How Deep is Your Soil?

Dana Nichols

The answer to this question should guide your garden design and irrigation habits. To find out how deep your soil is, just grab a screwdriver and start poking around. Verify your findings by lining up the screwdriver to a ruler.

For shallow soils (less than 4 inches), the general rule is to minimize grass, which does best in medium to deep soils (greater that 8 inches). If you do have shallow soils, choose plants that can thrive there such as four-nerve daisy, Blackfoot daisy, pink skull cap, esperanza, mountain laurels and more. Hand-watering and/or drip irrigation is all that’s needed to maintain these plants.

With medium depth soils (8 inches to 12 inches), you have more options as far as turf grass is concerned. Still, try to limit the amount of turf you use. We never recommend using it as a default ground cover, but rather as a functional part of the landscape. If possible, plan for only as much grass as people or pets will use. As for irrigation, water deeper and less frequently. Also, top dress annually with compost to improve what you have.

Deep soil (greater that 12 inches) offers you the most options when it comes to turf. Grass planted in deep soil needs little supplemental water to survive. But in San Antonio, deep soil usually means clay soil. Build on what you have by aerating and top dressing with compost at least every two years.

Many locations with deep soil also have large shade trees such as oaks. If you’re lucky enough to have oaks or other trees in your yard, limit the grass underneath them. For the healthiest trees, remove or limit grass out to the tree drip line. Instead, apply mulch and natural leaf litter. There’s a reason you don’t see trees on the grasslands or grass in a forest: they prefer to live separate lives, if possible. Here in South Texas, I’d rather have the shade from trees.

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