Gravel for a Greenhouse Floor: Best Stone, Depth and Tons
Choosing gravel for a greenhouse floor comes down to three jobs: carry away the water that drips off benches and hoses every day, give you a firm, level surface to walk and wheel on, and keep weeds from coming up between the pots. A good stone floor does all three for years with very little upkeep. This guide compares the stones that work, shows how deep to lay them, explains how to build the base under a kit greenhouse and walks through how many tons to order for common greenhouse sizes.
Open the gravel calculator →The short answer
- Best all-round floor: 3 to 4 inches of clean 3/4-inch crushed stone (such as #57) over landscape fabric. It drains fast and stays put.
- Softer to walk on: 2 to 3 inches of pea gravel over a thin crushed-stone base, held in by an edge.
- Under the frame: 4 inches of compacted crushed stone that is dead level, wider than the greenhouse by about 6 inches all round.
- Main walkway: pavers or a strip of compacted stone if you push a wheelbarrow or cart.
- Tons = length × width × depth in inches ÷ 12 ÷ 27 × about 1.4.
Related: How Much Pea Gravel for a 12x20 Greenhouse Floor?
Why gravel works well in a greenhouse
A greenhouse floor gets wet on purpose. Watering, misting and run-off from benches all land on the ground, and a floor that cannot shed that water turns muddy, grows algae and gets slippery. Clean stone has open space between the pieces, so water drops straight through to the soil below instead of sitting on top. It also gives a level surface for benches and shelving, keeps soil from splashing onto low pots and, laid over fabric, holds back most weeds. Many growers also wet the floor on hot days to raise humidity; a stone floor takes this well because it drains again quickly.
Best gravel for a greenhouse floor, compared
- 3/4-inch clean crushed stone (#57). Angular pieces that lock together into a firm floor and drain very well. The best general choice, and the best base under any other surface. See our guide to #57 stone for sizes and uses.
- Pea gravel. Small rounded stones that are pleasant to walk on and look tidy. They roll under foot and under bench legs, so lay them thin over a crushed-stone base and keep them inside an edge. Our page on a pea gravel patio covers edging and depth in more detail.
- Crusher run or dense-grade base. Stone mixed with fines that compacts nearly as hard as pavement. Good for the pad under the frame and for a hard walkway, poor as a full floor because water drains through it slowly.
- River rock. Drains well but is lumpy, hard to set pots on and awkward to sweep. Better used as a drainage strip outside the walls.
- Stone dust or screenings. Packs smooth but can hold a wet film on top and grow moss in a humid house. Use only as a thin setting bed under pavers.
Whatever you choose, ask for washed stone. Unwashed gravel carries fine material that fills the gaps, slows drainage and turns green in damp air; our guide to washed vs unwashed gravel explains the difference.
Related: How Much Pea Gravel for a 10x10 Greenhouse Floor?
How deep should gravel be in a greenhouse?
- Floor inside a greenhouse on good ground: 2 to 3 inches of clean stone over fabric is enough.
- Clay or wet ground: 4 inches or more of clean stone, and slope the ground under it so water can leave the footprint.
- Base under the frame or walls: about 4 inches of compacted crushed stone, set level. On soft ground or for a large structure, go deeper or use a concrete or timber footing as the kit maker recommends.
- Pea gravel top layer: 1.5 to 2 inches. Deeper pea gravel is harder to walk through and shifts more.
Gravel base for a kit greenhouse
Most hobby greenhouses, whether polycarbonate, glass or a hoop house, need a base that is level, square and stable so the frame does not twist and the doors keep closing. A gravel pad does this well and is easier to build than a slab.
- Mark the footprint about 6 inches wider than the greenhouse on every side.
- Strip sod and topsoil down to firm subsoil, and grade the ground so it sheds water away from the site.
- Build a perimeter of treated timbers, blocks or pavers to contain the stone and give the frame something solid to fasten to.
- Lay fabric across the whole area to separate the stone from the soil and slow weeds. Our page on landscape fabric under gravel covers which kind to use.
- Spread crushed stone in 2-inch lifts and compact each one with a plate compactor or hand tamper until it stops moving.
- Check level both ways with a long straightedge and fix high and low spots before the frame goes on.
- Anchor the frame the way the manufacturer says. Greenhouses are light and catch a lot of wind, so ground anchors or footings matter more than the stone.
The same method used for a gravel shed foundation works here; the main difference is that a greenhouse floor stays wet, so drainage under and around it matters more.
Walkways, benches and staging
- Walkways: a central path of pavers or flagstones set on compacted stone is easy to sweep, keeps carts from sinking and gives you a dry place to stand. Use the paver calculator to count pieces, and see how deep a paver base should be.
- Under benches: leave plain gravel so drips from the benches drain straight through.
- Gravel trays on staging: shallow trays of pea gravel or grit kept damp on benches add humidity around the plants, and pots on top sit above the water rather than in it.
How much gravel do I need for a greenhouse?
- Area (sq ft) = length × width. Add the extra 6 inches each side if you are building a pad under the frame.
- Volume (cu yd) = area × depth in inches ÷ 12 ÷ 27.
- Tons = cubic yards × about 1.4 for crushed stone or pea gravel. Use your supplier’s figure if they give one.
- Add 5 to 10 percent for compaction and uneven ground.
Worked examples at 3 inches deep and 1.4 tons per cubic yard, before the extra for waste:
- 6 × 8 ft (48 sq ft): 12 cu ft, about 0.44 cu yd, roughly 0.6 tons.
- 8 × 10 ft (80 sq ft): 20 cu ft, about 0.74 cu yd, roughly 1 ton.
- 10 × 12 ft (120 sq ft): 30 cu ft, about 1.1 cu yd, roughly 1.6 tons.
- 12 × 20 ft (240 sq ft): 60 cu ft, about 2.2 cu yd, roughly 3.1 tons.
A 4-inch pad under a 10 × 12 greenhouse, widened to 11 × 13 feet, is 143 square feet: about 47.7 cubic feet, 1.8 cubic yards or roughly 2.5 tons. Small jobs like these are often easier to buy by the bag or the scoop than by the truckload. Run your own numbers in the gravel calculator or the crushed stone calculator.
Keeping a gravel floor clean
- Sweep or rake up spilled potting mix and plant debris often; organic matter in the stone feeds weeds, moss and pests.
- Rinse or wash down the floor between growing seasons so the gaps stay open.
- Pull any weeds while small, before roots work through the fabric.
- Top up thin spots and re-level under bench legs once a year.
Common mistakes
- Building on a low spot, so outside water flows in under the walls.
- Using stone with lots of fines, which seals the floor and grows algae.
- Laying deep pea gravel with no base or edge, so it shifts and bench legs sink.
- Skipping fabric and fighting weeds every season.
- Setting a frame on a pad that is not level, which racks the frame and jams the doors.
Questions people ask
What is the best gravel for a greenhouse floor?
Clean, washed 3/4-inch crushed stone such as #57 is the best all-round choice because it drains quickly and locks into a firm surface. Pea gravel is softer underfoot and works well as a thin top layer over a crushed-stone base.
Is pea gravel good for a greenhouse floor?
Yes, as long as it is laid thin, about 1.5 to 2 inches, over a firmer base and held in by an edge. Deep pea gravel shifts under foot and lets bench legs sink.
How deep should gravel be in a greenhouse?
About 2 to 3 inches of clean stone over landscape fabric suits most floors on firm ground. Use 4 inches or more on clay or wet ground, and about 4 inches of compacted crushed stone for a pad under the frame.
How much gravel do I need for a 10x12 greenhouse?
A 3-inch floor over 120 square feet is about 1.1 cubic yards, or roughly 1.6 tons at 1.4 tons per yard. Add 5 to 10 percent for compaction and uneven ground.
Should I put landscape fabric under gravel in a greenhouse?
Usually, yes. A woven or non-woven landscape fabric keeps the stone from mixing into the soil and slows weeds, while still letting water drain through.
Can you put a greenhouse directly on gravel?
Many kit greenhouses can sit on a level, compacted gravel pad with a timber or block perimeter. Follow the manufacturer's base and anchoring instructions, because light frames need to be tied down against wind.
Related guides
- Gravel shed foundation
- Landscape fabric under gravel
- Crushed stone vs gravel
- How much a yard of pea gravel weighs
- Gravel for a chicken run
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