How to Fix Clay Soil*


Hello, my backyard is full of clay soil, how can I fix it? I was thinking of mixing compost and fine sand into the soil to improve the soil condition and drainage.



Thank you for contacting Toronto Master Gardeners.

Clay can be a frustrating soil to deal with. Over the years many people have tried many different approaches.

Before attempting to improve clay it is important to understand how it differs from other soils. When you have a hand full of regular garden soil you can see how the particles are loosely fit together with spaces for air and water to collect. In clay the particles are a different shape. They are more like flat disks or flakes. When the particles line up the discs of clay fit more snuggly together so there is little or no space for air pockets or space for water to pass through. The more one manipulates the clay the more packed these discs become and what little air and drainage space there was collapses. If one adds sand to the clay particles, together they essentially form cement as the sand fills in whatever air spaces.

There are factors which can further compact the clay. When it rains the pounding of the rain drops and pooling of water will further compact the clay. Traffic from people and machinery and working the soil while it is wet  also further increases the compaction of the soil.

Current literature talks about slowly incorporating compost into clay soils. Mixing the compost into the top few inches can allow the clay to slowly loosen up. You will need to do this repeatedly over a few years to slowly make a difference. Frost will also help break up clay clumps. Putting a few inches  of wood chips over the top of the soil will deflect rain and stop pooling on the surface. If you can start some plants growing in the area, their roots will slowly work into the clay and  start breaking up the clay particles. Creating this environment will encourage insects and worms to enter the habitat. They will in turn also work loosening up the clay. There is no one magic answer to returning clay to fertile soil but creating the right environment will over time.

You may also wish to have the soil/clay tested. This will give you information on what nutrients are in your soil and may give a clearer idea of how to proceed. You can find labs for testing soil at: Soil Testing Labs

Improving soil takes time, clay can not be fixed quickly. If you would like a quicker solution for creating a garden you will need to use raised garden beds. Depending on how high you raise the bed you will have a layer of soil you could plant directly into. The roots from your plants would gradually work their way down and ultimately help break up the clay underneath. The following site is a good start for looking at different styles of raised beds.

Raised Bed Gardens

Good luck. With careful planning and patience I am sure you can have a beautiful yard.