Can You Put a Pergola on Artificial Turf?

This page is for homeowners who want a pergola over a turf lawn, or over a lawn about to become turf. Pergola sellers often say a lawn is fine. Turf guides say nothing about posts. We read the anchoring rules from three pergola makers, put them in one table, and worked out what they mean for a turf yard.

Key takeaways

• A pergola must be bolted down. Every maker we read says so, and none offers a way to stand posts on soft ground.
• A turf base is 3 to 4 inches of crushed rock. A pergola footing is 24 to 42 inches of concrete. The base is not a foundation.
• The base also slopes 1 to 2 percent. Across the 9.5 ft between posts on a 12 x 12 kit, that is 1.1 to 2.3 inches out of level.
• A 4-post 12 x 12 pergola needs four holes and 6 to 32 cu ft of concrete, depending on the maker's footing.
• Footings go in first. The turf goes in last and is cut around each post base.

What is a pergola, and what holds it up?

A pergola is an open garden frame. Four or more posts carry beams, and the beams carry rafters or slats overhead. It has no walls and no solid roof. Even so, it is tall and top-heavy, and wind pushes on it and can try to lift it.

What holds it up is the footing. A footing is a block of concrete poured into a hole under each post. A steel bracket, called a footplate or post anchor, is bolted to the top of the concrete, and the post is bolted to the bracket. In cold places the footing must reach below the frost line, the depth the ground freezes to in winter. Freezing soil swells and can heave a shallow footing up out of the ground.

A turf base is the crushed rock under a turf lawn. Our base preparation guide puts it at 2.5 to 4 inches, compacted, with the top graded to slope 1 to 2 percent so rain runs off. It is firm enough for feet. It is not a footing.

Why can't the posts stand on the turf or its base?

The makers require anchoring. The Outdoor GreatRoom Company's Sonoma 12 manual says "Anchoring Required" on its first page. Forever Redwood says "All posts should be attached to the ground." The Pergola Kits USA manual says the entire bottom of each column must sit on "a flat, solid concrete slab or footing" or a wood or composite deck. Turf is none of those.

The base is too thin to hold a bolt. Pergola Kits USA drills a 5 inch deep hole in the concrete for each wedge anchor. Forever Redwood uses 1/2 x 4 inch anchor bolts in 4 inch holes. A turf base is 3 to 4 inches deep in total, and it is loose rock, not concrete. No anchor bolt grips it.

The base is too shallow to resist wind and frost. The shallowest footing we found is 24 inches. A 4 inch base is one sixth of that. In cold places the gap gets wider, with footings at 42 inches or below the frost line.

The base is not level. Pergola Kits USA says to make sure the column marks "are level with each other," then uses a mason line so the column tops are level. The Sonoma manual says to anchor the posts only after the frame is "in position, squared up, and leveled." A turf base is built to slope. Across the Sonoma's 114 inch post spacing, a 1 percent slope drops 1.1 inches and a 2 percent slope drops 2.3 inches.

Pavers and stones are ruled out too. Pergola Kits USA says not to seat columns on "pavers, stone, tile, stamped concrete, or uneven concrete." Forever Redwood does not recommend attaching to paver, stone or flagstone patios, and pours footings instead. So a stepping stone set into the turf is not a post base either.

Why do so many pages say grass is fine?

Because on grass the posts still go on footings. The Sonoma manual's post drawing shows a footing under each post, and it labels that detail "Suggested for installation on lawns." The lawn is fine because the concrete goes down through it. Nobody means the posts sit on the grass.

Turf changes one thing: the order. Grass grows back to the concrete by itself. Turf is a finished layer over a rock base, so the footings have to go in before the base, or you cut through a new lawn later.

How big are pergola footings? Three makers compared

A Sono-tube is a cardboard tube set in the hole as a form, so the concrete comes out as a neat round column.

Forever Redwood's high-wind kit is rated for winds up to 150 mph, and its table runs 30 inches deep for the smallest post and 42 inches for the largest. It also gives the only cure time we found: "Allow up to 3 days for the concrete to cure" before the anchors go on. Its footings are poured flush with the ground, or 1/2 inch above it "if you do not want the posts to wick up moisture."

The three makers agree on the main rule. They differ on size, and the hole you dig should follow your own pergola's manual and your local code.

How much concrete does a 4-post 12 x 12 pergola need?

The Sonoma 12 is about 12 ft across the roof (146 x 151.5 inches at most). Its four posts stand 114 inches apart, center to center. So the job is four holes about 9.5 ft apart.

Here is our arithmetic for one hole and for four. Round holes are worked as straight-sided columns. Bags are 80 lb bags of concrete mix at 0.6 cu ft each, our figure from the basketball hoop footing page, plus two spare.

The Pergola Kits USA footing is about 1.2 cu yd for four holes. That is 4,480 lb of dry mix in bags, so at that size it may be easier to order ready-mixed concrete.

Compare that with the turf base under the same pergola. The posts enclose about 9.5 x 9.5 ft, or 90 sq ft. At 3.5 inches, the base there is about 26 cu ft of compacted rock, spread in a thin sheet. The four footings hold 6 to 32 cu ft of concrete in deep columns. The base spreads the load of feet. A footing anchors one post.

What order do you build the footings and the turf in?

Footings first, base second, pergola third, turf last.

1. Check your local rules. The Sonoma manual says to contact your local authority, and Forever Redwood has its engineer set the footing design. Call 811 before you dig.
2. Dig out the turf area to subgrade, the firm soil under the base.
3. Mark the post centers. Pergola Kits USA squares them with two strings run corner to corner. The two lengths must be equal.
4. Dig each hole from the subgrade. Our rule: measure the depth from there, so the base adds a few inches of margin on top.
5. Set the forms and pour. Set all four tops at one height. Wait for the concrete to cure: up to 3 days per Forever Redwood.
6. Build the base around the footings in lifts. Hand tamp near the concrete.
7. Assemble the pergola and bolt it down, while ladders stand on rock, not new turf.
8. Lay the turf and cut it around each post base. The rest of the turf job is in how to install artificial turf.

Do not tilt the footings to follow the lawn. The posts are cut to one length, and the makers want them level.

How do you cut the turf around the pergola posts?

Lay the turf in its final place, then cut each post base out from the back. Make a relief cut along a stitch row from the nearest edge, on the side seen least, and close it with seam tape later, as in seaming. The method is the one in cutting around obstacles.

Treat each footing as a hard edge, the way our edging and borders guide does. Set the base so the turf backing sits 1/2 to 3/4 inch below the top of the concrete. That matches Forever Redwood's advice to pour 1/2 inch above the ground, so the post stays dry. Keep the turf on the concrete edge, never wrapped against the wood post or its trim. Nail 1 inch outside the concrete, every 3 to 4 inches. An 18 inch footing is about 4.7 ft around, so that is about 16 nails.

Adding a pergola to an existing turf lawn. Pull the nails near each post spot, cut from the nearest seam or edge, and fold the turf back. Dig through the base and down to footing depth, pour, and let it cure. Rebuild the base around the concrete, hand tamp it, then lay the turf back and cut around the post base.

Where can pergola posts go in a turf yard?

What this page does not cover

This page covers freestanding pergolas on four or more posts over a turf lawn. It does not size footings for your yard. Hole depth is set by your pergola's manual, your local code and your frost line, and those outrank every figure here. A pergola fixed to the house wall, a louvered roof, a solid roof or a wood deck changes the loads and the rules, so follow that maker's drawings and your inspector. If the posts sit near the house, the ground still has to fall away from the foundation, as covered in turf next to the house. We have not tested any anchor, and none of these makers publishes a holding force.

Sources

• The Outdoor GreatRoom Company, Sonoma 12 Pergola Manual and Installation Instructions (90224 Rev F, 01-08-19): anchoring required, footing size and depth, footplates, post spacing.
• Pergola Kits USA, Modern Fiberglass Pergola Assembly Manual (file dated 10-26-23): slab and footing minimums, surfaces not allowed, wedge anchors, squaring and leveling.
• Forever Redwood, Pergola Concrete Anchors: footing depth and width by post size, frost line, cure time, high-wind kit, pavers.

Frequently asked questions

Can I put a freestanding pergola on turf without digging?

Not one of the three we read. The Sonoma manual says "Anchoring Required," Forever Redwood says all posts should be attached to the ground, and Pergola Kits USA wants solid concrete or a deck under every column. A pergola that is not anchored can shift or tip in wind. If you cannot dig, a patio umbrella with a weighted base may suit you better.

How deep should pergola footings be in a cold climate?

Below your frost line, and deeper than in a warm yard. The Sonoma manual gives 42 inches for extreme cold. Forever Redwood says 6 inches below the frost line in snow areas. Pergola Kits USA says to follow local code and take the frost line into account. Ask your building department for the local depth, then measure from the excavated subgrade.

Can I build a pergola on a concrete slab inside a turf lawn?

Yes. Pergola Kits USA accepts a slab at least 4 inches thick and 2,500 psi, and Forever Redwood bolts its anchors to concrete. Build the slab in the same dig as the turf, before the base. The turf then meets the slab like a patio edge, with the backing 1/2 to 3/4 inch below the concrete. Do not use a paver patio as the post base.

Will a pergola keep my turf cooler?

It shades the turf under it, and shade is the most effective lasting fix on our turf too hot page. Open slats give partial shade that moves through the day, so the turf under a pergola is not shaded all afternoon. Whatever goes on top, the post footings stay the same.