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IN THE GARDEN; Seaweed to Wood Chips, Mulch Is a Plus

By JOAN LEE FAUST

Published: Sunday, May 17, 1998

http://www.nytimes.com/1998/05/17/nyregion/in-the-garden-seaweed-to-wood-chips-mulch-is-a-plus.html

MULCHES may invite giggles, but they are a necessity nonetheless. The most obvious plus about mulches: when the ground is properly covered with an organic material of some type, weeds do not have an easy time growing. Also, the soil remains cool and moist and the garden looks as though someone cares.

The biggest question that most people have about mulches is what to use. The answer is it depends on where you live and what is available. In the Northeast, wood chips, bagged and sold by the bulk, are one of the first choices because they are inexpensive and available. Also, they look great. Sometimes gardeners acquire their own supply of wood chips from local tree surgeons who are often glad to dump some chippings on the property. If mulch material has to be purchased, visit garden centers and nurseries to learn what is available.

Those who live along the shore like to use seaweed that washes up. Or there are the readily available piles of last fall's leaves, which are excellent as far as the garden soil is concerned. If these are fed into a mechanical chipper and chopped into small bits, they decompose rapidly and do wonders for the soil. Besides, they, too, look great.

Caution, however, on digging in and applying piles of unchipped leaves. This vegetable matter needs a long time to decompose if not chipped up -- sometimes the leaves mat or never do rot down properly -- and plant roots have quite a struggle working around them.

Of course, compost is a great sort of mulch, but it is best relegated to life as a dig-in soil improver at planting time rather than an over-the-ground type of mulch.

Also note: peat moss should not be used on top of the soil. It does look attractive for a time. But peat moss acts like a blotter and usurps soil moisture from the ground after it is applied. If the season proves dry, the peat moss dries, too, and blows all over the property and can be a great nuisance. If peat moss must be used, work it into the soil, never on top.

Another thought about purchasing mulches. Cocoa hulls, buckwheat hulls and the like are handsome, airy and effective. These are often used by rose gardeners as they provide an attractive soil covering and do keep down the weeds. But for a large expanse of mulch material, they can be quite expensive.

How deep? To be effective, a good mulch layer should be about three to four inches deep. This size layer will not smother the earth beneath but will be deep enough to help snuff out weeds and keep the ground moist and cool. And the mulch covering slows the evaporation of soil moisture.

Anything deeper than those several inches is not needed nor is it wise. Too deep a mulch would cut off air circulation needed by the soil.

What about nitrogen depletion? This question often occurs when the topic of mulches is considered. The argument is that the microbes needed to break down, say, a wood chip mulch usurp vital nitrogen from the soil and therefore deprive plant roots of this much-needed nutrient. Researchers, however, believe this is not an issue because the mulch layer is not mixed in with the soil. Wood chips do eventually weather on their own and incorporate into the soil's texture. And replacement in a few years is the usual rule.

Those who remain concerned about the use of wood chips, can solve the problem easily. Compost them for a few months before use just to be sure.

The composting rule would also be important for the use of any animal manures as mulch or soil additives. Many times stable mixtures of manures with bedding straw are used as an excellent mulch for shrubbery plantings and around trees. But composting first for several months is recommended.

Caution as well on the use of grass clippings. Alone, they dry and blow about and make an ugly mess. Also, if are piled too high, they become odorous and block out any air to the soil and plants. Again, compost grass clippings or mix them well with other organic materials before use as mulch.

Finally, when piling mulch, do be careful using it around trees, especially young trees that have just been planted. Too many times, untrained planters pile huge amounts of wood chips around the bases of young trees and shrubs. The mounds may look great, for a time, but they can snuff out air, keeping the young bark damp, which invites insects and rodents to feed or nest or both. In a few years time, the woody plants succumb.

Mulches can be fine to keep the bases of trees out of harm's way especially when mowers or weed whackers are in use, but keep the mulch at least six inches away from the base of the tree trunk and pile it thinly so that the natural aeration is not snuffed out.

When used properly and artfully, mulches go a long way toward good gardening. They are not work enders, but they certainly do help to cut down on many of the hours spent keeping things under control.