Gardening With Allen: More mulch means fewer weeds

Polyethylene plastic should not be used as a weed barrier except for vegetables. Larger plants like trees and shrubs do not get adequate irrigation. Plant roots grow close to the surface in order to get enough oxygen. Trees and shrubs need deep, anchor roots for support.

Weed-barrier fabric acts as a physical barrier to weeds, in addition to eliminating light. It will normally last for several years as long as it is covered with granular mulch, so sunlight does not deteriorate it. A few weed seeds will eventually blow in on top of the granular mulch. However, they are very shallow rooted and easily controlled.

When black or colored poly mulches are used for larger, heat-loving vegetables, such as tomatoes, melons, squash and cucumbers, plastic strips are narrow enough so water and air can move sideways underneath the plastic, and also through holes around the plants. Poly is not covered with granular mulches because it transfers heat to the soil and reflects heat into the plants so that they grow faster.

Another advantage of organic mulches such as bark and compost is that they are converted by worms and microorganisms into humus and eventually release nutrients to the plants growing underneath them. Typically, bark and compost mulches are added every year or two. Organic mulches also improve water penetration and reduce water evaporation.

When organic mulches are used around vegetables, they are typically incorporated into the soil in the fall or early the next spring. This improves the soil and adds nutrients.

Two other readily available materials are sometimes used as mulches. Grass clippings make excellent mulch, especially for vegetables. Multiple layers of newspaper also make good mulch for vegetables. However, it is necessary to put some soil on the edges to hold it in place.