Cons of Stone & Gravel Mulch

Permanence

• Gravel and stones work their way into the soil beneath, making them difficult to remove later. Laying a long-lasting landscape fabric over the soil before you install the mulch prevents the stones from mixing with the soil, but eventually the fabric will break down and begin to tear. Use the mulch only in perennial beds or beds without plants where you intend it to be permanent.

Alkalinity

• Some gravel and stone mulches are made from limestone rocks, which are highly alkaline. The alkalinity of these stones slowly dissolves and raises the pH of the soil beneath, which lowers the acidity of the site. Plants that require acidic soil can't survive once the soil becomes too alkaline. Avoid gravel mulch or use a gravel that doesn't contain limestone if you grow plants that prefer acidic soil.

Heat

• Stones absorb heat, which further warms the soil. Too much heat can cause rapid soil drying or stress the plant roots. Light-colored gravel may reflect the heat up onto the plants, cooking the foliage. Although this heat-retaining property works well for desert plants and plants that prefer dry soil, it can kill many herbaceous plants that need more moderate temperatures and moist soil. When used near the house, such as in a border bed, the absorbed heat can also cause unwanted heat in the interior of the home.

Weeds

• Some weeds can grow through the gravel mulch layer. Using a layer of landscape fabric beneath the mulch minimizes the issue, but some weed varieties may still tear through the fabric. Over time, soil may blow into the bed and collect on the surface of the fabric and the gravel layer. Weeds grow in the soil and the roots penetrate the fabric. Fallen leaves and debris also blow into the mulched area. Gravel is difficult to rake, making removal of plant debris difficult.

Safety Issues

• Gravel and stone mulches can pose safety problems. Stones that work free onto sidewalk areas can create a tripping hazard. If you use stone mulch next to lawn areas, any stone that work free from the bed and into the lawn can be thrown by a lawnmower or other lawn care equipment. Installing edging around mulched areas and keeping the layer of stones slightly lower than the top of the edging can minimize these hazards.