When Improving Clay Soil Requires Extensive Dirt Work

At times improving clay soil is a difficult process. I have been to places where "red/orange" is the only color the soil seems to be. It is heartbreaking, but there is help for those who really want to correct it.

Clay soils come in a variety of textures and colors. From Oklahoma's reddish orange clay to the darker gumbo clay of the deep south. There is even an edible white clay, but that is a different story.

The most radical improvement will involve removing the top layer of clay soil and replacing it with good topsoil. This is especially true if you live in a part of the world where clay seems to be the only soil you have. A less radical approach is the addition of topsoil incorporated by topdressing and core aeration. Click here for step by step information on Top Dressing Lawns.

There are also other reasons for removing the top layer to improve clay soil. Home builders are notorious for burying your good topsoil, while leaving the clay sub-surface layer on top. Regardless of your situation, if complete lawn restructuring is your chosen method for improving clay soil, here is where you will find some sound advice.

Clay soil has some advantages. The most notable is that it holds water and resists erosion well.

It also has disadvantages that could necessitate improving clay soil where you live. Below are some of the disadvantages of clay soils.

  • Clay soil compacts easily.
  • Compacted clay soil will hold less oxygen and water.
  • Clay soil can bake in the hot sun becoming as hard as a rock.
  • Root penetration is more difficult in clay than in lighter soils.
  • Clay soil is a mess to work with and sticks to everything.

Before Any Work Begins

First, know that sometimes improving clay soil can a difficult process. Please know that it takes skill and knowledge to do the job right.

If you do it yourself, you may need the use of a tractor and dump truck. Tractors you can rent, but not usually dump trucks, which often require a class b commercial license. You need knowledge of rough grading, forming a subgrade, sprinkler installation (if you want them), etc.

You also need to know how your improvements could affect your neighbor’s lawn and the flow of rain water. You may need to get permits before you start any work, so be sure to check first.

Important Legal Information

In many states it is illegal to grade or add to your lawn so the finished work raises the level of your lawn making it higher than your neighbor's lawn. If you cause water to run into or flood your neighbor's lawn (where it didn't before the work was performed) you may be legally responsible to fix it.

Some people may find it best to hire a professional. Improving clay soil can be overwhelming for a beginner. However, many homeowners have done this successfully as long as they follow sound practices. If you want to do the work, but have some reservations, consult with a professional for advice before work begins.

Important: Please Read

The following advice is not a step-by-step guide on improving clay soil where extensive work is involved. Nor is this a complete How to Improve Clay Soil guide for removing the top layer soil. Improving clay soil in each lawn presents its own challenges and there is no single formula that will fit them all.

  • Tree location and tree roots need to be considered. Most tree roots are in the top 12 inches of soil. Removing all the topsoil from around a tree could possibly injure or even kill it. If you are not sure what may happen or how much soil to remove, contact an arborist for advice first.
  • Is there a slope to your lawn? What type of foundation? Do you have a basement? Are the basement windows at ground level? Disturbing the soil around the basement will effect the natural flow of rain water. Loose soil collects instead of allowing it to drain away.When a pipe broke at my house and needed to be replaced, they dug next to the basement wall about 4 feet deep. The next heavy rain we were shocked to find that many gallons of clay-tinged water flooded into the basement adjacent to where the hole was dug.
  • However, modest changes for improving clay soil can be performed when sound principles are applied. Again, if you are in doubt, always consult a local expert before you begin any work.

Considering if Soil Removal is Necessary

You will need to determine if the removal of any soil is actually necessary for improving clay soil at your site. You may determine that you can get by without removing any. Here are a few things to look for:

  • Is your lawn surface well below your home entry floor? In other words, even after spreading several inches of topsoil, will the lawn still be below your home's ground level floor? The bottom of your entry door must be above the new soil height.
  • Remember that additions of several more inches of topsoil placed over the roots of trees can cause damage to trees. The roots are in the position needed to get the right amount of water and oxygen. Piling more soil on top of roots alters gas and water intake. The damage will often appear in the tops of the trees first. Severe cases can kill the tree.
  • If any digging is involved, first call your phone company, electric company, and other utilities to mark any buried lines. In most states it is the law and provide a service such as "dig-rite" that will send someone out free of charge.
  • You must consider how adding several inches of topsoil will affect sidewalks, driveways, and in-ground sprinkler systems. Your sprinkler heads are designed to pop up above your grass.
  • When the top six inches of clay soil needs to be removed and replaced with topsoil, water will percolate through the topsoil and flow along the clay subgrade. (Explained in more detail below). Consider if there is anything that would stop the natural flow of water and cause it to pool below the surface. This may create problems for you later.
  • Be sure the slope allows water to drain away from the house. I know this from experience after purchasing a house with a very poor grading job. We needed waders to walk from our house to the car after a rain. (Not really, but our shoes did get very wet.) The subgrade slope and topsoil surface slope needs to be the same.

Understanding the Subgrade

Unless you are experienced at improving clay soil where extensive work is required, you might consider hiring a professional. Here’s why.

After you remove the top layer of soil, the surface you are left with will look pretty rough. There will be holes, low spots, raised areas, etc. Before the topsoil is brought in, the surface will need to be carefully smoothed out. This lower surface is often made of clay and is called the subgrade. It forms the foundation for the topsoil and must be graded just right so the water drains properly. The subgrade will have the same slope and contour as the surface will have after the topsoil is added.

The most important thing: The slope of the subgrade will need to be sloping away from the house. It needs to be as smooth as possible. If the subgrade is made too flat or slopes back toward the house, you will have problems when it rains. The rain water will often follow the subgrade surface and could pool in low spots, against the house or under foundations if it is graded improperly.

Once the subgrade is formed correctly be sure to remove any rocks, wood, or trash from the surface. You will find that some contractors will bury sheetrock, lumber, or other material under that load of topsoil because it is easier than hauling it away. However, they cause their own problems.

Problems that can occur with burying objects.

  • "Fairy Rings" occur where buried wood is being consumed by wood destroying fungi. The wood may be a few inches deep to a foot or more. As the wood decomposes, a dark green circular ring or partial ring appears in the grass. The ring stripe may be dozens of feet long. This ring is often accompanied by mushrooms. The mushroom are the fruiting bodies of the fungi. The bottom of the mushroom cap is where the spores are released into the air so the process can begin somewhere else.
  • These fairy rings can last for years returning during the summer months. Grass in the fairy rings tends to grow faster than the rest of the grass and the mushrooms can be unsightly. This is because the fungi is breaking sown the wood into usable nutrients. A fairy ring can be a full circle twenty feet or more wide, but is often only a partion of a circle. The green circular stripe is generally around 18 inches wide.
  • Large flat rocks, buried sheet rock, or other debris can cause dry looking spots in the lawn. The grass roots are not able to penetrate the soil over the buried material. These spots will often be most severe in summer months.
  • If you live in a rocky area you may need to use a rock rake to work over the surface. This will loosen any rocks larger than a golf ball that can later be removed.

Applying Topsoil To the Subgrade

After the rough grading, the next step of improving clay soil is to bring in the topsoil. The topsoil should be six to eight inches thick for your grass to develop the best root system. Spread the topsoil evenly over the prepared subgrade or graded surface.

If you performed a soil test on the topsoil, this is the time to apply any corrective amendments, such as lime, compost, phosphorus, etc. Fertilizers can be raked into the surface easily as well.

A riding lawn mower and a pull behind lawn roller will come in handy. Rolling the lawn will not compact the lawn greatly and will help show low and high spots quickly. The lawn will always settle, but by rolling the lawn first you can instantly see where extra raking needs to be done.

You can also use this stage in the renovation process to install any drainage tiles, retaining walls, sprinkler systems, install planters, or for planting trees.

With your project of improving clay soil almost complete, the lawn is ready for seeding or sod.


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