Artificial turf around trees: root zones, excavation depth and the ring to leave open

01Does artificial turf kill trees?

Nobody has measured it. CSU Extension says there is no research documenting turf’s effects “to the health of landscape plants with roots growing under the carpet” (PlantTalk Colorado 1537). What CSU has documented is what injures roots, and a careless install can do most of it at once (CSU fact sheet 2.926):

• Soil taken away “can expose and injure roots.”
• Compaction and heavy clay “restrict water and oxygen uptake by roots,” and a turf base is compacted aggregate by design.
• Soil piled on: only 4 to 6 inches over existing roots “drastically reduces” their oxygen and water.
• Water cut off: CSU notes that a lawn and a nearby tree share the rooting area and the sprinkler water (GardenNotes #657). See watering trees after the lawn becomes turf.
• Herbicide under the base: root-absorbed herbicides applied some distance from a tree can still damage or kill it (GardenNotes #656; more in weeds growing through turf).

The damage is slow. CSU says symptoms of construction damage “may appear one to several years after,” so a tree that leafs out next spring hasn’t passed yet. On a new build, the builder’s grading may already have started that clock (turf on a new-build lot).

02Where are a tree’s roots in a Northern Colorado yard?

Near the surface, and well past the canopy. On clayey or compacted soil, CSU puts 90 to 95 percent of a tree’s roots in the top 12 inches and half in the top 4, because the deeper layers are short of oxygen, and says the roots may spread two to five times the canopy’s width. On clay, CSU’s PlantTalk adds, half the roots often grow “along the surface of lawns” (PlantTalk Colorado 1507).

Greeley’s water department says local hard clay sits “sometimes just inches below the surface” (City of Greeley), and our guide to artificial turf on clay soil covers the rest. The layer a turf crew digs out and replaces with base is the layer that holds most of the roots; how deep that goes is in what base goes under artificial turf.

03What do the dig and the base do to those roots?

• Cutting. The Synthetic Turf Council’s base guidelines, written for sports fields, call for stumps and roots to come out of the subgrade (STC). Near a tree, that is the root system. CSU says a tree “may be able to tolerate cuts to one side of its root system, but not all sides” (CSU Tree Preservation During Construction), and turf that surrounds a trunk is a dig on every side.
• Anchoring. Removing surface roots “may harm the tree or make it unstable and prone to falling under windy conditions,” CSU says, and the Colorado Climate Center notes “periodic, severe turbulent winds” near the mountains (Colorado Climate Center).
• Compaction. The base has to be firm to hold turf flat; roots under it get less air and water.

CSU’s construction guide rates species by how they handle losing roots and gaining soil. Among trees common in Northern Colorado yards:

CSU adds that “there is no comprehensive list of species tolerances,” so ask an arborist about your own tree.

04How big should the turf-free ring be?

Measure from the trunk. Three yardsticks, from the least ground to the most:

Windsor’s standard covers development landscape plans, not detached houses (Windsor Municipal Code 15-3-20), but it is a written local benchmark. Read together, CSU’s numbers suggest three zones:

• Inside the root plate: no digging, no base, no turf. Mulch or ground cover only.
• Inside the protected root zone: for a tolerant species, disturb no more than a quarter of it, ideally on one side. For intermediate and sensitive species, leave it undug. CSU adds that clay may need more room still.
• Beyond it: a normal dig, with the crew watching for large roots.

Keep turf off the trunk flare as well. What holds the ring’s edge is in artificial turf edging options, and how much hotter turf runs in sun than in shade is in how hot artificial turf gets.

05Can the turf be built up over the roots instead of dug in?

Over part of the zone, for some trees. Skipping the dig spares roots from cutting, but the base then becomes fill:

• CSU lets compaction- and flood-tolerant species take up to six inches of porous fill and says sensitive species should see no change of grade.
• PlantTalk says roots “should not be covered with soil.”
• Firestone asks for at least 3 inches of compacted base under any turf, and Windsor’s development standard holds cut and fill in the drip line to 4 inches.
• A raised pad changes the grade at its edge, and Firestone bars an install that alters the lot’s drainage pattern; see what happens to turf when it rains.

So a no-dig section might suit a green ash or a cottonwood outside its root plate, on porous aggregate rather than clay, but not an aspen or a sugar maple. Where roots already show at the surface, PlantTalk’s answer is mulch or a shade-tolerant ground cover. That is usually where the turf should stop.

06What do Firestone, Windsor and Fort Collins say about trees and turf?

Not legal advice.

• Firestone requires a town permit before turf goes in, and its turf standard says placement, “particularly under the dripline of trees, shall avoid negative impacts to trees at the time of placement and during the lifespan of the tree” (Firestone Development Code 16.6.4). The code doesn’t define a negative impact. It depends on the tree and the plan; ask Firestone Planning before the dig. See turf in Firestone.
• Windsor exempts detached houses from most of its landscape code but keeps the tree lawn requirement (Windsor Municipal Code 15-3-10). Tree lawns and street trees are the adjacent owner’s job unless an owners’ association or metropolitan district has taken them on, and no tree may be planted or removed in the right-of-way without the Town’s authorization. See turf in Windsor.
• Fort Collins plants shade street trees in the center of the parkway strip. Its Streetscape Standards, adopted in December 2025, bar artificial turf from parkways and other streetscapes for development and renovation applications from January 1, 2026; on local streets a parkway takes turf-type grass or mulched planting beds (Streetscape Standards). Cutting or removing a right-of-way tree takes a free written permit from the City Forester (Fort Collins Municipal Code 27-31). The code doesn’t say whether cutting a street tree’s roots from your side of the sidewalk counts, so ask Fort Collins Forestry first. See turf in Fort Collins.

With design review, draw each tree and its ring on the plan you submit. Our guide to HOA approval lists the rest of the packet, and turf rules in Northern Colorado covers the other towns.

07What should a tree-safe turf plan show?

• Every tree drawn in place, with its trunk diameter, dripline, ring and any no-dig zone.
• How roots are found before they’re cut. CSU lists hand digging, an air spade, or a backhoe operator who knows when he hits roots and stops. A good answer names one.
• What happens at a large root. A good answer: the crew stops and the edge moves.
• No root-absorbed or extended-control herbicide in the root zone.
• Where machines drive and material sits. CSU bars parking and stockpiling in the protected root zone; see preparing for installation day.
• How the tree gets water afterward, and where its leaves will go (leaves on artificial turf).

Done well, the turf ends at a clean edge well outside the trunk, the ring sits at its original grade under a few inches of mulch, no roots are left exposed or buried, and the tree waters on its own schedule. More installer questions: questions to ask a turf installer and artificial turf installation.