Mulching is one of the simplest ways to enhance your garden. It insulates the soil, protects it from erosion, conserves moisture, prevents weed growth, reduces soil compaction from heavy rain, provides a beautiful finishing touch to your garden, and may even improve soil quality. Mulching, or top dress, refers to covering the bare ground in your garden by spreading an organic material, or some sort of rock. Many materials have been tried and proven effective as mulches: ground bark, leaves, sawdust, straw, processed by-products (grape and apple pumice), and lawn clippings.

Mulch should not be confused with compost, which is a soil amendment. Mulch is used as a top dressing after plants and irrigation have been installed. Mulch covers drip irrigation, keeps the soil cooler, reduces evaporation and makes the garden look neat and tidy.

Mulch Benefits

  • Moderates the soil temperature and retains moisture during dry weather, reducing the need for watering.

  • Prevents germination of many weed seeds & reduces need for herbicides.

  • Protects the soil from the impact of raindrops that can cause crusting and prevents the germination of seedlings.

  • Adds organic matter to soil as they decompose.

  • Encourages the growth of worms and other beneficial soil organisms.

  • Mulch also can be used to enhance the look of your garden.

  • The mulch helps keep plants clean by reducing the splash of soil onto leaves during rainstorms, and helps infiltration of the rainfall into the garden.

Wood bark mulch
  • Purchase organic mulches that are guaranteed weed-free. Straw, hay, and many types of manure, for instance, may contain weed seeds.

  • Remove weeds before spreading mulch.

  • To protect plants from insects and rot, which thrive in moist conditions, keep organic mulches a few inches back from the crowns and trunks of woody plants, like trees and native plants.

  • If reapplying mulch, wait until the soil is completely warm before spreading.

  • On steep slopes where terracing is not practical, mulch areas with coarse-grade bark, which is heavy enough not to be easily blown or washed off by rain.

  • Under existing oak trees, use a stone mulch to cover the bare soil and do not plant anything, leaving the stone mulch itself as a ground cover.

  • Do not spread mulch over plastic, as plastic is an impermeable layer and will prevent any soil improvement from the mulch.

  • Lay mulch 2-3 inches thick.

  • Chop leaves with lawnmower before spreading no more than 2 inches thick.

  • Immediately after the lawn has been cut, spread the lawn clippings on the ground. Be sure the layer is no more than 2 inches. Do not wait to use the clippings as they will rot and can no longer be used as mulch. Lawn clippings can also be mixed with other garden and vegetable waste to produce compost, which then can be used as mulch.

  • Newspaper can be used along with mulch. Cover the soil with newspapers 4-6 sheets thick, layer with grass clippings to keep the papers from blowing away. Wet down with a hose and cover with chipped bark. This method is especially good for weed control. Newspapers do not contain weed seeds. If you want to plant within the area of the newspaper mulch, cut an "X" through the newspaper, fold it back, loosen the soil with a trowel, and plant. Fold the newspaper back, making sure the mulch is clear of the plant’s stem to avoid rot.

Mulch Myths

Myth No. 1: Mulch provides a permanent barrier to weeds. While mulch reduces the number of weeds, some pesky nuisances may still manage to grow through the mulch, or on top of it. Weeds will appear in new landscapes for the first year or two, even with mulch, because of the abundance of weed seeds in the soil. However, once the weeds are brought under control, fewer will follow. Organic mulch needs to be replenished when decomposed to less than 1 inch thick. The thicker the mulch the easier it is to weed.

Myth No. 2: Mulch placed against your house will attract termites. In reality, it’s moisture, not mulch, which attracts termites. So any landscaping, including shrubs, can lure the unwanted critters. Irrigation systems up against the house also create a termite-conducive environment. Even gravel or rocks around the base of a house can hold in the moisture attractive to termites.

Myth No. 3: There’s no wrong way to mulch. When mulching, keep the bark or rock one to two inches away from stems. Mulch creates a warm and humid environment that is perfect for the establishment of various fungi that can injure or kill the plants. Also, avoid covering the crown of dormant perennials.