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YARD AND GARDEN

Mulch ado about something

Dave Robson

Summer's heat really stresses plants. High temperatures and humidity may cause plants to wilt, losing water through the leaves faster than roots can replace it. Wilting isn't serious as long as the soil has water. Only when the soil water supply is low does wilting become serious. The result is that plants may not recover.

Of course, maintaining an adequate supply of moisture in the ground is the key— too little and the plants wilt beyond recovery, too much and the roots rot and plants wilt, also.

Mulches are a means of limiting evaporation from the soil. Covering the soil with a mulch provides a layer that water needs to penetrate before being absorbed by the air. An added benefit is that mulches keep soils cool, allowing more root growth and activity. It's more difficult for sun's radiation to penetrate into the soil to warm it.

Mulches can be divided into two different groups—organics and synthetics. Each has its own advantages and disadvantages.

Organic mulches are derived from plant materials. Organic mulches tend to look more natural in the landscape and call less attention to themselves. Organic mulches enrich the soil as they decompose. Common mulches include wood, leaves, straw, compost and grass clippings. Wood can be subdivided into hardwood chips, shredded bark, pine bark, sawdust, and cypress mulch.

Wood mulches have a strong advantage of being long-lived. They don't break down as fast, nor do they blow or wash away. Wood pieces come in various sizes and colors. Shredded bark breaks down the fastest of all types of bark; cypress is probably the longest lived, though the most expensive. Pine bark falls in the middle.

Wood mulches also include sawdust, which should be used with caution. Sawdust breaks down quickly and ties up available nitrogen in the soil. Plants can temporarily turn yellow and appear stressed. If sawdust is used, consider scattering an extra handful of garden fertilizer over the material.

Walnut sawdust and wood chips can contain compounds that stunt the growth or kill plants outright. It is recommended that walnut products be used sparingly.

Avoid using chips or bark from trees that have suddenly died. It is possible that fungi, bacteria or other pathogens might infect other plants. Materials from these trees can be composted for a year or more before using to help destroy any potential disease organism.

Barks can grow several slime molds on the surface, creating foul odors. Make sure to rake and fluff mulches at least twice a year to minimize this problem.

Composted leaves make an excellent organic mulch. Shredded leaves that are partially decayed look natural, help prevent water evaporation and don't tie up soil nutrients. To prevent leaves from matting or blowing away, it's helpful to make sure they are partially decomposed.

Grass clippings are used by some as a mulch. Clippings are high in nitrogen and can produce an ammonia smell if piled too deeply. Grass also generates heat as it breaks down which can either warm up the soil and reduce root growth, or warm plants causing them to use more water. It's better to allow clippings to dry and partially decompose before applying.

Pine straw is one of the newest rages in mulches. Essentially, pine straw is nothing more than baled pine needles that may contain some limbs and cones. Pine straw doesn't break down fast, doesn't tie up nutrients and tends to discourage insects. It is more difficult to apply and can create a fire hazard if it dries out. Some people are concerned about the ecological effect of harvesting the fallen pine needles from forests.

Straw can be used, provided it is free of

David Robson is an Extension Educator, Horticulture, at the Springfield Extension Center, Cooperative Extension Service, University of Illinois. You can write to Robson in care of Illinois Country Living, P.O. Box 3787, Springfield, IL 62708. Telephone: 217-782-6515. E-Mail: robsond@idea.ag.uiuc.edu

ILLINOIS COUNTRY LIVING • AUGUST 1996

weed seeds. Wheat straw tends to be cleaner than oat straw. Straw doesn't have quite as natural an appearance in the landscape as other materials. However, the availability and cheapness may be a factor.

Compost doesn't have to be incorporated into the soil; it makes a great mulch on top. The material can then be tilled in during the fall or early next spring. Make sure you have a well blended compost mix before applying.

Cocoa bean hulls are a by-product of the chocolate industry. Hulls are dark in color and have a faint chocolate aroma. They will grow mold if applied too heavily.

Rice hulls are another new product on the market that appear to have great potential as a garden mulch. Again, the material is a by-product.

Most organic mulches should be applied in layers no deeper than 3 to 4 inches. Sawdust and cocoa bean hulls should be less than an inch. Mulches should be kept away from the trunks of trees or shrubs to avoid rotting and attracting rodents to feed on the plant. Additional mulch can be added yearly to improve the appearance or maintain a proper height layer.

Make sure the soil is moist before applying an organic mulch. Remember, it may take more watering to wet the soil during a dry spell as the water has to penetrate the mulch.

Inorganic mulches are usually rocks or plastic. They don't break down as fast and usually are relatively inexpensive to apply. It is harder to dig through them to plant, but longevity may make up for that fact.

Plastics aren't used too much as they prevent water and air exchange. Plastic is helpful in keeping down weeds, though. Its inability to "breathe" can keep wet soils wet and dry soils dry. Poking holes in the plastic only allows weeds a foothold to become established.

Barrier mats allow for water and air penetration, but need another type of mulch on top to hold it in place.

River rock, pea gravel and merrimac are three natural looking rocks that fit into the landscape without calling attention to themselves. Rocks of these grays and brown work best when several sizes are used in the landscape. Rock should be applied as deep as bark mulches.

Avoid white limestone and marble chips. If I had my choice, they wouldn't be offered. These materials are cheap, but they can raise the soil pH, tying up nutrients and wreaking havoc with acid loving plants such as evergreens and oaks. These materials are also "white" and draw attention to themselves in the landscape.

AUGUST 1996 • ILLINOIS COUNTRY LIVING 19