Understanding your soil gives you a better idea of the plants that will and will not grow in your garden. But, what if you want to grow a plant that requires well-drained soil and you have heavy clay soil? Can you immediately change your soil’s texture in order to successfully grow that plant? Such a drastic change is financially and environmentally unsustainable. Your soil can be improved over time but something that drastic would require you to dig everything out and replace the soil. Clay soil can be improved as can sandy soil. It takes time.
Clay soil is moisture retentive but not friable and bakes hard in the sun. Sandy or silty soil is very porous and does not hold water and nutrients well. Both of these soils can be improved through the addition of organic matter. Every year I added about an inch of compost and top-dressed with two inches of organic mulch to improve the clay soil throughout my garden in Virginia. I spread this across the entire garden, not just around the plants. Organic mulch will decompose and add structure and nutrients to the soil. Rubber and rock mulches do not break down. You should never use rubber mulch, ever. Popular ones are shredded leaves or shredded bark. (NOT THE RED STUFF!) This cover keeps clay soil from baking hard and improves soil structure by increasing aeration in the dense clay. Compost and mulch are also beneficial in sandy gardens because they are rich in nutrients and encourage water retention in the very porous sand. Compost and mulch are often times free! Shredded autumn leaves are a FREE and excellent mulch when applied properly and the average house can generate compost for the garden from scraps of food.
How will the compost and mulch be mixed with the existing soil? Do I need to use a tiller? I don’t recommend using a tiller to work compost into the existing soil. Worms, critters and weather will do this part for you. Actually, I don’t want to till it in because this destroys a lot of beneficial organisms in the soil. There is a complicated network of invertebrates and beneficial fungi below your feet, and it took years to build. One hour of tilling will destroy this. But most importantly, why create more work and hurt your back when you don’t have to?
If you absolutely must have a plant that won’t grow in your existing soil, we all have faced this, you should look at container culture or raised beds. Container gardens allow us to have a wide array of plants with different cultural needs in one space. You will never see agaves growing beside sarracenias in a garden plot but you can grow them in container gardens. A lot of gardeners are faced with rocky or compacted soil or even soil that is fine for other plants but isn’t suitable for the plants that they like. Raised beds allow us to engineer the soil to fit the requirements of specific plants. It is similar to a giant container. Raised beds are popular for herb gardens or cacti gardens because the soil can be well drained.
“If you have clay soil, add sand to improve its texture.”
This is a dangerous myth and will create something similar to cement.
“Just improve the soil in the planting hole.”
Go dig a hole in clay soil and fill it with water. Does it drain away? No, it is like a bowl. This is a dangerous and costly myth. Many plants send out long roots in the top few inches of soil. By only improving the soil around the hole, you are creating a container. When roots hit the sides of a containers they circle or return. This can happen in our gardens because the native soil may be nutrient poor or less aerated. By annually spreading a few inches of compost and other organic mater we can improve the entire garden and encourage roots to spread.
“Clay soil is bad.”
Personally, I prefer gardening in clay soil. If you understand how to properly manage it then you can have a lush garden full of vegetables and flowers. Clay soil holds water so you have to water less often. It bakes hard when exposed to the hot sun but remains cool and moist when there is a layer of mulch on top of it. Knowing when and how much to water is important with clay soils.
Remember that CONTEXT is key in gardening. What may work for your neighbor may not be good for your garden for different reasons. You need to understand your site before you do anything.