BU-03296     Revised 2000

To Order

Composting and Mulching: A Guide to Managing Organic Yard Wastes

« Previous Section | Table of Contents | Next Section »

Use of Compost in Potting Soils

Leaf compost can be used as a component of potting mixes. Generally, no more than one-quarter to one-third by volume of the potting mix should be compost, because over time some of the compost is likely to decompose and the volume of the potting soil will be reduced. In addition, high levels of compost in a potting mix may cause waterlogging and poor aeration for roots.

Although proper composting destroys most weed seeds and disease organisms, some may still survive due to incomplete mixing. To obtain a completely pasteurized leaf compost, it is necessary to heat the material in an oven until the temperature of all the material reaches 160 degrees F and is maintained for 30 minutes or longer. Pasteurization will also kill beneficial organisms in compost, some of which help to suppress certain soilborne diseases. So if your compost doesn't have many weed seeds or disease organisms, there may be an advantage to using it unpasteurized fresh.

Use of Compost as a Mulch

Mulches are used in gardens to suppress weeds, conserve soil moisture, reduce soil erosion, and modify the soil temperature (makes it cooler in the summer, reduces rapid decline and fluctuation in the winter). Yard waste compost makes an ideal mulch for annual and perennial gardens. All you need to do is apply a 2-4 inch layer of compost around the base of the plant. Periodically throughout the summer, you may need to add more compost over the old layers to maintain the benefits of the mulch. The soil environment beneath the mulch is favorable for earthworms, which are valuable for aerating the soil. Organic matter is gradually added to the soil as the mulch decomposes.

For annual gardens, the mulch can be worked into the soil at the end of the season to further improve the soil. For perennials, it may be beneficial to remove the mulch in the spring to allow the soil to thaw out faster. As discussed above, well-decomposed yard waste compost will not tie up nitrogen. Therefore, it is not necessary to add nitrogen beyond that recommended for plant growth. If noncomposted or partially composted leaves are used, one tablespoon of a high nitrogen fertilizer (for example, 27-3-3) should be applied to each five-gallon bucket of mulch.

Alternatives to Composting

When proper lawn management is used, there is no need to collect grass clippings⁸. As long as the grass is not excessively long and clippings do not thickly cover the lawn surface after mowing, there is normally no need to collect the clippings. Aside from reducing the work involved in lawn maintenance, leaving the grass clippings benefits the turf by returning nutrients and organic matter to the soil. If evenly distributed, clippings left on the lawn can be equivalent to one fertilizer application per year.

To keep your lawn looking healthy and control the amount of clippings generated, several maintenance practices should be followed. It is important that mowing height be properly adjusted. The best cutting height depends on the turfgrass varieties present in the lawn and whether the lawn is in sun, full shade, or a combination of both. Lawns in full sun have the greatest potential for quick recovery after mowing and can therefore be cut shorter. Those in the shade need all the available leaf surface possible for photosynthesis. Thus, grass in the shade should be cut slightly higher than grass in the sun. Where both conditions are present, an intermediate height is recommended. Some suggested mowing heights for home lawns are listed below.

Fine Fescue	2 to 3 inches
Kentucky bluegrass/perennial ryegrass	1-½ to 2-½ inches

Kentucky bluegrass:
Improved varieties	1 to 2 inches
Common types	1-½ to 2-½ inches
Kentucky bluegrass/red fescue	2 to 3 inches

Mowing frequency also directly affects the amount of clippings generated. How often to mow depends on the cutting height selected and how fast the grass grows rather than on specific time intervals such as once per week, etc. Ideally, no more than one-third of the leaf surface area should be cut at any one time and the clippings should be no longer than one inch. As an example, a lawn with grass three inches tall should be cut to about two inches. Excessive defoliation in a single mowing can make the lawn more prone to stress and disease problems.

Be careful not to overfertilize your lawn. Overfertilization (primarily with nitrogen) will cause excessive growth and, unless the lawn is cut more frequently, the clippings will be slow to reach the soil and decompose. Reducing excessive thatch levels through lawn renovation will improve infiltration of the grass clippings down to the soil surface. It is best to mow your lawn when it is dry so clippings will be able to filter down to the soil without clumping.

Two types of mowers available to homeowners are reel and rotary. Either will do an acceptable job when sharpened and adjusted properly. Mower blades should always be kept sharp, as dull blades can result in deterioration of the lawn area. Rotary mowers are now available with a mulcher attachment for the blade. Mulchers reduce the size of the clippings left behind and should result in faster decomposition of the grass blades. However, if you are mowing on a regular basis and not removing more than one-third of the grass blades at a time, additional size reduction is not necessary.

If grass growth is excessive you may need to remove the clippings. Lawn clippings can be used in the compost pile as described above or they can be used as a mulch in the garden. If used as a mulch, care should be taken not to over-apply fresh clippings as they tend to inhibit moisture and oxygen penetration into the soil, and may produce offensive odors. Mixing fresh clippings with compost provides an excellent mulching material. Do not use grass clippings as a mulch if the lawn has recently been treated with herbicides. Where herbicides have been applied, it is recommended that the clippings be left on the lawn for at least three mowings. For more information on lawn fertilization and lawn care, contact your local county Extension office.

« Previous Section | Table of Contents | Next Section »

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.