What Should I Put in a Flower Bed Before Mulch to Keep Weeds Out?

Plastic

• Black plastic mulch is unattractive in flower beds on its own, but the addition of wood chips or another organic mulch hides it from view. Plastic prevents most weed growth and retains moisture in the soil. It is an inexpensive option for use in annual beds, but it tears and breaks down within one to two years and requires replacement. Plastic doesn't allow water or air penetration to the soil so it's best to install it over a drip irrigation system to ensure the soil and plants receive the necessary moisture.

Fabric

• Fabric mulches, sometimes called geotextiles, provide a longterm underlayment option in flower gardens. The fabric last for five or more years when it's covered with an organic mulch. Fabric doesn't prevent weeds as well as plastic, since some light still penetrates the mulch layer and allows seed germination. Using a 2-inch depth of organic mulch over the fabric prevents most light penetration, allowing the fabric to block weed growth more successfully. Fabrics allow water and air penetration so they do not require drip irrigation.

Newspaper

• The lowest cost and most readily available option is newspaper. Layer the newspaper at least 10 sheets deep over the garden bed to prevent most weeds. Weeds can grow between the sheets, but overlapping the edges prevents the breaks in the mulch layer that allow weed growth. Newspaper works best in established beds with few weeds, as some weeds will penetrate the paper layer. The newspaper sheets break down over the coarse of the season, adding organic matter to the soil but necessitating reapplication each spring.

Installation Method

• Proper installation allows the plastic, fabric or newspaper to block weeds without blowing up in windy weather. Lay the underlayment before planting when possible. Dig a trench around the edge of the bed and push the edges of the underlayment into the trench. Refill the trench with soil to anchor the edges of the sheet mulch so it doesn't pull up. Cut the planting holes directly in the sheet mulch layer and plant the flowers as usual. Cover the underlayment with a 2-inch layer of organic mulch. A layer of this thickness further helps prevent weeds and keeps the underlayment mulch from showing through the more attractive organic mulch.