Why North Texas clay is the problem
Most of Dallas-Fort Worth sits on the Blackland Prairie, and the soil under your lawn is a heavy black clay that swells when wet and cracks open in August. When it is dry it is close to concrete. When it is wet it holds water at the surface instead of letting it drain. Neither state is friendly to a piece of sod that has one inch of soil on it and no roots yet.
Sod laid straight on compacted clay does not grow into the ground. It sits on top of it, held down by its own weight, drinking only what lands on the blades. It looks fine for a month. By the second summer it thins out along the seams and dies in the low spots where water pooled. Prep is what stops that, and it is the part of a sod job that homeowners skip most often.
Step 1. Strip or kill the old lawn
Never lay sod over living grass, weeds, or a thick layer of dead thatch. The new roots cannot reach the soil through it. Either rent a sod cutter and peel the old lawn off in strips, or spray a non-selective herbicide, wait ten to fourteen days for everything to die, then rake the dead material off. Cutting is faster and leaves cleaner soil. Spraying is easier on your back.
Rake up rocks, roots, and construction debris while you are at it. Anything bigger than a golf ball comes out.
Step 2. Grade away from the house
Water should leave the house, not gather against it. The usual rule is about six inches of fall over the first ten feet away from the foundation. Walk the yard after a rain and look for where water stood. Those low spots get filled, and any high spot that sends water toward the slab gets cut down.
Keep the finished soil level about an inch below sidewalks, driveways, and patio edges. Sod is roughly an inch thick, so that is what makes it sit flush instead of proud of the concrete, where the mower scalps it.
Step 3. Spread two inches of topsoil
Two inches of a sandy loam topsoil over the graded clay is the single biggest thing you can do for new sod. It gives roots something to grow into right away, it holds water without drowning them, and it keeps the clay from cracking directly under the seams. On a new build with hard fill, go to three inches.
The math: one cubic yard of soil covers about 160 square feet at two inches deep. A 3,000 square foot lawn needs about 19 yards. Our satellite measuring tool works it out from a trace of your lawn.
Do not till the clay deep to mix it in. Wet Blackland clay tilled into clods dries like bricks and you will fight it for years. If you till at all, keep it shallow and only when the ground is dry enough not to smear.
Step 4. Rake and level
Rake the topsoil smooth, fill the low spots you found in step two, and knock down the ridges. Then lightly firm it. A water-filled roller at half weight, or just walking it in, is enough. You want soil that holds a footprint about half an inch deep: firm enough not to sink under the sod, loose enough for roots to push into. Water the bed lightly the day before the pallets land so the sod goes onto moist soil, not dust.
Step 5. Test the sprinklers
Run every zone before delivery day and watch it. Fix the heads that do not pop, straighten the ones that spray the fence, and flag each head so nobody cuts sod over it or drives a pallet jack across it. New sod needs water every day for ten days, and there is no fixing a dead zone after the sod is down without lifting it. If the system is not ready, push the install date.
New builds and fill dirt
Builders finish a lot by spreading whatever was dug for the foundation, then driving equipment over it for six months. The result is fill packed harder than the native clay, often sloped toward the house, sometimes with a layer of gravel and drywall scraps in it. Sod laid on it does exactly what you would expect. On a new build, do the grade check with extra care, rake out the debris, and spread three inches of topsoil rather than two.
What prep costs
When we install, the prep is quoted on the same ticket as the sod, and it is most of the spread in the installed price. A yard that is graded and bare costs less than one where the old turf has to be cut and hauled and topsoil brought in. Tell us what the ground looks like now and we quote it straight. See lawn prep and installation, or read how to lay the sod yourself if you are taking delivery only.
Questions people ask
Do I really need topsoil under sod in DFW?
On most yards, yes. Two inches of topsoil over graded clay gives roots something to grow into and keeps water moving away from the slab. Sod on prepped soil roots in two to three weeks. Sod on bare compacted clay can take a month or more, and some of it never takes.
Can I lay sod over builder fill on a new house?
Not without prep. Builder fill is packed hard by equipment and holds water against the foundation. Two to three inches of topsoil and a grade check away from the house are the difference between sod that roots and sod that sits.
Should I till the clay before sod?
Only lightly, and only if it is dry enough not to smear. Deep tilling wet Blackland clay makes clods that dry like bricks. Grade, top with soil, and rake instead.
Sources
This guide is part of The complete guide to sod in Dallas-Fort Worth.
