Besides using plants to deter weed growth, synthetic mulches are also effective tools for suppressing weeds. The best time to install plastic mulches or landscape fabrics is when you’re installing a new planting. Black plastic sheeting (polyethylene), or spunbound, woven, or nonwoven landscape fabrics (polypropylene or polyester) are available. Black plastic suppresses weeds better than fabric in some cases, but landscape fabrics last longer, allow water to drain through, and are sold in sheets of convenient sizes that may be easier to use. In fact, some fabrics are precut into “tree circles” that provide a circular weed-free area beneath trees. All these synthetic mulches are degraded by sunlight and should be covered with a 2-inch layer of organic mulch or some sand or gravel, to protect them. They can last from 5 to 10 years or sometimes even longer.
In addition to synthetic mulches, organic mulches should be part of your initial and ongoing IWM program. Coarse mulches, like large bark chips, should be used in areas of high rainfall, because they allow water to drain quickly. Deep mulches are more effective at controlling weeds than shallow ones. As a rule, organic mulches should be 2 to 4 inches deep, and they should not come in direct contact with the trunks of trees or the crowns of plants.