IDEAS for Landscaping with Rocks

Mulch choices depend on multiple factors.

Mulches give the landscape a finished look while also minimizing maintenance in garden beds. Lava rocks supply a durable and attractive choice, but they aren’t suitable for all garden areas. Deciding on whether to use lava rocks or an organic mulch, such as bark, in the landscape depends on the types of plants you are growing, the amount of upkeep preferred and your aesthetic preferences.

Permanence

Organic mulches require annual replacement because they break down and decompose, eventually adding organic matter and nutrients into the soil. Bark and wood nuggets must be maintained at a depth of 2 inches to provide the best benefits, so fresh mulch must be added on top at least once a year to maintain this depth. Lava rocks never break down so they do not require replacement. Usually a weed barrier is used beneath rocks. A fabric barrier may require replacement every 10 years if the fabric begins to tear and allow weeds to grow through. Once installed, lava rocks are more difficult to remove than other mulches.

Weed Suppression

Lava rocks provide optimum weed suppression as long as the fabric barrier beneath the rocks remains in good repair. Organic mulches do suppress weeds, although some weeds can grow through the mulch or within the mulch, especially as the layer begins to break down. The few weeds that do penetrate lava rocks require prompt removal or they can destroy the fabric underlayment and cause further weed issues later. If soil collects on top of the fabric and beneath the rocks, some weeds may take root in this soil layer.

Maintenance

Bark and wood mulch requires regular maintenance. Not only does the mulch require annual reapplication, weeding is sometimes necessary as often as once a week to prevent them from establishing. Even if the mulch layer doesn’t break down yearly, a fresh layer is necessary to keep it looking its best since it will weather. Lava rocks only require infrequent weeding. Leaves and debris can build up on the rock surface, requiring periodic leaf blowing to remove the debris from the rock surface. The fabric barrier beneath rocks also requires replacement once it begins to tear and break down.

Other Benefits

Both lava rocks and mulch can retain moisture in the soil, resulting in less frequent watering. Unlike rocks, bark and other organic mulches improve the soil quality as they break down. Lava rock helps provide optimum drainage to a bed, making it a suitable choice for low-lying areas that collect water or for plants that prefer drier growing conditions.

Selection

Select lava rocks in areas where you want minimal maintenance and plan to grow native or low-maintenance perennial shrubs, trees and plants. The rocks are best for areas where the ground is rarely disturbed and where the rocks can remain as a permanent part of the landscape. Organic mulches are best suited to perennial and annual flower beds where the plants are frequently moved or replanted.