Mulches are commonly used to enhance the beauty of landscapes, suppress weeds, conserve soil moisture and buffer plants from the damaging effects of traffic and lawn equipment. Organic mulches also can improve the soil structure and increase the fertility of landscape soils, which often are compacted and lacking in organic matter, especially around newly constructed buildings. Horticulture specialists with Iowa State University Extension and Outreach answer mulch questions this week. To have additional gardening questions answered, contact the specialists by calling or emailing the ISU Extension and Outreach horticulture hotline at 515-294-3108 or firstname.lastname@example.org.
Organic mulches serve several important functions in gardens and landscape plantings. Mulches help control annual weeds and conserve soil moisture. They reduce soil erosion by reducing the impact of raindrops and water runoff. Mulches can help reduce the severity of some diseases, such as blights on tomatoes. They help keep fruits, vegetables and flowers free of rain spattered soil. They also reduce fruit and vegetable spoilage. Organic mulches moderate soil temperatures. During the hot summer months, they help maintain cooler soil temperatures. Mulches also provide an attractive background for landscape plantings.
Lawn clippings, straw and leaves are excellent mulches for the vegetable garden. Allow lawn clippings to dry before applying them to gardens. A thick layer of fresh lawn clippings may get hot and produce an unpleasant odor. If the lawn has been treated with a broadleaf herbicide, don’t use the clippings until the lawn has been mowed two or three times after the application. Straw should be free of crop and weed seed. Suitable materials include wheat, oat and soybean straw. Leaves should be shredded or composted before applied as mulch. Shredded or composted leaves are less likely to blow away in the wind. A mulch depth of 2 to 4 inches would be appropriate when applying these materials to the vegetable garden.
Yes, shredded newspapers or whole sheets may be used as mulch in the vegetable garden. Newspapers use organic inks so gardeners need not worry about lead contamination. When using newspaper sheets, place a layer of two or three sheets between plant rows in the garden. Water the sheets so they stick to one another and to the soil surface, then place a layer of dry grass clippings, shredded leaves or straw over the newspaper.
Suitable mulching materials for a raspberry planting include straw, shredded leaves, lawn clippings, crushed corncobs, sawdust and wood chips. The depth of the mulch needed depends upon the material. The depth ranges from 3 to 4 inches for fine materials, such as sawdust, to 8 to 10 inches for straw. Since mulches gradually decompose, apply additional material each year. Avoid mulching poorly drained soils to discourage root diseases.
Excellent mulching materials for perennial beds and borders are shredded bark and wood chips. These materials are widely available, attractive and long-lasting. Other possible mulches include shredded leaves, dry grass clippings and pine needles. Place 2 to 3 inches of mulch around the perennials. However, do not place the material directly over the plant crowns.