscientific test. I dig into the pile about 18 inches. If the material feels warm, I test it every few days. Often the heat that occurs right after delivery is simply the addition of air reactivating the composting. This what occurs when you turn your compost pile. When it is no longer warm, the mushroom compost may be used for planting.

Burbank Gardens in Santa Rosa CAI do not rototill my garden, and I do not turn my compost piles. If soil has been damaged by winter rains (in areas where I failed to sow a cover crop in the fall), I do dig amendments into the top few inches of the garden bed. More important to me is to build tilth every year, adding as many organic amendments as possible, without disturbing the soil. As soil improves, gardening gets easier.

©2009 by Carolyn Singer. All rights reserved.

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