Simple Facts About Mulch

Bennett Joffrion, Fletcher, Jr., Bobby H., Razi, Sam S.  |  10/20/2007 1:31:43 AM


A mulch layer around trees, shrubs and planted beds and covering bare ground provides many benefits. In areas that are difficult to mow, irrigate or otherwise maintain, use mulch to replace turf or groundcovers. Also consider placing mulch in shady areas where plants don’t grow well.
  • Organic mulch materials improve soil fertility as they decompose.
  • Mulch buffers soil temperature, keeping soils warmer in winter and cooler in summer.
  • Mulch helps maintain soil moisture by reducing evaporation. A layer of mulch also minimizes water needs for established plants.
  • Fresh mulch inhibits weed germination and growth.
  • Over time, many types of mulch improve soil aeration, structure and drainage.
  • A mulch layer can inhibit certain plant diseases.
  • Mulch around trees and shrubs (not against the trunk) eases maintenance and reduces the likelihood of damage from string trimmers.
  • Mulch gives planting beds a neat and uniform appearance, adding a contrast of color and texture that complements plantings.

Guidelines for Using Mulch

Follow these tips when adding mulch to your landscape:

  • For well-drained sites, apply a 2-inch to 3-inch layer (after settling) of mulch around trees, shrubs and bedding plants. If there are drainage problems, use a thinner layer. Coarse materials, such as pine nuggets, may be applied to a depth of 4 inches, but don’t allow mulch to accumulate to a greater depth. If mulch is already present, check the depth. Do not add mulch if there is a sufficient layer in place (2 inches to 3 inches).

  • “Volcano mulching,” or mulch applied too deeply, hinders oxygen exchange to roots, which stresses the plant and causes root rot. Do not place mulch on top of a tree’s root ball or against the trunk. More than about 1 inch of mulch on the root ball of newly planted trees and shrubs can stress plants because mulch can intercept water meant for the roots.

How Much Mulch?

Bulk quantities of mulch are sold in cubic yards. To calculate the amount of mulch you need, first measure the area to be mulched, in square feet. Next convert the desired depth to a fraction of a foot. For example, 3 inches divided by 12 inches equals ¼ foot or 0.25 foot. Multiply this fraction by the square-foot measurement of the area to be covered (.25 foot x 100 square feet = 25 cubic feet). Convert cubic feet to cubic yards by dividing cubic feet by 27 (25/27 = .926). To cover a 100-square-foot area to a depth of 3 inches, you will need .926 cubic yards.

  • If mulch is piled against a tree trunk, pull it back several inches to uncover the base of the trunk and the root flare. Mulch piled against tree trunks holds moisture against the trunk and stems, and trunks that remain constantly wet are prone to root rot. Mulch piled high against the trunks of young trees may also create habitats for rodents that chew the bark and can girdle the trees.

  • Mulch out to a tree’s drip line or beyond -- at least an 8-foot diameter around the tree. Remember that in a forest environment, a tree’s entire root system (which usually extends well beyond the drip line) would be mulched.

  • Thick blankets of fine mulch can become matted and may prevent water and air from seeping through or become like potting soil and support weed growth. Rake old mulch to break up any matted layers and to refresh the appearance.

  • Organic mulches may require weeding and replenishment once or twice a year to maintain a total depth of 2 inches to 3 inches.

  • Do not use cypress mulch because harvesting from the wild depletes wetlands.

  • Shell, crushed stone or pebbles can be used as mulch, but they won’t contribute to the soil’s nutrient and organic content or water-holding capacity. Limestone and shell both raise soil pH. They also reflect heat, increasing the water needs of plants.
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