NC Cooperative Extension Resources

Homeowners and professional landscapers depend on mulch in the ornamental plantings for several reasons. Functionally, mulches discourage weeds from growing, conserve moisture during drought periods, allow better use of water by controlling runoff and increasing water-holding capacity of light, sandy soils. Mulches help maintain a uniform soil temperature. A 3- to 4-inch layer of mulch can add to the aesthetic value of a garden while protecting the base of plants from being injured by mechanical equipment.

Many organic materials can be used as a mulch. North Carolina gardeners use pine needles, pine bark, compost, peat moss, and decayed sawdust. Most of our landscape plants benefit from working organic matter into the root zone area. This could include all the previously mentioned materials (except pine needles) and also manure, composted wood shavings, tobacco stems, and lawn clippings.

Mulch can be applied just about any time of the year when trees and shrubs are being planted. The best time, however, to apply mulch in established bed areas would be in mid-spring when soil temperature has warmed up enough for sufficient root growth. If applied earlier, the mulch will keep the soil temperature lower and root growth possibly delayed.

Mulches should be applied 3 to 4 inches in depth over relatively clean, weed-free soils. Don't make the mistake of just covering bermudagrass, nutgrass or other perennial garden weeds with a layer of mulch. Identify and eradicate the weeds before the mulch. Use a directed spray of a recommended herbicide and then apply the organic material. It will not be necessary to pull the mulch back every time you fertilize or water. If the mulch you use is not completely decayed incorporate 2 to 4 lb of 10-10-10 per 100 square feet of mulched area. This is especially true for wood chips, sawdust and shredded bark.

Several inorganic materials are often used as mulches. These might include gravel, rock or black plastic. Be certain that the gravel, stones or lava rock coincide with the overall design. Often they are not compatible landscape components. Black plastic will discourage weeds but at the same time interfere with the normal oxygen and water supply to the roots. When the plastic is used a very shallow root system is created and during drought periods the plants may not withstand the stress. Therefore, it is recommended not to use black plastic around ornamentals. There are, however, several landscape fabric mulch products available that will function the same as plastic, but allow for normal water and oxygen exchange. These materials are placed on bare soil around trees and shrubs with the mulches used on top. There are many brands and types of materials from which to choose. They have proven to be beneficial in discouraging weeds and holding soil moisture. Test plots using landscape fabric in conjunction with organic mulch materials were rated the best of other mulch treatments. A 3- to 4-inch layer of organic matter maintained on weed-free soil will be both functional and aesthetically pleasing.

Table 1. Relative value of mulches.
1 = Excellent, 2 = Good, 3 = Fair, 4 = Poor, 5 = Unsatisfactory
Aesthetic Value Source of Weeds Resists Wind Blowing Resists Compaction Availability Comments
Organic Materials
Compost 2 3 1 2 2 Depends on ingredients
Lawn Clippings 4 3 2 4 1 Should be composted
Leaves 2 2 4 5 1 Should be composted
Manure 5 5 1 2 3 Good only for incorporation into soil
Peat Moss 1 1 2 2 1 Readily available; expensive
Pine Needles 1 1 2 1 1 Excellent mulch; easy to handle
Bark Granules 1 1 1 1 1 Excellent mulch; generally used in large amounts
Wood Shavings 3 1 2 2 3 Good for incorporation; add nitrogen
Sawdust 3 1 2 2 3 Should not be too deep; beware of crusting over
Waste Paper 5 1 5 2 1 Not recommended when used alone
Inorganic Materials
Black Plastic 5 1 5 1 Must anchor but not recommended
Gravel 3 1 1 1 1 Must be compatible with design
Crushed Rock 2 1 1 1 1 Must be compatible with design
Lava Rock 2 1 1 1 3 Must be compatible with design

Author:

Extension Agent, Agriculture
Camden County

North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.

Publication date: June 30, 1994