How To Improve Clay Soil

Home builders are notorious for stripping away the topsoil before building begins. If the home has a basement, the lot is covered with the excess clay that was removed during construction. The photo to the right shows red clay from basement construction spread over the topsoil. The majority of the planting surface is now clay.

Amending clay is not as hard if it is done before the grass is planted. After the grass has become established, the homeowner is presented with a different set of choices.

Problems and benefits of Clay

A certain amount of clay in soil is not a bad thing. Clay has excellent water holding capabilities and can be very fertile. However, the problems of excessive clay can easily outweigh the benefits.

Below are a few problems associated with clay soils.

• Clay is difficult to penetrate which makes it hard for roots to become established.
• Clay soil tends to be alkaline, which makes iron unavailable to plants.
• Clay compacts easily reducing the amount of oxygen to the roots.
• Clay can absorb and trap water for extended periods.
• Clay can also cause puddling and drainage problems.
• Can become rock hard when dried.

Amending Clay soil and How Much To Apply

Before adding organic matter, you will need to know how much to apply. First, you will need to know how much organic matter is already in the soil. Submitting a soil sample to be tested will give you that information. This link will help you understand how to conduct a Soil Test. After you receive your test results, come back here for help interpreting the Soil Analysis Report.

Examples of Actual Pounds in Relation to Percentages

(If you are on the metric system, this page offers easy conversion for the figures below: Weights and Measures, Metric Conversion)

The average soil test indicates that most lawns have between 2% and 6% organic matter. Many researchers agree that 5% to 6% is ideal for most lawns.

To get an idea of how much organic matter 2% actually is, check out the facts below:

• Topsoil is generally considered to be the top 6 inches of soil. This is the maximum depth many soil tests are based on.
• One half acre (.5 acres) of topsoil weighs approximately 1,000,000 lbs. (one million pounds)
• If a soil tests indicates you have 2% organic matter in your half acre of topsoil, that would equal approximately 20,000 lbs (twenty thousand pounds) of organic matter.
• To increase the amount of organic matter by only 1% would require 10,000 lbs of organic matter spread over your half acre. To bring it to 6% would require 40,000 lbs of organic matter.
• If your lawn is one quarter acre (.25 acres) in size, simply divide the pounds of organic matter listed above by 2. For example, it would take 5000 lbs (five thousand pounds) of organic matter to increase the level of organic matter from 2% to 3%.

It is a lot more than people think. Obviously, it is usually not practical to apply that much at one time. If you have poor soil, the best way to incorporate the amount of organic matter needed to truly improve your soil will require a roto-tiller to work it in.

Note: Do not roto-till clay after a rain because it will destroy the clay structure, further compacting the soil. Wait until the soil has had time to dry.

An easier method, if possible for you, is to simply apply 6 inches of quality topsoil over your existing clay soil and plant your lawn in that. Be sure you prepare and level the site before planting.

For those who are planning to cover their lawn with several inches of top-soil, please read the page When Improving Clay Siols Requires Extensive Dirt Work

Amending Clay Soil For Existing Lawns

It helps greatly to core aerate the lawn before topdressing. Core aeration pulls out a plug of soil approximately ¾ inches wide by 3 inches long. Pass the aerator over the grass several times in different directions. It will seem like you are over-aerating, but you are not. If the soil is largely clay, remove the cores before topdressing. Once you begin top dressing, allow the organic matter to fill the holes. This gets the amendment down into the soil instead of only on the surface.

There are a few companies that specialize in top dressing lawns, but not many. Rental equipment designed to spread organic matter on lawns is just as difficult to find. Using a wheel barrel and a shovel to scatter a thin layer is still the most common method used.

Organic Soil Amendments

There are a number of natural soil amendments on the market that claim to help relive clay soil compaction. Some products work well, while others don't.

Turface is a product developed by the professional sports industry for use on baseball fields to relive compaction, absorb excess moisture after rain, and to help airify the soil. It is available for home lawns and gardens as well.

It is a product that has proven itself and is now used in nurseries, container plants, vegetable gardens and even in the bottom of fish tanks. It is best when blended into the soil, but some products are designed to be broadcast on the surface.

Humic Acid is also used to relive compaction. It is a term that describes the bio-chemically active ingredients of humus and is derived from many decomposed organic materials. In the U.S., the best sources of humic acid is found in coal around Arizona.

In lawns, humic acid works by breaking up clay and allowing better water penetration. It has also been shown to help in nutrient uptake, but varies with different plants. It helps with water retention in sandy soils as well.

Do not use sand to blend into clay soil as an amendment. Even though it is given as advice in some articles, it will have an opposite affect by making the clay rock hard and almost impossible to work with. For sand to be effective, it must be at a rate of over 50% of the volume of clay. That would equal a tremendous amount of sand for a home lawn.