Most gardening involves good healthy soil. With container gardens we get a lot more leeway in how we shape and manage or soil, but for in-ground gardens or landscaping we generally have to at least start with what our garden site gives us. In large swaths of the world this means finding ways to work with clay soils. These dense soils can be sticky, difficult to work, and initially deliver limited results. However, they have some surprising advantages and with a little effort at improvement your clay soils can do great things for you, your plants, and your garden. So, let’s roll up our sleeves and dig in to learn more about gardening in clay soils.
What is Clay?
Clay is one of those words we all know but might struggle to define. We know it’s used to make pottery and ceramics, that it’s dense and moldable, and that it is often found in the banks of rivers and the shores of lakes. But what is it really?
Clay is a category of soil type, when soil types are classed by the size of the particles which comprise the soil. The three sizes are sand, silt, and clay in descending order by particle size. Clay soils have a particle size of less than 0.002 millimeters, which makes clay very dense and means that the particles cling together and are shape-able. It also means that water and plant roots have a more difficult time moving through clay soils, which in turn affects how we treat clay soils in our gardens. Clay soils can be rich in nutrients, but they also tend to be poor in oxygen levels and microbial action, making those nutrients difficult to access.
So can we fix our clay soil so that plants can make better use of it? As it turns out, yes we can!
Amending and Improving Clay Soils
There are a number of different approaches to amending clay soils for gardening and landscaping. It’s a bit like making scrambled eggs—everyone has their own technique that works for them and they’re adamant about it! So instead of recommending a particular approach, we’ll outline some basic principles and general options and trust you to explore and learn your own garden space and what it needs.
Adding soil amendments to clay soils can greatly improve them by loosening the soil, adding more organic matter to invigorate soil health, and increasing air flow. For in-ground gardeners and landscapers, a good approach can be spreading 2 to 4 inches/5 to 10 cm of organic matter like compost, leaves and grass clippings, or manure over the area to be improved and then working that organic material into the clay soil to the depth of about 6 inches/15 cm. Some folks advocate doing this a season in advance so that the organic soil amendments have time to biodegrade and improve the soil. If possible we would suggest trying this—soil takes time to change and dense clay soils can need even more time that looser types. When clay soils do loosen and aerate, however, they tend to be rich and fertile, giving great results for both landscaping and vegetable gardening.
A quick note: adding sand to clay soils tend to create something very much like concrete, so sand is not advisable as a soil amendment for clay soils. Some garden guides and old-timer gardeners still give this advice as a method for loosening clay soil, but we don’t recommend it at all.
When planting trees, bushes, and shrubs, it’s generally best to follow the approach we outlined above rather than adding organic matter to the inside of the planting hole. Adding the soil amendment to the planting hole itself can cause problems for the plant’s roots and limit the impact that your amendments have on the soil. Remember, amending clay soils takes time, and it may be a season or two before you see results.
Tilling is a contentious subject in the gardening community. While there may be times for tilling clay soils—putting in a grass lawn, for instance—for gardening and landscaping it’s probably not the best approach. Tilling clay tends to release all of its nutritional potential in one big burst, giving you a potentially great season but then leaving your soil depleted. Local conditions can affect this, however, so it pays to check with your local garden club or extension office and see what they recommend.
Clay soils are not a barrier to gardening—they’re just another natural feature that we need to learn to work with and manage. If you have clay soils in your garden, we hope this helps you get started in improving them and creating the garden space you want. If you have tips, please share them—your advice may benefit another gardener!
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