Preparing soil to get sod off to a strong start

No matter how beautiful or high performing a sod may be when it’s installed, if the site wasn’t prepared properly, the turfgrass may not live up to its full potential.
Photos courtesy of Graff’s Turf Farms.

Long before the days of television gave us “Extreme Makeover,” sod was pulling off exactly that feat—totally transforming the look of a site in short order. It may be tempting to think that sod is magical; just lay it down, and what once was a mess of dirt and weeds will forever more be a lush bed of green grass. Not so fast. Unless you do the prep work prior to sod installation that perfect looking new turf isn’t likely to last.

“The most important thing is soil amendment; both sand and clay soils must be amended,” explains James Graff, owner of Colorado-based Graff’s Turf Farms (www.graffsturffarms.com). “No matter what kind of turf you’re buying, no matter what is being promised in terms of water savings or wear tolerance or color, the most important thing is to do soil prep. If you don’t do adequate soil prep, it can totally negate any of the features of the turf you’re buying.”

Graff explains that in that region of the country, the Rocky Mountain Sod Growers Association has agreed that a general recommendation of 3 to 4 cubic yards of compost per 1,000 square feet is an acceptable standard for amending soils prior to sod installation.

Part of what impacts how much compost should be incorporated into the soil relates to the prior use of the site. Former farmland that’s been developed might offer soils that are better-than-average quality. Even so, the development process often results in those fertile soils being displaced from the surface, explains Graff. “In new construction, many times when they dig out foundations and footers, they’ll bring a lot of bad soil to the surface, and that’s what gets used to backfill around the building and to form the yard. The result is that we have to try to grow grass—and trees and plants—in soil that’s intended to be 10 feet down. So, it’s really important to bring organics into that soil in order to support any kind of plant life,” he says.

Incorporating composted material is a simple process, but the benefits are far-reaching, says Graff. “You’ll never get a better opportunity to amend your soil than before sod is installed,” he says. “You can aerify a lawn and topdress with compost, and that’s somewhat effective, but there’s no better time than when you have the whole lawn opened up and you can really get the organics down into the soil. It makes a 100 percent difference in the type of performance you’ll see in your lawn and trees and shrubs.”

Graff’s Turf Farms recommends that the soil prep process begin with an initial tilling or “ripping” just to open the soil up. “That just loosens things up so that the ground can be worked,” says Graff. Organic matter (compost) is then put down, followed by another tilling to incorporate it. The second tilling also creates a finer material, which can be graded more easily and precisely before sod is installed.

“Till as deep as you can till,” advises Graff. “Bluegrass in this region roots in 4 to 6 inches deep. Tilling deeper than that is great; tilling shallower than that just robs the turfgrass of a chance to root in deep and save water and recover better.” If the ground is so hard and rocky that these depths cannot be achieved, he emphasizes the message that “doing something is better than doing nothing.” Coming up short of the guidelines set by your sod supplier doesn’t mean the turf is all going to die, it just means the turf might not perform at 100 percent of its potential or may take longer to fully establish or may require more water, he explains.

The key step is to incorporate quality organic material, which lasts several years in the soil, keeping that soil looser and draining better while at the same time boosting fertility for plants. “People get hung up on what kind of compost is best to use,” says Graff. “I used to be adamant that it had to be cattle or dairy-based compost. Now I’m just adamant that you should use some type of compost; any kind of organic is better than nothing.” Different regions of the country tend to have different forms of compost that work best in that region, he adds. Regardless of the origins of the compost, the manure must be fully “matured” and mixed in order to avoid damaging the roots of the sod. “You have to be careful to stay away from something that hasn’t been properly dried and composted,” says Graff. “It can be too ‘hot,’ or the pH could be wrong, or the salts could be too high.”

After an initial tilling to open the ground up, properly composted organic matter should be applied and then incorporated into the soil.

Graff advises purchasing compost only from reputable sellers, and asking to see spec sheets on the material to see the age, pH, source and other factors related to the compost. Some sellers try to speed the process along and the result is a compost that is too high in nitrates. “If that’s the case, your lawn will burn just like if it didn’t have enough water,” he explains. “There’s just nothing more disheartening than seeing beautiful turf go down on hot compost because budgets were tight and somebody got a good deal on it—you know what’s going to happen.”

Graff says you should be able to pick up compost in your hand and smell it “without losing your lunch.” It shouldn’t be so fresh that you’re afraid to touch it, and it should have a musty smell, but not stink. The pile shouldn’t steam when you stick your shovel in it. He also recommends looking for compost material that has the consistency of coffee grounds: fine and loose rather than a material that you can squeeze and pack firmly in your hand.

Sod farms will sometimes handle sod installation, but Graff says that anyone, from homeowners to lawn care contractors, can do the work themselves. On many projects he sees, Graff says, “There’s a lot of shortcuts being taken.” Sometimes, through no fault of the landscape contractor, budgets set for the job don’t allow for proper deep tilling, or the site physically is unable to be tilled to a proper depth or an inexpensive compost is specified.

Matching the soil type on the site to the soil type of the sod is also important in some cases. “It’s crucial in a sports turf setting, where drainage and safe playing surfaces are critical,” says Graff. “When it comes to commercial or residential installations, the match is only important in one way: it’s harder to get clay-based turf to interface with sandier soil, but a sand-based turf will interface with sand or clay soil. And, if you’re going to have clay on clay, you just don’t have a great soil to work with anyhow.”

Prep Work

Turfgrass Producers International (www.turfgrasssod.org) recommends the following steps in order to properly prepare a site for installation of sod. Your turfgrass supplier or local extension agent may recommend modifications or additions to these instructions.

  1. Clear the site of all building materials (wood, cement, bricks, etc.), as well as any buried stumps, rocks, stones or other debris that is larger than 4 to 5 cm (2 to 3 inches) in diameter.
  2. Rough grade the entire area to eliminate any drainage problems on the property. This would include sloping the grade away from building foundations, eliminating or reducing severe slopes and filling low-lying areas.
  3. Initial tilling, to a depth of at least 5 cm (2 inches), should be completed prior to adding any topsoil or soil amendments. This will control most annual weeds, alleviate subsoil compaction and permit a bonding of the topsoil to the subsoil, and improve root penetration and water movement.
  4. Add topsoil to achieve a total topsoil depth of 10 to 15 cm (4 to 6 inches), after firming. The topsoil should be a loamy sand, sandy loam, clay loam, loam, silt loam, sandy clay loam or other soil suitable for the area. To the extent possible, practical, affordable and available, incorporate humus (fully decomposed organic matter) into the topsoil.
  5. Test the soil pH with a chemical soil test to determine if any pH correction materials are required. Acidic soils (pH of 6 and below) can be improved with the addition of lime. Alkaline soils (pH of 7.5 and higher) can be improved with the addition of sulfur or gypsum.
  6. Apply “starter fertilizer” that is high in phosphate (P, or the middle number on a bag of fertilizer), at a rate recommended for the particular product. To prevent root injury to newly installed turfgrass sod, this fertilizer should be worked into the top 7 to 10 cm (3 to 4 inches).
  7. Roll the area with a lawn roller to firm and settle the surface and reveal any low spots that should be filled to match the surrounding grade surface.

Source: Turfgrass Producers International

Patrick White is a freelance writer and editor who has covered every aspect of the green industry in the past 13 years. He is based in Middlesex, Vt., and is always on the lookout for unusual stories.