Trench Composting Clay Soil: What are the Benefits?

Trench Composting Clay Soil

If you’re dealing with heavy clay soil, you’re always looking for a way to make your ground a little more suitable for growing plants. One option to improve your native soil is trench composting clay soil.

In case you need a refresher, trench composting involves composting organic material in place. You dig a trench, pile in items like food waste and leaves, and wait. After about six months of anaerobic decomposition, you’re left with a layer of compost a few inches underneath the soil.

When you trench compost clay soil, you boost the soil organic matter, leading to numerous benefits.

Short Answer: Trench Composting Clay Soil: What are the Benefits?

Trench composting in clay soil increases the organic matter content of the soil. As you’ll read below, organic matter is excellent for improving drainage, increasing nutrient holding capacity, and boosting soil life.

This method of composting also involves a relatively low amount of hands-on labor and little equipment. There’s no turning a compost pile, buying a compost tumbler, or adding finished compost to your plants.

Drawbacks of Trench Composting Clay Soil

As with all composting methods, trench composting has its flaws. Some of the main cons include the need to dig a trench and the potential issues that come with anaerobic decomposition.

When you add in the factor of clay soil, there are a few more drawbacks. 

Clay soils benefit from the incorporation of organic matter, but trench composting forms a layer of compost a few inches underneath the soil surface. This means that you’ll be relying on insects, worms, and plants to mix the compost in with the rest of the soil. While they can do this job, it’s much slower than if you incorporate the compost yourself.

All About Clay Soil

To help learn about trench composting clay soil, let’s explore a bit more about this type of soil.

People use size to separate inorganic soil particles into three main categories: sand, silt, and clay. Sand is the largest, clay is the smallest, and silt is in the middle.

Soils can be any sort of mixture of these particles. You can have a silty clay, a clayey silt, a sandy loam, and much more.

Soils that are high in clay have millions of small particles packed together. Since these particles are tiny, the air spaces between the particles are also small.

To help illustrate the difference between sand and clay soils, imagine you have two large test tubes. You fill one tube with basketballs to represent sand and another with pinpoints to represent clay.

If you pour water into the tubes, the water will flow through the softballs quicker than it will through the marbles. This action illustrates how clay is excellent at holding water but not the best at draining.

These small particles also lead to compaction. However, clay generally has an excellent nutrient holding capacity, which means fewer nutrients leach out. This not only helps your plants, but it also helps limit nutrient pollution of local waterways.

Adding in Organic Matter

Along with inorganic components, soil also includes organic matter. If you obtain a soil test, you’ll often see the percentage of soil organic matter in the results.

Many soils are naturally low in organic matter. But that doesn’t mean it has to stay this way. 

Gardeners often add organic matter to their soils through cover cropping, applying compost, and other means.

Wondering why you should put in the work to increase the organic matter in your soil? Here are a few reasons:

  • Organic matter increases soil nutrient holding capacity.
  • Increased organic matter leads to better tilth, creating better aeration and drainage.
  • Organic matter provides food for microorganisms, leading to a vibrant community of beneficial soil life.
  • Soils are better able to buffer changes in acidity as their organic matter levels increase.

Before you go and add organic matter to the soil, know that different soils benefit from different levels of organic matter. Clay soils require a higher amount than sandy soils to exhibit similar benefits. However, clay soils also hold onto organic matter better than sandy soils.

What is the Best Compost for Clay Soil?

Now that we know why organic matter is so helpful for soils, we have to answer another question. What’s the best way to add organic matter to clay soil?

Compost is a simple way to quickly boost your soil’s organic matter content. When you’re searching for the best compost for clay soil, you want to look for the same things you look for in all compost.

Make sure the compost is free of weed seeds, pesticide residues, and harmful pathogens. It’s also important to add finished compost to your soil. Remember there’s a difference between food scraps and compost!

In terms of methods, one doesn’t reign supreme over another. A compost pile, compost tumbler, and compost trench can all produce compost that will improve your clay soil. The key is to weigh the pros and cons of each method.

While trench composting is a set it and forget it method, it can be difficult to dig a trench in clay soil. If you do select this method, it’s important to note that the finished compost will sit a few inches underneath the soil surface. While plant roots will be able to reach this material, the top inches of soil will still be mainly clay.

If you make compost in an exterior location and then add the compost to the clay soil, you’ll be able to incorporate it into the existing soil. By mixing the compost into the top few inches of soil, you’ll improve seed germination and the growth of small plants.

Final Thoughts

Trench composting can improve the structure of clay soil, but it’s only one of many different composting methods. Other methods allow you to mix compost in with clay particles, creating a uniform soil.

Still, trench composting is a fine way to improve your clay soil, especially on a deeper level.

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