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The dirt on getting better soil

There is nothing more coveted by gardeners than perfect dirt. Crumbly, loamy soil that’s rich in organic matter and teaming with earthworms. It doesn’t come easy here in Western Pennsylvania (or anywhere, for that matter!), but it’s worth fighting for.

I know you may find it hard to believe, but our native soil isn’t half bad. Yes it’s clay-based, but that isn’t necessarily a bad thing, as you’ll come to learn in a bit. The problem is that many of our gardens are built on land that was stripped of its topsoil during the home’s construction. Or, the soil has been nutritionally depleted by the grass and other plants growing there, and Mother Nature hasn’t been allowed to replenish it with rotting leaves and the natural decomposition of other debris because we pick it all up every fall.

In order to understand how to fix our depleted soil and turn it into a gardening Mecca, you first have to understand what soil is comprised of.

Every sample of soil, be it a teaspoon or a truck load, contains relatively the same things. About 50 percent of the sample is mineral fragments, derived from rocks that have broken down over millions of years. These fragments come in three basic sizes: the largest is sand, in the middle is silt and the smallest particles are clay. The U.S. Department of Agriculture classifies a soil based on how much of each size particle it has.

As I mentioned before, in our region, we have primarily clay-based soil. This means we’ve got a high percentage of clay, and that’s why our soils stay waterlogged in the spring and turn to concrete in the summer. The good news is that clay is relatively high in nutrient content, and we can actually improve it. The bad news is that clay particles are very sticky and tend to mat together. That’s why when you squeeze your soil into a ball, it stays in a clump. Sandy soils, on the other hand, are low in nutrient content and are much more difficult to improve.

Another 35 to 45 percent of the soil sample is a mixture of water and air. These two occupy all the spaces between the mineral particles. Because we have a clay-based soil, these spaces are extremely small, and that’s why our soil doesn’t drain easily. Think of sand, whose particles are big. The spaces in between the sand particles are huge and that’s why sandy soils drain so quickly. It’s like putting water through a colander: One with a few big holes will drain a lot faster than one with hundreds of very tiny holes.

The rest of the soil sample (1 to 6 percent) is organic matter. Unfortunately, this tiny percentage is the most important part of your soil. Organic matter is derived from dead and decaying plant and animal matter. It is pretty much anything that was once alive.

This organic matter binds your soil particles together and changes the way they aggregate, or clump. It gets in between the clay particles and separates them, holding them apart on the microscopic level and allowing water to drain more easily through them by opening larger channels. Organic matter is high in nutrients and is a wonderful source of food for your plants. It’s the primary food source for the beneficial soil microbes that break it down into elements your plants can readily use to grow.

So, if you want good soil in your backyard, you’ve got to add organic matter … and lots of it: compost, humus, well-rotted cow or horse manure, mushroom soil, decomposed leaves or leaf mould. Top soil purchased in bags or by the truck is not organic matter. Work organic matter into your garden on a regular basis; twice yearly, if possible. I add at least 3 inches of some type of organic matter to all my gardens every year. In the vegetable garden, you can till it into the soil every spring. In flower and shrub beds and borders, use it as a mulch by adding it to the top of the soil.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is www.jessicawalliser.com.

Send your gardening or landscaping questions to [email protected] or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.


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