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Amending Clay Garden Soil

The foundation of successful gardening is good soil. I always tell beginning gardeners that if they get the soil right they are two-thirds of the way to a beautiful garden. Unfortunately, few of us move into a home where the soil is already perfect. When I began digging my garden I was faced with a thick layer of highway grade gravel that was left over from when the then vacant lot was used as a community park. In order to remove all the gravel it was necessary to take with it most of the arable topsoil. That left me with a heavy, clay-based subsoil that was harder than a terra cotta pot.

Few things can strike fear into the hearts of gardeners like heavy clay soil. It is almost impossible to grow anything in the stuff. It is gooey when it is wet, and brick hard in the summer.

Why is Clay Soil So Troublesome?

The problem is that clay particles are very small in comparison to others found in the soil. For instance, if a clay particle were the size of a baseball, the average grain of sand would be, relatively speaking, the size of a Greyhound bus. Because clay particles are so tiny they pack together easily and become very dense, virtually impermeable to water and air, which are essential for healthy soil.

Use Humus to Improve Clay Soil

Now if you have clay soil, there is no reason to call in a backhoe or a D-9 dozer to dig it out. A better idea is to simply amend it. This will help break up the clay particles so water can trickle through and delicate roots can grow in the air pockets. The best way to separate these particles is to integrate coarser or larger particles such as humus. Humus is any decayed organic material like leaf mold, old ground up pine bark or compost. If you do not have a compost bin you can purchase bagged soil conditioner or even have it delivered by the cubic yard.

Get to Digging

Begin by loosening the clay in the area where you want to create a bed. Dig down about 12 inches. Once the ground is broken up add 3 inches of bagged garden soil, 3 inches of compost and 3 inches of ground, decomposed pine bark.

At the Garden Home we used Pro-Mix as our bagged soil amendment. It contains a biological growth enhancer called Mycorise®, which is a naturally occurring fungus that helps plant roots take in water and nutrients. The plant in turn provides carbohydrates for the fungi. Gardeners benefit from this symbiotic relationship by enjoying the vigorous plant growth it produces. If you push back the top layer of soil in your flower beds and see those white stripes then you've hit pay-dirt.

Once you have added all the amendments, till the ground until everything is well-blended. If you do not have access to a tiller you can do this by hand with a garden fork or shovel. It just takes more effort.

You will know that you have the texture right if you can squeeze a moist handful of soil in your fist and it easily falls apart when you open your hand.

Add Manure to Your Soil

Now to further improve your soil, add some well rotted manure. Not only does it help the composition of the soil but it brings nutrients as well. When you purchase a bag of basic commercial fertilizer like 13-13-13 you get 13% nitrogen, 13% phosphorous and 13% potassium but nothing else.

Granted these are staples that plants need, but they also need other trace elements such iron, boron, and magnesium. Manure has all these trace elements plus a heaping dose of nitrogen, phosphorous and potassium. For plants, manure is like a well-balanced meal and a multi-vitamin all in one.

I recommend purchasing manure in bags from your local garden center. Typically bagged manure has gone through a heat process that sterilizes any weed seeds that might be lurking in there and it helps to deodorize it. Also, you do not have to worry about it being too fresh and burning your plants. Check the back of the bag for recommend rates of application.

Once you have the texture just right and have added the manure, top the soil with 2 to 3 inches of wood mulch. I prefer pine bark chips, but any wood mulch will do. As the wood decomposes it will supply your garden with plenty of organic matter plus reduce weeds and retain moisture.

Good to Know:

Sandy soils can be amended too. Simply till in 2 to 3 inches of humus such as manure or compost to help bind the soil. This will improve water retention as well as add nutrients.