We received a great question last week from Terry who said, “I have a huge pile of sand and a huge pile of clay-based dirt that I am going to put in my garden to raise it up for better drainage. Should I put a layer of sand down 1st and then a layer of dirt or dirt 1st and then sand or should I just mix them together?”
Many articles, books, and “experts” still recommend this practice of adding sand to clay soils and its a question we still get pretty frequently. On the surface the practice makes sense but the answer might surprise you!
Contrary to popular belief, research (University of California Agricultural Extension & the U.S. Department of Agriculture) leads us to believe adding sand to clay soil, can actually be detrimental! Remarkably, a mixture of sand to clay actually tends to pack more densely than heavy clay soil, creating an easily compactable soil that isn’t fun to garden in. (If you add a little of water you can even make your own bricks)
Adding soil amendments with organic material, such as finished compost, is my favorite method to improve both infiltration and soil structure in the heavy clay alkaline soils we typically see here in North Central Texas.
You might also consider amending with (and incorporating) expanded shale, but although it is a great product, it tends to be a little cost prohibitive on a larger scale.
Topdressing yearly with ½’ -1” of a good quality compost is a great method to improve your soil over time. Others have had success adding up to 2” + of compost and incorporating into the top 6” by double digging or even a one-time minimum tillage (over-tilling can open a whole new can of worms).
Another great soil improving practice is to maintain 2”-4” of mulch in your planted beds. Not only does mulch reduce weed pressure and maintain soil moisture, as it breaks down, the organic matter improves soil structure over time.
For more information about soil amendments, composting, proper planting, or other AgriLife recommended practices, please visit our new Water University page. http://wateruniversity.tamu.edu
AND For more information on your soil’s texture and nutrient content/ recommendations consider submitting a soil test at http://soiltesting.tamu.edu/files/urbansoil.pdf