Rock Mulch

Mulching is a must in Colorado, for several reasons. Mulching minimizes evaporation. It cools plant root zones and reduces the amount of water the soil loses through evaporation. It reduces weed growth, and it helps control erosion. Mulch also adds a finished look to the garden.

Rock mulch is an excellent choice where a more formal look is desired, or in locations where wind can blow away wood-based mulches. Rock mulch doesn't blow away and rarely needs to be replaced, but it tends to retain and radiate heat so it's not the best choice to go along the sunny side of a house. It's also not a good choice around heat-sensitive plants. On the other hand, dryland plants with hairy leaves and succulent stems do much better in rock mulch than in wood-based mulch, which keeps the soil too moist and promotes root rot.

Since rock mulch is hard to move around, it works best in a settled garden bed, where plants won't be moved and replaced frequently.

Black gravel mulch contrasts with foliage.

Avoid using limestone or marble, since they contain calcium carbonate which will alter the soil pH, resulting in yellowing of plant foliage.

Rock mulch may be applied directly on top of the soil or over a weed barrier fabric,* and should be layered two to four inches deep.While use of a weed barrier fabric will reduce weeds, over the course of several years dirt and debris will collect in the rock and weeds will appear on top of the fabric, so some weeding will be required.

* Never apply mulch over black plastic. Plastic doesn't allow moisture or air to penetrate, and it can kill useful organisms in the soil.