Amending Clay Soil

Unfortunately, many of the plants that we want to grow will either struggle or fail to survive in clay. So the next option is to make changes to the soil. If you opt to try to change and amend the soil, it is very important to understand that it will take lots and lots of the right type of amendments. Just adding a bag or two of sand or manure will only make the situation worse. The key to amending clay soil is to amend a large area and use enough coarse sand and coarse organic matter. Avoid trying to change a small area. Plants will have a difficult time making the transition to the surrounding clay soil, effectively limiting their growth to the amended area. And remember not to work clay soils while they are wet. Two of the best amendments for clay soil are coarse sand and coarse organic matter such as compost. Coarse sand is also sometimes called builders' sand. The particles are relatively large, especially when compared to the finer sands used for sandboxes.

Finer sands may actually make your problem worse. There are lots of types of organic matter available for gardening but not all of them will help improve clay soil. It must be coarse. Avoid fine-textured material such as peat moss or the packaged manures. If possible, find a source for a coarse compost or aged manure. Check with your city to see if they have a compost site for leaves yard waste.

First, calculate the area you are amending. Length x Width = Square Feet. Ideally, you should use equal parts of coarse sand and coarse organic matter to amend the soil, but extra sand can be used if necessary. You will need to cover the area with a 3-4 inch layer of organic matter and a 3-4 inch layer of sand. Bagged products won't be practical, since they usually hold a half cubic foot or less and would only cover a couple of square feet. Look for a source of bulk material. It will probably be measured by the cubic yard (27 cubic feet). The general rule is that one cubic yard will cover approximately 100 square feet with 3 inches of material. One hundred square feet may sound like a lot of space, but that is only a 10' by 10' area.

A mature tree's roots can fill many times that area. First spread the organic matter over the area to be amended and work it into the top 6 inches of the soil. Next spread the sand over the clay/organic matter layer and mix it in. A tiller works well for this task. If you don't own one, they can be rented. Check the pH and texture of any amended soil on a regular basis to see how it is changing. The organic matter will decay and seem to disappear. Since clay soils tend to be naturally alkaline and the decaying organic matter will slowly acidify, it will be important to have the pH tested to check its continued suitability for the plants you are growing.