Can You Lay Turf Over Existing Grass? What Happens and How to Do It Right

Short answer: you can physically unroll turf on top of an existing lawn, but it rarely roots properly and no turf grower or university extension service recommends it. The new sod has to push roots through a mat of grass and thatch before it reaches soil, so it dries out, lifts at the seams and dies in patches while the old grass and weeds grow up through it. University of Florida IFAS Extension puts it plainly: “Do not put sod over existing weeds and grass.” The right way is to kill or strip the old grass, loosen and level the soil, lay the sod tightly on moist, firm ground, roll it, and water daily for about two weeks. Done like that, most sod is rooted in 10 to 21 days. In the UK and Australia the product is called turf; in the US and Canada it is sod. The method is the same.

What actually happens when turf goes over grass

Sod is a thin slab of grass with roughly 1/2 to 3/4 inch (1.3 to 2 cm) of roots and soil attached, according to University of Maryland Extension. That sliver holds very little water, and the sod survives only if new roots grow down into the ground beneath within two or three weeks. Put a lawn in between and five things go wrong at once.

• No soil contact. Roots hit grass blades, stems and thatch instead of soil. Old lawns often carry a spongy thatch layer that roots must cross before they find anything to anchor in.
• Air pockets. A springy, uneven surface leaves gaps under the sod. UF/IFAS tells you to tamp or roll “to remove air pockets and ensure good soil contact”; you cannot roll out a gap that is filled with live grass.
• The old grass and weeds grow through. Sod shades the lawn beneath it but does not kill it. Bermudagrass, couch grass, dandelions and bindweed come up through the seams within weeks, and a different species underneath gives you a patchwork.
• A drainage break. The buried grass and thatch rot into a dense organic band between two soil layers. Water perches on it in wet weather, and in hot weather the sod above dries fast because its roots never went deep.
• Height mismatch. The surface ends up 1 to 2 inches (2.5 to 5 cm) higher, proud of paths, patios and drive edges, so the mower scalps the edges and water runs off onto hard surfaces.

The usual result is sod that looks fine for a week, browns along every seam, and is riddled with the old lawn by the second month.

What sod needs, according to extension guides

• Bare, prepared soil. Mississippi State University Extension states that “sod establishes best over bare ground” and says to kill existing vegetation with a nonselective herbicide such as glyphosate, then till it under. Rutgers NJAES says to “strip the old grass and thatch layer to bare soil, or destroy it with herbicide and a rototiller.” The UK grower Rolawn is equally direct: “Turf should always be laid onto properly prepared soil, not over existing grass.”
• A firm, level bed. Purdue Extension describes soil “firm enough to walk on with the top 0.5 inch of soil loosened.” Michigan State’s sod bulletin gives the same test: a person walking on it should sink no more than 1/2 inch (1.3 cm).
• Moist, not wet. Clemson Cooperative Extension says to dampen the soil just before laying so roots are not set on hot, dry ground. Colorado State University suggests moistening the soil 6 to 8 inches (15 to 20 cm) deep several days before the sod arrives, so it is slightly moist but not so wet it compacts underfoot.
• Time to root. Purdue says most grasses are “fairly well rooted within 10 to 14 days if temperatures are optimal”; Maryland and Colorado State give 2 to 3 weeks. In that window the sod must never dry out.

Your options compared

A lawn that is thin rather than dead is usually a renovation job, not a replacement job; see our guide on whether to kill weeds before overseeding before you order a pallet of sod.

The minimum acceptable shortcut: scalp, kill, top-dress

If you cannot hire a sod cutter or rotavator, this is the least you can do and still expect the sod to take. It raises the lawn level slightly and is not as reliable as full preparation.

1. Spray the area with a glyphosate product at the label rate while the grass is growing. Wait until it has yellowed, usually 7 to 10 days, and respray anything still green; UF/IFAS notes that “several applications may be needed.”
2. Mow the dead lawn as low as the mower goes and bag the clippings. Rake hard, or run a scarifier or power rake, to pull out as much dead grass and thatch as possible.
3. Spread 1 to 2 inches (2.5 to 5 cm) of screened topsoil or a topsoil and compost mix, rake it level, fill low spots, and tread or lightly roll it firm.
4. Water it, wait a day, then lay and care for the sod exactly as below.

Skip the shortcut where the old lawn has more than about 1/2 inch (1.3 cm) of spongy thatch or the soil beneath is compacted: the dead layer will hold water in winter and the new roots will still stop at the hard pan. Our guide to preparing hard, compacted soil explains how to tell.

How to lay sod properly, step by step

1. Remove the old lawn

Kill it with glyphosate and till the dead material in, or cut it out with a rented sod cutter set to about 1 to 1.5 inches (2.5 to 4 cm) and haul the strips away. Killing first is more reliable against bermudagrass, couch grass and other spreading perennials. Both are covered in how to remove old sod.

2. Loosen, amend and grade

Till or dig at least 4 to 6 inches (10 to 15 cm); Mississippi State works the top 6 to 10 inches, and the Royal Horticultural Society recommends 20 to 25 cm (8 to 10 in) to remove compaction. Mix in compost; Colorado State suggests 3 to 5 cubic yards of organic matter per 1,000 square feet. Rake to a grade that falls away from the house, about 1 foot in 50 feet (2 percent) by Purdue’s rule of thumb, and set the finished soil about 1 inch (2.5 cm) below paths and edging so the sod ends up flush.

3. Fertilize, firm and moisten

Rake in a starter fertilizer: Purdue suggests 0.5 to 1.0 lb of nitrogen per 1,000 sq ft, Michigan State 10 lb of 10-10-10 per 1,000 sq ft, Rutgers 30 to 40 lb of 5-10-10 per 1,000 sq ft, and the RHS about 35 g per square metre of a general fertiliser. Firm the bed by treading it in two directions or with a light water-filled roller (200 to 300 lb), rake out the footprints, and water so the top few inches are moist the day before delivery.

4. Lay it the day it arrives

The RHS says to lay turf within 24 hours of delivery; in hot weather, the same day. Start along the longest straight edge and work across. Stagger the joints like bricks in a wall, push the pieces tightly together without stretching or overlapping, and on a slope lay across it, starting at the bottom. Michigan State advises against small pieces along the outside edges, which dry first; put offcuts in the middle. Work from boards.

5. Roll, then water within 30 minutes

Roll or tamp lightly, perpendicular to the direction you laid, to press the roots onto the soil. Rutgers and Michigan State both say to start watering within 30 minutes; Clemson says to wet the soil to 4 inches (10 cm) on that first pass. The RHS also suggests brushing a sand and soil mix into the joints so the edges do not dry.

6. The first two weeks

Michigan State’s instruction is to water at least once a day for the first two weeks; Purdue says every morning until rooted, about 10 days. In summer heat, Mississippi State notes, more than one watering a day may be needed in week one. The soil under the sod should be soft underfoot but never oozing, and no corner should curl or turn grey-green. After week two, water every other day, then move to a normal deep schedule of about 1 inch (2.5 cm) a week once the sod resists a firm tug. Keep traffic off until then.

7. First mow

Mow only once the sod cannot be lifted by hand, usually 2 to 3 weeks, or 7 to 14 days in warm growing weather. Rutgers says to cut once the grass reaches 3 to 4 inches (7.5 to 10 cm) and never closer than 2 inches; Michigan State says mow at 3 to 3.5 inches when blades pass 4 inches. Use a sharp blade, let the surface dry first so the mower does not tear the sod, and feed again 4 to 6 weeks after laying.

When sod is worth it and when seed is better

Sod costs several times more per square foot than seed, but Maryland Extension lists what you get for it: an instant lawn, faster establishment and a longer installation window. It also holds slopes immediately and sidesteps the birds, washouts and weed flushes that make seeding a gamble. Seed wins for large areas on a budget, for mixing species to suit sun and shade, and for cool-season lawns sown in late summer, which is also the best sodding window. Purdue calls fall the optimum time for cool-season sod and Maryland gives September to November; the RHS recommends mid-autumn to early spring in the UK, whenever the soil is neither waterlogged nor frozen, and warns against mid-spring to early autumn laying because of the watering burden. Warm-season grasses such as bermuda, zoysia, St. Augustine and buffalo are best sodded in late spring and early summer. If you go the seed route, start with preparing soil for grass seed.

Coverage, quantities and terminology

• US and Canada: sod is sold by the pallet, which Mississippi State says typically covers 450 to 500 square feet (42 to 46 square metres). Measure, add 5 to 10 percent for cutting waste, and order whole pallets.
• UK, Ireland and Australia: turf is sold by the roll, most commonly 1 square metre each. Rolawn recommends a topsoil depth of 100 mm minimum, 150 mm preferred.
• Words: in the UK “turf” is the rolled product; in US turfgrass science “turf” is any mown grass surface and “sod” is the product. “Instant lawn” is the Australian retail term.

Related guides: How to Transplant Grass: Moving Sod and Plugs Without Killing Them

Sources

• University of Florida IFAS Extension – Turfgrass Replacement
• Mississippi State University Extension – Sod Installation and Maintenance
• Rutgers NJAES – FS104: Sodding: Steps to an Instant Lawn
• Purdue Extension – AY-28-W: Establishing a Lawn From Sod
• Michigan State University Extension – E2911: Nine Steps for Establishing a New Lawn Using Sod
• Clemson Cooperative Extension HGIC – Lawn Establishment
• Colorado State University PlantTalk – Installing Sod
• University of Maryland Extension – Sod
• Royal Horticultural Society – How to Lay Turf
• Rolawn – How to Lay Turf