Spreading Pea Gravel Mulch 3 to 4 Inches Deep in a High-Desert Xeric Bed by Wheelbarrow: Half-Inch Stone, No Fabric, and Half-Full Loads

 

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Wood mulch blows off a high-desert bed in the first spring wind and sits there as fuel near the house. Small gravel stays put, lets the summer storms soak in, and does not burn.

For a dry-climate bed, use stone no bigger than about half an inch, spread 3 to 4 inches deep straight on the soil with no landscape fabric. One cubic yard covers about 108 square feet at 3 inches or 81 at 4. Move it in half-full wheelbarrow loads so the barrow stays steerable.

Why small gravel and not river rock

Colorado State University Extension's garden notes on mulching say gravel under one centimeter across has been shown to suppress weeds and cut evaporation about as well as wood chips. They add that landscapes in dry climates are the most likely to benefit from gravel mulch.

The same notes say stones must be no more than around a half inch in diameter to work as mulch, and larger rocks increase runoff. Pea gravel, by contrast, improves water infiltration in short, hard storms, and a three-inch layer can increase infiltration manyfold.

That matters on a high-desert lot, where most of the summer rain shows up in a few violent thunderstorms. Fist-sized cobble looks tidy, but the water runs off it.

No fabric underneath

CSU's fact sheet on mulches for home gardens says correctly applied mulch does not need landscape fabric, and fabric is often detrimental to plant and soil health. It gives a depth of 3 to 4 inches for most mulches, pea gravel included.

The classic mistake is putting fabric down first and gravel on top. Wind drops dust into the gravel, weeds root in that dust on top of the fabric, and the fabric shreds the first time you try to plant through it.

Figuring how much to order

1. Measure the bed and multiply length by width for square feet.
2. Divide by 108 for a 3-inch layer, or by 81 for a 4-inch layer. That is cubic yards.
3. Round up a little. Gravel settles into soft soil on the first watering.

A 10-by-20-foot bed at 3 inches comes to about 1.9 cubic yards, so I would order 2. At 4 inches it is about 2.5 yards.

Moving it without wrecking the wheelbarrow

Gravel is heavy, roughly 100 pounds per cubic foot. A heaped load in a 6 cubic foot steel wheelbarrow would weigh far more than anyone should push, so I fill mine about half full.

1. Have the gravel dumped on a tarp as close to the bed as the truck can reach.
2. Shovel about 3 cubic feet into the tub, keeping the load slightly forward over the wheel.
3. Lay a plank over soft soil or lawn so the tire does not sink.
4. Dump in small piles across the bed, about a load every few feet, rather than one big mound.

At half loads, a cubic yard is about nine trips. It goes faster than it sounds, and you still have a back at the end of the day.

Spreading to depth

1. Pull the piles flat with the back of a steel rake.
2. Push a ruler into the gravel in a few places to check depth.
3. Keep gravel a few inches back from plant crowns and tree trunks.
4. If the bed sits next to a walk, lower the soil 3 inches before spreading so the top of the gravel lands at grade. The CSU notes suggest this to keep mulch from spilling out.

The CSU fact sheet also notes gravel transfers more heat to the soil than wood chips, and its warming effect can reach a foot down in cold months. That is a plus for many xeric plants in a cold-winter climate, but keep heat-sensitive plants out of a gravel bed against a south wall.

Where the gravel comes from

Home Depot and Tractor Supply sell bagged pea gravel, which is fine for a small bed. For anything over a yard, a local landscape supply yard delivering in bulk costs far less.

For the same barrow routine with wood chips around trees, see this walkthrough on wheeling wood-chip mulch rings around young yard trees.