Make the Most of Your Mulch
Greentips: July 2003
Did you neglect to mulch your garden this spring? It's not too late to reap the benefits of this protective soil covering for plants, trees, and shrubs. Mulch not only beautifies your garden, it also reduces weeds, conserves soil moisture, and controls erosion and temperature. Some mulch can even enrich your soil.
There are many varieties of mulch, both organic and inorganic. Organic mulches are made from wood products (such as bark, chips, shavings, and sawdust), pine needles, buckwheat or cocoa hulls, grass, straw, crushed corncobs, leaves, and newspaper. There are also "living mulches" such as clover and other ground cover grown between your plants. Inorganic mulches include rocks and gravel, aluminum foil, black plastic, and geotextiles (woven fabrics made from polyester or polypropylene).
Organic mulches are generally preferred because they can improve the soil, though they have their drawbacks. Some contain weed seed, are flammable, or provide homes for rodents, but these problems can be avoided or mitigated. Of the inorganic mulches, rock and gravel are the most attractive, but only in certain landscapes. Plastic is not recommended because it can cause polluted runoff.
In choosing between the various options, the most important considerations are:
pH—Some mulches are more acidic than others and may harm your plants. Match the pH to your plants' needs.
Water penetration—All mulches conserve moisture already in the soil, but some (such as wood chips, pine needles, or stone) let new water penetrate better than others. Plastic keeps water out altogether, so poke holes in it to let water drain through.
Insulation—For your summer garden, choose mulch that keeps heat out (hay, wood shavings, or compost) but apply it after the ground has warmed from the spring. During the winter, apply heat-trapping mulch (pine needles or straw) after the soil freezes. Bark, wood chips, and stone can be used year-round for trees and shrubs.
Soil improvement—Organic mulches fertilize the soil as they decay, though not all at the same rate. In general, mulches that decay slowly (such as bark or straw) are appropriate for trees and bushes, and mulches that break down rapidly (such as shredded leaves or grass clippings) are better for annuals. If soil improvement is important, choose mulch that decays rapidly or is rich in nitrogen, a valuable soil nutrient.
Appearance—Mulches have varying aesthetic appeal and can substantially affect the way your garden looks and smells. Factor color, texture, tidiness, and aroma into your choice.
Application and maintenance—Is convenience important to you? Then look for mulches that are easy to apply and maintenance-free.
Expense—As always, your budget is a consideration. Mulch prices range from free (grass clippings and leaves) to expensive (processed buckwheat or cocoa hulls).
No single mulch is perfect for every individual and garden. You may even find you want to use different types in different parts of your yard.
To figure out how much mulch you'll need, calculate the surface area to be covered and purchase enough for a layer two to four inches thick. Smell the mulch before using it; if you detect vinegar, ammonia, or sulfur, it has turned "sour" (toxic) and can harm your plants.
Before applying mulch, clear the area of weeds. Spread mulch evenly, leaving at least six inches free around tree trunks and plant stems. Maintain the proper depth throughout the growing season, adding more when necessary, but don't overdo it. Too much mulch can lead to excess moisture and root rot.
