The Importance of Mulcing

Q: I keep hearing about the importance of putting mulch around plants. Why? What are good sources? Are there good or bad mulches?

A: Mulching is simply the process of covering the soil, yielding many benefits. It increases organic matter and water-holding capacity.  It acts as an insulator and stabilizes soil temperature, helps to minimize weeds, prevents erosion and protects tree trunk damage from lawn equipment. Organic mulches include straw, woodchips, bark, shredded leaves, grass clippings and newspaper. Synthetic mulches don’t breakdown nor add any nutritional value to the soil.

When mulching annuals and perennials, first weed your garden: mulch is most effective as a weed barrier when the garden is clean. Next, select mulch that breaks down quickly so perennials and bulbs can break through the surface. Fine mulch is also easier to work back into the soil after it has decomposed.  A 1 to 2 inch depth should be sufficient for perennials and 1-inch for vegetables and annuals. Thick mulch around shallow- rooted plants like rhododendrons and azaleas should be avoided.

Mulching is one of the most beneficial things you can do for your trees, but too much can have damaging effects. Apply no higher than 2 to 3 inches above the ground otherwise roots may suffer from a lack of oxygen and may migrate to the surface to “breathe” where they are prone to injury.  Pull mulch away from the base of trees and shrubs about 4 to 5 inches, exposing the root flare or crown. This will prevent rot damage to the bark due to constant moisture retention. Ideally you should mulch out to the drip line of the furthest reaching branches or even beyond if space permits.

The best time to mulch depends upon you: some prefer fall. Trying to navigate around emerging spring bulbs can be bothersome. In any event it should be done whenever the existing mulch decomposes.  New plantings should be mulched immediately.
Avoid peat moss or compost since these materials may favor weed growth and are best used as soil amendments. Fresh organic matter such as pine bark, sawdust and wood chips need time to cure since they have the potential to draw nitrogen from soil. Use mulch that is partially decomposed. A mulch of pine needles may be used on most plants but are especially good around evergreens, azaleas, rhododendrons, mountain laurel, andromeda, abelia, blueberries and other acid-loving plants. As with most things, if it smells sour, don’t use it. Sour mulch has fermented and contains compounds that can harm plants. Aerate the pile and allow drying before using. For additional tips, please contact your local Cooperative Extension or visit (http://www.gardening.cornell.edu/).

Mootsy Elliot
Grand View on Hudson Master Gardener with Cornell Cooperative Extension of Rockland