a few inches in most places because it is hard red clay and the torrential rains wash all of the good topsoil away each year. If I put these next to my plants, should I back fill with a less dense soil? Build your garden on top of it. No need to dig at all really. Weed and add compost from your heap. Build it up. The organic kitchen food scraps will break down in your compost bin to form the type of soil you need as a growing medium. If you feel rich, buy a trailer load to get started. The clay is underneath. It could be urban concrete. It does not matter. Never export organic matter from your home. That is where the nutrient comes from. But then, I also have a composting toilet and that prevents a lot of export of organic material. Make your home a one way street for trapping organic material and converting it into the stuff to put on top of your clay. I'm also living on red clay here in Alabama. I've found that grass clippings do wonders for it. I mulch my garden with them. It keeps down the weeds and amends the clay beautifully. Started a new garden spot last year. Left the clippings on all winter. Just had the garden plowed and the soil is several shades further into brown from totally red last year. I have ammended clay soil in Illinois, Wisconsin, Minnesota and recently in Ohio and