How to Manage Grey Clay Soils

Grey clay can be transformed into fertile soil.

Any successful gardener will tell you that the secret of a bountiful harvest is in the soil. Unfortunately, few gardeners are blessed with perfect soil. Soil may be too rocky, sandy, compacted or composed of dense clays. If you're trying to manage gray clay soil, found throughout many parts of the midwestern portion of the United States, don't be discouraged. You can turn your infertile clay into fertile, nutrient-rich organic soil.

Things You'll Need

• Gypsum
• Organic compost
• Organic mulch
• Dolomite
• Sand
• Garden tiller

Instructions

Test the Soil

1. Perform a soil test to determine the nutrient content and pH levels. To prepare a sample, dig several holes randomly (about 10 to 20 feet apart in a checkerboard pattern) across the landscape. Dig each hole 6 to 8 inches deep. Disregard the soil. Move back about 1 inch from the hole and take a clean 1-inch slice, 6 to 8 inches deep. Place the slice in a clean plastic bucket. Repeat this procedure at each test hole, adding a 1-inch slice from each hole to the contents in the bucket. Thoroughly mix the samples, breaking up all clumps and removing rocks. Spread the sample material out on layers of newspaper to dry.

2. Place 1 pt. of the dry mixed sample materials in a sealable plastic bag. Send the soil sample to a state extension office, commercial testing laboratory or the agricultural department of a college or university. Or, use a basic do-it-yourself soil testing kit.

3. Test soil compaction. Insert a compaction test rod inserted in the soil and apply steady, firm pressure. If a hardpan or resistant clay layer is encountered, make notes of the depth and location in the yard so you know how deep you'll need to cultivate. Gray colored clay indicates poor drainage. (If the clay layer is not too deep or too thick, you can remove the clay and replace it with topsoil. If this isn't feasible, amend the soil as recommended from the results of the soil test.)

Cultivate and Amend the Soil

1. Broadcast 30 lbs. of gypsum over every 1,000 square feet of land to be cultivated. Gypsum is effective in areas where the soil is quite salty. The sulfate contained in gypsum helps to acidify the soil. Use a garden tiller or tractor to cultivate the soil. Till repeatedly, cultivating both vertically and horizontally across the soil surface. Till as deep as possible. As you turn over the soil, remove large rocks and roots.

2. Add dolomite to the soil. If soil tests reveal that pH levels are less than desirable, an application of dolomite (calcium and magnesium) will raise the pH. Apply 5 lbs. of dolomite for every 100 square feet of garden plot to increase the pH level by one point. Cultivate well.

3. Spread a 6- to 8-inch layer of organic compost on top of the soil. Organic compost will increase the nitrogen and phosphorus levels in the soil. These nutrients act as stimulants to plant growth and root development.

Allow the Soil to Decompose

1. When establishing a new garden plot, perform the previous steps in the fall and allow the soil to rest until spring. Cover the cultivated ground with a heavy layer (12 to 18 inches) of organic mulching material. Use any combination of aged, non-treated sawdust, dead leaves, grass clipping, kitchen food prep waste, straw, pine bark, shredded newspaper, cardboard or manure from herbivores--cows, sheep, horses, lamas or goats. The addition of organic matter of almost any kind greatly improves the structure, texture, fertility, drainage and functionality of soils. Water the material well until it's thoroughly saturated. Cover with a layer of thick, black landscape plastic. Secure the plastic with rocks or planks and leave it covered until spring.

2. Uncover the garden plot after all danger of frost is past. Broadcast another 20 to 30 lbs. of dolomite on the soil's surface.

3. Cultivate the dolomite and the decomposed mulch layer into the soil in the spring. Till repeatedly to ensure that the material is worked into the soil well.

Tips & Warnings

• When taking soil samples always make sure the digging tools and bucket are clean. Residue from fertilizers, pesticides and herbicides will contaminate the sample.

• Do not cultivate or work with clay soils when the clay is wet. Clay compacts easily, so don't walk or drive equipment on wet clay soil.

References

• North Carolina State: Master Gardener Guide
• Bachmans.com: Garden Care--Working With Clay Soils
• Garden.org: Garden Calculator--Limestone