Regional Gardening Reports :: National Gardening Association

In the Garden:
Upper South
April, 2010
Regional Report

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A beautiful garden is the result of caring for soil as well as the plants.

Get To Know Your Soil and Learn To Love It

Learning about soil isn't the most sexy or exciting part of gardening, not like reading the glowing descriptions of wonderful new plant varieties, but when you have at least a basic understanding of soil, then that rare, new whatever is much more likely to grow and thrive. If I had a nickel for every time someone said to me that they had bad soil, I'd be a rich person. Certainly, soils that have had to endure construction are usually not in good shape. But the vast majority of soils can be amended and improved, although sometimes you may have to compromise on what you can grow. In fact, matching plants with your site characteristics is critical to a successful planting.

Assess Your Current Soil Conditions
First and foremost, get a thorough and complete soil analysis from a reputable soil testing laboratory. An easy way to find one is to contact your county's Cooperative Extension Service office, usually listed in the phone book under county offices. Another way is to visit the web site of the National Sustainable Agriculture Information Service and their article on alternative soil testing laboratories at While you're at their site, read through the entire article, which has valuable information on soil, organic matter, fertilization, and soil health. A good soil test provides pH, organic matter, cation exchange capacity, texture, and nutrient concentration. The laboratory should provide you with recommendations for ways to amend the soil to deal with any deficiencies indicated by the testing. Most Cooperative Extension offices have pamphlets that explain how to take a soil test. Many state Cooperative Extension web sites will also have that information. For example, here is one from Kentucky,

Try to select a lab that also does a mechanical analysis of the soil texture. Soil texture refers to the percent of sand, silt and clay content in a given soil. The ideal topsoil generally has 40 to 65 percent sand, 25 to 60 percent silt, and 5 to 20 percent clay.

Of the major nutrients in the soil- nitrogen, phosphorus and potassium- nitrogen is the most difficult to accurately test for, as the concentration varies with temperature, moisture, and root activity. You'll know if nitrogen is limited if plants growing in the soil show uniform yellowing of leaves. A fertilizer higher in nitrogen than the other two elements should alleviate the problem. Regular applications of organic matter also help to maintain nitrogen levels in the soil.

The Importance of Organic Matter
Organic matter is the "magical" ingredient in soil, able to improve both sandy and clay soils. An organic matter content up to 10 percent is suitable for an amended soil. Depending on the current condition of your soil, this means spreading a layer 1 to 3 inches deep on the soil surface, then tilling it in. In using organic matter to improve soil, think in terms of improving entire beds rather than planting holes.

The best choice for the organic matter to improve you soil is compost, either homemade or purchased. There are pros and cons to both choices. Your own may contain weed seeds if it did not heat up properly, while purchased compost may not have had much green matter incorporated into it or may contain pesticides.

The devil is in the details. Think through what works best for you and your situation. As organic matter breaks down in the soil, it's crucial to annually apply an organic mulch.

Should You Buy Topsoil?
Although it may sound like a panacea, bringing in topsoil is not without its perils. For one thing, be sure to evaluate the soil quality before it is delivered, and remember that "brought-in topsoil" is not the same thing as naturally occurring topsoil. The purchased topsoil should be free of large pieces of plant material, large stones, and foreign objects, such as glass, paint chips, and plastic. Gravel content should be less than 10 percent. When spreading purchased topsoil out over a garden area, it's important to intermix it with existing soil. This will help water movement and root penetration. Do not cover tree roots with any more than 1 inch of new soil.

Soil and Water - The Crucial Balance
A well-drained soil has both water-holding capacity as well as a good complement of air spaces, necessary for the healthy function of all but aquatic and bog plants. Most often, soil compaction is the reason for poorly drained soil. Unfortunately, soil compaction is usually part and parcel of new house construction. To determine if your soil has adequate drainage, you can perform a simple test.

In an area where you want to have garden plants, dig a narrow hole 12 to 18 inches deep and fill it with water. Let it drain, then refill. Note the number of hours it takes for the water to drain from the hole, perhaps noting the water level at various times. Bottom line, the longer the water remains in the hole, the poorer the drainage. If water remains in the hole for over 24 hours, then drainage issues must be addressed before attempting to garden. A plan must be developed to move the water, via drain tiles, trenches or culverts, to an appropriate place.

Final Admonitions
Even the best of soils responds to care and attention. Well-cared-for soil will return the favor in spades. In getting to know your soil, I have a few "bottom line" tips. First, it's hard to love something called "dirt." Dirt is what is in my house. Call it instead by its proper name: soil. Next, don't walk on bed and borders any more than you have to. Consider getting a short board you can lay down and stand on as you work in your garden beds. The board will spread out your weight and lessen soil compaction. Adding a high-quality organic mulch every year is invaluable. My own personal favorite is dark hardwood mulch. Remember, you want it to decompose. And never, ever work soil when it's wet. Your soil will thank you.

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