Decomposed granite is like gravel, but finer and generally more stable. It’s formed from the natural weathering and erosion of solid granite, a tough, hard, igneous rock. The DG sold as landscaping material is typically composed of fine 3/8-inch (or smaller) particles; some may be no bigger than a grain of sand. Colors vary, from buff to brown, and include various shades of gray, black, red, and green.
Although there are at least 30 colors and varying degrees of particle sizes, decomposed granite basically comes in three forms: natural, stabilized, and resin-coated:
- Natural DG is used as a mulch material and can be spread around trees and garden beds much like wood mulch. It will continue to weather after it is put in place and provides nutrients to surrounding soil and plants. It lasts longer than most other mulch materials and will not attract pests.
- For a path or patio, DG with stabilizers (which serve as a binder) is the best solution. Stabilized DG is often added on top of another gravel material, tamped down, then left with a thin loose layer on top.
- DG with resin for driveways has a similar surface to asphalt, but has a more natural look and is permeable.
While DG is most commonly used for paths, driveways, garden trails, and as a xeriscape ground cover, it can also be used to create smooth visual transitions between formal garden and wilderness. One of its advantages is that it breaks down, so any DG that migrates into lawn or planting beds does not cause problems the way gravel does. Lining a path or patio with a black metal strip (which will disappear if buried low enough) will help keep it in place.
One caveat: Make sure not to install the material too close to a house or building. It does stick to shoes, and will scratch floors. This can be avoided by separating the DG from the home with a few feet of other surface materials, plus a door mat.
The raw material costs $35/yard. The cost to have a contractor install a path or patio is approximately $4-$6 per square foot, depending on conditions and whether stabilizers are added. If you do it yourself, the cost will be about half that amount.
For a resin-coated DG driveway, which has a surface much like asphalt (but is permeable), the cost is higher. A local driveway installer is the best source for cost information.
- Has some of the advantages of gravel–the crunchy sound, the softened look, the permeability–without some of the disadvantages: it remains firm underfoot.
- As it starts to weather and erode, it’s simple to add more.
- Soft, natural appearance.
- Can be used to smooth transitions between garden and wilderness.
- Provides good drainage.
- Excellent mulch material.
- Sticks to shoes–different surface materials are needed near house, plus a doormat, to keep material out of house (will scratch floors)
- Good solution under large trees where grass won’t grow.
- Keeps dust down.