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Originally published Friday, March 18, 2011 at 7:00 PM

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A simple soil test can help improve garden

The Gardener Within: Good, rich soil is the living heart and soul of gardening. But figuring out how to get it takes a bit of work.

Scripps Howard News Service

As a seasoned gardener, I've gained an almost reverent respect for soil. It can make or break any garden. Dirt, on the other hand, is what you clean from under your fingernails. Healthy gardens grow in soil. Good, rich soil is the living heart and soul of gardening. But figuring out how to get it takes a bit of work.

Soil is made up of minerals, rock broken down by time and weather into three general particle sizes. The first, sand, is relatively huge. It doesn't hold water or fertilizer very well but has terrific porosity, or air space between the grains. Next is silt, about the size and consistency of dust. Water runs off it before soaking in, but once it's saturated it holds water and nutrients better than sand. Finally comes clay. Dry, it shrinks, cracks and repels water. Wet, it's swampy and doesn't give up its nutrients easily.

It is important to have all three types of particles in your garden soil. The different sizes of each create essential space for air and water to exist as well. Imagine basketballs, tennis balls and marbles, all sharing the same space. It is easy to see how air and water can find their way in and through the spaces in between.

The Jar Test

To find out what proportions of sand, silt and clay you have in your soil, try the simple jar test. Start with a jar with a tight-fitting lid. A mayonnaise or canning jar works great. Fill it about halfway with soil from your yard or garden. Add water to the jar until it is almost full. Secure the lid and shake the jar vigorously. Set it down and let the contents settle overnight or longer. What you will find is that the soil has separated into three distinct layers.

The first layer is sand. These are the largest particles. Because they are the heaviest, they settle to the bottom first. The second layer is silt. Silt is a combination of sedimentary materials that are smaller than sand and larger than clay. By weight, they settle in the middle. The third layer is clay. It is the finest and lightest of the three most-solid components of soil.

Now you can easily see proportionately just how loose and sandy or dense and full of clay your soil is. More importantly, it gives you the clues on how to approach amending it for ideal conditions.

The Squeeze Test

Regardless of the current soil structure, you can change what you already have. The goal for amending soil is for it to pass what I call the "squeeze test." If you were to squeeze a handful of ideal garden soil, it would bind together and hold its shape. However, it would also be loose enough so that the lump would crumble or break apart easily if you ran your fingers through it.

Improving Sandy or Loose Soil

In sandy soil, water and nutrients pass through the root zone too quickly. The goal is to increase soil's capacity to hold water and nutrients. Adding organic material helps the sandy particles stick together into aggregates of various sizes. The net effect is that water and nutrients have a chance to bind to these aggregates rather than quickly leaching out. Peat moss and compost are common amendments for improving sandy conditions, but any organic material will help.

Improving Dense or Compacted Soil

Soil that is too dense or compacted retains too much water and too little air. Here the goal is to loosen it. Adding organic material — such as composted bark, wood chips, composted manure, shredded leaves or compost — helps to achieve the proper balance. In dense soil, the addition of organic material of various particle sizes allows the smallest particles of clay to bind to them, creating larger aggregates. The result is more space for air and water, and soil that is more sustainable for essential living organisms that promote soil health. Do not add water-retentive material such as peat moss or coir.

Joe Lamp'l, host of "Growing a Greener World"on PBS, is a Master Gardener and author. For more information, visit www.joegardener.com.

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