Artificial turf over grass or dirt: why the lawn comes out first, and where the sod goes

01What happens if turf goes straight over grass?

Three things go wrong:

• It sinks as the grass breaks down. CSU Extension notes that killing a lawn with herbicide “leaves the organic content (dead grass and roots) in place to decompose” (CSU Extension). Under turf, that layer shrinks unevenly and the turf sinks with it. The Synthetic Turf Council’s base guidelines, written for sports fields, call organic soils “unstable” and “sensitive to water,” and start every base by digging them out (STC, 2017).
• The grass comes back. The same CSU guide warns that scalping a lawn and burying it under compost and 8 to 12 inches of wood chips “still may not kill all of the bluegrass.” Turf backing is far thinner than that, and it is made to let water through.
• Water has nowhere to go. Water passes through the backing onto a mat of thatch and roots, not a draining base. Why turf puddles is in what happens to artificial turf when it rains.

Killing the lawn first doesn’t help: spraying, solarizing or smothering it leaves the dead sod in place, and that is the layer that has to come out.

Manufacturers say the same. FieldTurf’s installation guide says to “remove grass, sod, roots, mulch, and rocks” with a sod cutter, shovel and pickaxe, and that artificial grass “should not simply be placed over untreated soil” (FieldTurf Landscape).

In Firestone it is also the rule. The town’s development code says “Artificial turf shall not be installed over existing grass or compacted dirt” (Firestone Development Code 16.6.4), and that section covers single-family lots that were built before the code, not just new ones (16.6.1). This is general information, not legal advice. The rest of Firestone’s standard is in what a turf spec sheet should say, and other towns’ rules are in our guide to artificial turf rules in Northern Colorado.

02Can turf go on bare dirt, pea gravel or an old rock bed?

Not as they are:

Bare dirt. Across much of Northern Colorado, the dirt is clay. The Colorado Geological Survey says expansive clays “can expand up to 20% by volume when exposed to water” (CGS), and Longmont tells residents its clay soils take water in slowly (City of Longmont). Turf laid straight on that sits on mud after every storm and moves when the clay does. Firestone’s rule names compacted dirt for a reason: packed soil isn’t a base, however hard it feels in August. Digging also wakes the weed seeds in it; CSU says disturbing soil “brings weed seeds to the surface where the warmth and moisture germinate them.” What clay changes about the job is in artificial turf on clay soil, and a yard that is already a mud pit is in will turf fix a muddy backyard.

Pea gravel. It drains, but it won’t hold still. The Federal Highway Administration’s gravel-roads guide explains why: crushed stone “will interlock better” with the stone around it, while “natural stone with a rounded shape will tend to shift and move under loads more easily” (FHWA, 2015). Under turf, that means footprints, ruts and soft spots where people and dogs walk most. Converting a dog run? See pea gravel or turf for a dog run.

Old rock beds. A river-rock or cobble bed is usually uneven stone on landscape fabric, with years of dirt and weeds between the stones. Stone that size can’t be leveled into a base, and winter works on it. The Synthetic Turf Council notes that “Freeze-thaw cycles typically cause rocks to migrate towards the surface,” and that big rocks “can present a threat to the base’s integrity over time.” Northern Colorado has plenty of freezing nights: the NOAA stations at Fort Collins and Longmont average 150 and 177.7 days a year with a low at or below 32°F (1991–2020 normals).

A new build’s dirt backyard has its own questions: see turf in a new-build backyard.

03How does the old lawn come out?

One of three ways, depending on the yard:

• Sod cutter. A walk-behind machine that slices under the grass so it lifts off in strips. CSU calls it quick but notes it “requires heavy equipment” and leaves “the dilemma of how to get rid of the rolls of sod.”
• Excavator or skid steer. Takes sod and soil out together, down to the depth the base needs. A narrow gate or a slope changes the plan.
• Shovel and pickaxe. For small areas, tight side yards and the edges along beds and walks.

Whatever the tool, don’t rototill the lawn under. CSU warns that tilling “can propagate weeds like bindweed and Canada thistle.”

Before anyone digs, Colorado 811 says that regardless of a project’s size “you are legally required to contact Colorado 811 at least three business days before you dig,” and to dig by hand within 18 inches of a utility mark (Colorado 811). This is general information, not legal advice. Colorado 811 marks public utility lines only, so your sprinkler pipes are yours to find; what happens to them is in your sprinkler system after artificial turf.

04What about bindweed in the old lawn?

Plan for it before the base goes in, because it will outlast the digging. CSU’s PlantTalk says field bindweed roots “grow deeply, 20 feet or more, as well as laterally,” that a root “is capable of growing into new plants,” and that its seeds “can survive for 20 years” (PlantTalk 2104). No sod cutter or excavator reaches 20 feet. Shade works against it, since CSU calls bindweed a sun-loving plant that cloth can help shade out, but a vine that survives will find seams, edges and drainage holes. Keeping them out after the install is in weeds growing through artificial turf.

05Where do the cut sod and dirt go in Northern Colorado?

Not into Larimer County’s green-waste pile. The county’s Green Waste Program will not accept “root balls, soil” among other things, and “all mixed loads will go to the landfill” (Larimer County). Cut sod carries its roots and a layer of soil with it. Where it can go:

Two options skip the hauling. CSU says a healthy lawn can be cut into strips, rolled up and given away, or flipped over to decompose in place under compost and mulch. That second one works in a bed you’re planting, never under the turf.

Old artificial turf is a different job; see how to dispose of artificial turf.

06What should a quote say about the old lawn?

Ask before you sign. A good answer is specific:

1. What comes out? All sod, thatch and roots, plus any loose rock, gravel and old fabric, with the dig depth tied to the base your soil needs. A weak answer lays fabric or base over the grass.
2. How does it come out? The tool, and its route through gates and over walks.
3. What about bindweed? Treating it before the base goes in, and a plan for shoots that appear later.
4. Where does the sod go, and is hauling it in the price? Several sites above charge by the cubic yard.
5. Who calls 811, and who finds the sprinkler lines?
6. In Firestone: does the plan keep turf off existing grass and compacted dirt?

More are in what to ask a turf installer and DIY or professional; afterward, see checking the base was installed. Our artificial turf installation page walks through a lawn replacement.