Organic Mulch Materials

By The Old House Web

Organic Mulch Materials

Grass Clippings

Grass clippings are readily available when the lawn is actively growing. Using grass clippings has several disadvantages, however. Weeds from the lawn can be introduced into the mulched bed. If the clippings are applied too deeply and packed too tightly they will release heat and a foul odor as they decay. Clippings from lawns that have been treated with weedkillers can cause herbicide injury in tender plants.


Leafmold can be made by composting leaves in the fall. The material should be partially decomposed by the following spring. It is a good mulch but difficult to apply evenly and may not be particularly neat looking. Leafmold collected from wooded areas may contain nematodes.


Leaves, probably the most inexpensive material available, are used extensively in areas with many trees. Avoid leaves collected from streets that have been sprayed with oil or treated with calcium chloride--both oil and calcium chloride are toxic to plants. Leaves may be difficult to keep in place in windy locations. Very dry leaves can be a fire hazard, and packed, wet leaves interfere with air and water movement into the soil. Leaves should be mixed with some other light material, such as straw, to prevent their becoming a compacted, soggy mass.


Peat is often called "peat moss" but this is a misnomer. Moss peat comes from mosses, while other types of peat originate from cattails, reeds, sedges and other similar water plants. Sphagnum peat moss is acid and useful for mulching and amending the soil around azaleas, rhododendrons and other plants that grow best in acid soil. For other plants, apply limestone at 3 to 5 pounds per 100 square feet on top of a 2-inch Sphagnum peat mulch counteract the acidity. Sphagnum peat is very resistant to decomposition and has many fibers into which roots often grow profusely. Hypnum peat is usually neutral or slightly alkaline, breaks down more rapidly and may have few fibers.

Most types of peat are brown and serve as a neutral background in the landscape. If the surface of a peat mulch becomes very dry, it will shed water and require stirring. Carelessly tossed cigarettes can ignite peat, but it smolders rather than flames. Fine peat will often be blown away in windy weather, but chunky peat will hold. Self- seeding of some plants may occur in peat.

Pine Boughs or Needles

These are usually recommended for winter protection of newly set or somewhat tender ornamental plants but can serve as a mulch as well. Any needle-type evergreen is a satisfactory source.


Sawdust is very commonly used in areas where it is readily available. Nitrogen deficiency is almost certain if fertilizer is not applied regularly. The alleged toxicity of sawdust is usually nitrogen deficiency in the soil from the action of micro-organisms decomposing the material. Sawdust from walnut logs can stunt plants because of toxic materials in it.

Bark--Shredded, Chunked or Chipped

Bark has become popular in recent years. It makes an excellent mulch and is very attractive in landscape plantings. Shredded, chunked or chipped bark lasts as long or somewhat longer than peat moss and adds organic matter to the soil. Bark may also be used for walks or paths in the garden area. To prevent nitrogen deficiency in plants mulched with bark, apply nitrogen fertilizer.


Straw is used for winter protection and as a summer mulch. It is highly flammable, so do not use it where cigarettes or matches could be carelessly flipped into the material. Additional nitrogen must be applied to prevent starvation of the mulched plants. Weed seeds may be introduced with this mulch. Unless the straw is chopped into short lengths, it will be difficult to apply between plants growing close together.

Wood Chips And Shavings

Wood chips and shavings have become available in large quantities from utility companies. These materials vary in coarseness. They are sometimes rather fine or may be largely broken twigs or branches. Wood chips decompose slowly and may cause nitrogen deficiency if additional fertilizer is not applied. They make a very rustic-looking, satisfactory mulch. Wood chips should not be used in foundation plantings next to the house where termites are or could be a problem.

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