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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Organic Mulches for Gardens and Landscape Plantings

This article was published originally on 6/30/1995
While watering is often necessary during hot, dry weather, home gardeners can conserve soil moisture and reduce water usage by placing a mulch around landscape plantings and in fruit and vegetable gardens. Several organic materials may be used as mulches. The characteristics of several suggested mulches are discussed below.

Allow lawn clippings to dry before applying to garden areas. Fresh, green material will settle and form a dense mat. It may also produce an unpleasant odor. If the lawn has been treated with herbicides for broadleaf weed control, don't use the clippings until the lawn has been mowed two or three times after treatment. The best source of lawn clippings is a well-maintained lawn. Grass clippings from a weed-infested lawn will undoubtedly contain a large amount of weed seed, such as dandelion, plantain, and crabgrass. Grass clippings are not long-lasting and are best used in the vegetable garden or annual flower bed.

Straw that is free from crop and weed seed is an excellent mulch for the vegetable garden and strawberry bed. Suggested materials include wheat, oat, and soybean straw. Urban gardeners can often buy straw at garden centers. Straw may provide a winter habitat for mice and other rodents. Therefore, caution should be exercised when using straw around trees and shrubs.

Leaves are readily available in the fall. They should be shredded or composted before applied as a mulch. Shredded or partially composted leaves do not mat down as readily as whole leaves, are less likely to blow away in the wind, and decompose more quickly. Shredded or composted leaves are an excellent mulch for vegetable gardens, raspberry plantings, perennial flower beds, and around trees and shrubs. While the leaves of some trees, such as oak, are acid in reaction, they can be safely used in the yard and garden. The small amounts used by home gardeners have little effect on soil pH. Leaves are a poor winter mulch for strawberries and tender herbaceous perennials.

Pine needles are light, airy, decompose slowly, and make an attractive mulch. They may last several years and may be easily removed if necessary. Pine needles are acid in reaction and are excellent mulches for acid-loving plants, such as azaleas and rhododendrons. They can also be safely used in the vegetable garden and elsewhere in the home landscape. The best source of pine needles is a large, established windbreak.

Cocoa-bean hulls are a by-product of chocolate manufacturing companies. Cocoa-bean hulls are light, easy to handle, and have an attractive brown color. They also have a delightful aroma. (Unfortunately for chocolate lovers, the aroma lasts only for a few days.) While cocoa-bean hulls are somewhat expensive, a mulch depth of 1 to 2 inches is sufficient. Cocoa-bean hulls are excellent mulches for annuals, perennials, and roses. The material lasts about one growing season.

Shredded newspaper or whole sheets may be used in the vegetable garden. Most newspaper publishers use organic inks so gardeners need not worry about lead contamination. When placing sheets between plant rows in the garden, weigh them down to prevent them from blowing away in the wind.

Ground corncobs gradually darken as they age, becoming an attractive mulch. They are normally weed free, lightweight, and easy to handle and apply. Corncobs decompose slowly and are most often used around trees and shrubs. They are also an excellent mulch for raspberries.

Sawdust is easy to apply, weed free, and decomposes slowly. Generally, sawdust should be allowed to age or weather for a year before being applied. If fresh sawdust if used, make sure the sawdust doesn't cake. Do not use sawdust from treated lumber in the yard and garden.

Wood chips are an excellent mulching material which may be available from local arborists. The material is obtained by passing tree and shrub trimmings through a mechanical chipper. Municipal or private yard waste sites are other possible sources of wood chips. They are generally used in landscape plantings, such as around trees and shrubs and in perennial beds.

Commercially packaged bark mulches are available shredded or as chips, nuggets, or chunks. They are sometimes available in bulk quantities from nurseries and landscape companies. Bark mulches are attractive, weed free, and decompose slowly. Bark mulches are best used around trees and shrubs and in perennial beds.

Sawdust, wood chips, and bark mulches can be safely used around the home. These materials will not "attract" termites to the house.

Sawdust, wood chips, bark, and ground corncobs may deplete nitrogen in the soil during the process of decomposition. The bacteria in the soil that gradually break down the organic materials require large quantities of nitrogen. Since the woody materials contain only small amounts of nitrogen, the bacteria may utilize some of the available nitrogen in the soil. A possible nitrogen deficiency can be prevented by sprinkling a small amount of complete fertilizer, such as 5-10-5, on the soil surface prior to applying the mulch. Thereby providing sufficient amounts of nitrogen to meet the needs of both the bacteria and plants.

The type of mulch determines the depth of the material. Apply most organic mulches 2 to 4 inches in depth. The selection of the mulch should be based on availability, cost, appearance, function, durability, and other factors.



This article originally appeared in the June 30, 1995 issue, pp. 1995 issue, pp. 99-100.

Year of Publication: 
1995
Issue: 
IC-470(17) -- June 30, 1995