Clay soil can be frustrating. It doesn’t drain in the spring and cracks like the Grand Canyon in the summer. Red clay soil makes it difficult for many southern and northwest coast farmers to produce a good crop. If you have it, you're probably wondering how to improve clay soil.
Most likely, when you bought your property, it didn't come with perfect soil. I understand – my Kentucky soil has been challenging. I keep wishing for a soil Fairy Godmother to wave her magic wand and give me the ground I want.
Clay soil, called ultisol by soil scientists, has an average of 16% air space, 2% organic matter, and 82% minerals. What gardeners typically strive for is 50% air space, 5 % organic material, and 45% mineral content. Big difference, right?
Until we find a soil fairy godmother, your job is to take the soil you were given and make it better. With a little work, I have nurtured multiple productive garden areas, and I can physically see and feel the difference in my soil. You can improve your soil too by following a few basic principles – and a little elbow grease.
Two Simple Ways To Test For Clay
First things first: you need to be sure you have it before you start learning how to fix clay soil. If you aren't sure, you can find out if you have clay soil by doing a texture ribbon test or a jar test.
To do the ribbon or feel test, take a handful of soil from about 3 inches under the ground's surface.
Spread the soil in a pan or on a plate. Pick out any rocks or other debris. Next, put your soil in a pile and add a small amount of water so that it is the consistency of putty. In other words, moist but not wet.
Roll the soil into a ball in your hand. If it doesn't form a ball, then you have sandy soil. If it forms a ball, the next step is to form it into a strip or ribbon between your thumb and forefinger. You may have done this once upon a time with Play-Doh.
While making a ribbon, if the soil crumbles, then you have loamy sand. If the soil stays intact and makes a ribbon 2-3 inches long, you have clay.
The Jar Test
For the jar test, you will need a glass jar. A pint-sized Mason jar or an old spaghetti sauce jar works well.
Collect about one cup of soil from about three inches deep. Remove any pebbles or rocks from the sample. Add the soil to the jar. Next, fill the jar with water about one inch from the top. You can add a teaspoon of borax to help settle the particulates. If you don’t have borax, use dishwashing detergent or leave this step out.
Place the lid on the jar. Shake it vigorously for several minutes. You want it to mix well. Set the container on a level surface and leave it alone for 24 hours. After that time, the soil will separate into layers. Sand is heaviest and sinks to the bottom. The middle layer is loam, and the clay is at the top. You should end up with clear water at the top.
Which layer is the thickest in your jar? If it's the clay layer – you guessed – you have clay soil.
The Good News About Clay
There is good news about that heavy wet soil. Clay soils tend to be more fertile than other soils such as sand. The clay pulls together in positive ions. This means it is more likely to hold nutrients.
In summer, clay holds in the moisture, and plants don't dry out as fast as they do in sandy soil.
The Bad News About Clay Soil
Clay soil may have an overly low (acidic) or high (alkaline) pH value, which makes it hard for nutrients to be absorbed. Taking a soil test is the best way to find out the pH of your soil.
Ideally, you want your soil to be in the range of 6.3 to 6.7. If your soil is not in the range, then you can start adding things to help adjust it. Soil pH does not change overnight, but working towards that goal is always good.
Clay soil holds moisture. This can be great in August but detrimental during spring planting. Clay soil tends to harbor moisture diseases such as root rot and verticillium wilt.
Furthermore, wet soils will leach out nitrogen so that it is not available for your plants.
Compost, Compost, Compost
Wanting to know the secret for how to improve clay soil? The biggest and the best thing you can do is to till in lots of aged compost. If you are starting fresh, then you can not add enough compost. Till it into the soil when the soil is dry. You don’t want to till clay soil when it is wet.
The most important thing that compost does is lighten the soil. This allows the soil to drain better and allows air circulation to get among the roots. This, in turn, makes it more friendly to earthworms and beneficial bacteria.
Good air circulation also helps to keep down disease.
You can keep adding to your soil's complexity by mulching with natural materials. In a garden with clay soil straw, shredded leaves and grass clippings are your friends. These will continually break down and add more organic matter to the soil.
In addition, mulch will help feed your soil microbes. This will make your soil healthier and more active, getting the desired nutrients into your plants.
Avoid wood or pine mulches in clay soil. Typically clay soils are on the acidic side. These mulches may lower the pH and not give you the positive balance you need.
End of Year Cleanup
It's important to put your garden to bed each year. This is an essential element for how to improve clay soil.
At the end of the season, clean up all plant residue and take it to the compost. Next, spread a thick layer of compost in the garden. In the fall, in areas where you won't have a crop till spring, you can also spread fresh manure.
Lastly, add a layer of mulch such as straw or mulched grass clippings. This will protect the compost, allowing the earthworms and insects to pull it into the soil. It will also prevent nutrients from washing away during winter rain or snow.
Plant A Cover Crop
Planting a cover crop in fall will also add nutrients and protect the soil. Cover crops such as rye, winter wheat, and buckwheat are all ideal for fall planting. You can also plant spring cover crops in a section of your garden.
I like to have cover crops in my rotation. That way, I get the soil improvement and in some cases, another crop to eat.
When your cover crop is done growing, you simply dig or till it into the soil. The decaying plants will add nutrients and texture.
Pathways Are Your Friend
Clay soil has problems with compaction. If you're wanting to figure out how to improve clay soil, know that walking on your soil makes compaction worse. You should always have pathways that are areas for people's feet so that the rest of the soil can breathe.
When clay soil becomes compacted, it also becomes hard and develops a rock-like consistency. Plants cannot grow in soil like that.
Never walk on your beds. An exception maybe if you are doing a whole garden tilling. However, after you till put some designated pathways in place, so feet, wagons, and wheelbarrows don’t mush the soil down.
Tilling Clay Soil
Tilling clay soil needs to be done with care. Clay soil naturally benefits from no-till or low till techniques.
Clay soil easily compacts, as we have said. Tilling at the wrong time can actually make the soil more compacted and bad for your plant's roots.
Never try to till clay soil when it is wet. The soil will clump together, and even after it dries will remain hard and stuck together.
Need Good Soil Now?
So you have heavy clay soil, but you need to know how to improve clay soil so you can grow some veggies. Build raised beds. By using some old dimensional lumber, you can get your soil off the ground and build it the way that meets your plant's needs.
Raised beds help with water drainage and make it easy to add soil amendments that benefit your plants. Make sure your raised bed is narrow enough in width that you can reach into it comfortably. You don’t want to walk on your raised bed.
I can tell you that having a raised bed will work on the soil below as well. When I had some leftover lumber, after building a barn, I built some raised beds out of the 2×10 white pine. I filled them with compost, garden soil, and some starter soil and added compost every fall.
Eventually, the lumber broke down and needed to be replaced. In the process, I discovered that the original hard clay soil underneath was beautiful. It had a great texture and was a nice dark brown color. The earthworms and certainly done their job, bringing all that compost down into the soil.
Soil improvement takes time, but if you follow my advice, you'll start to see positive changes in the first season. Every season after that, your garden will continue to improve.
Not many of us are blessed with perfect soil. We have to make do with what we have. But clay soil can be made better – believe me. My gardens are productive because I followed these steps and am always working to improve my soil.