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Mulch: 1988 garden hero.

It will save you water and make your plants grow better You need only to decide which kind

Drought or not, keeping a layer of mulch over the soil that plants grow in is-in most situations-simply good gardening. But today, as much of the West faces the reality of enforced water conservation, mulching becomes a flat-out necessity. Hear these four experienced gardeners:

Dick Wolf Thousand Oaks, California: "Mulch makes my pocketbook sing. My water bill is a third of what it used to be." Bryce Martin, San Ga"I wouldn't consider growing roses without a 3- to 4inch mulch. Without it, I'd be watering every day instead of twice a week."

Dick Hildreth, State Arboretum of Utah: "All our gardens are mulched. We use less water, less often. Mulches also look good, save labor, cut down on weeds."

Dorothy Booher, Curtin, Oregon: "We grow everything from asparagus to strawberries, and all our crops are mulched. Mulch means less work and healthier, more pest-free plants."

What mulch is . . . and what it does

Here we deal only with organic or natural-material mulches. Any of those listed here can be rotary-tilled into the soil in fall to decompose over the winter and improve soil. (Plastic, gravel, and other inert materials are effective mulches in some uses, but they present totally different advantages and disadvantages.)

A mulch is any material placed over the soil to reduce evaporation, to reduce or prevent weed growth, and to insulate it from extreme temperature changes.

Water leaves the soil by way of plant roots and by evaporation. A mulch limits that evaporation. Potential savings are greatest in hot, dry climates.

Weeds take water from the soil, and mulches prevent weeds. They do that mostly by covering the weed seeds and shading any seedlings. Since weeds compete with your desirable plants for water, reducing their numbers is an important conservation step.

Mulches keep the upper inches of the soil cooler in daytime, warmer at night. They also prevent mud from splashing onto leaves, protect falling fruit from injury, and make a garden bed look tidy.

A mulch can even encourage worms. Good soil and earthworms are always associated, but which comes first? To thrive, earthworms require an abundant supply of organic matter and moisture. They seem to disappear in soil that is dry, cold, or wet. But the typical generously mulched garden is also generously populated by earthworms.

To conserve water, the most important time to mulch is late spring, once soil is warm. The most important place to put mulch is over the plants' drip zone.

How much organic mulch to use?

What kinds can you choose from?

An effective layer of water-saving mulch is thick enough to ensure dead airspace. Generally, this calls for a 1- to 2-inchthick layer of mostly 1/2-inch particles. Apply larger particles in thicker layers. One cubic yard (27 cubic feet) of mulch covers 108 square feet with a layer about 3 inches deep. Three cubic yards cover 1,000 square feet 1 inch deep. A 2-cubic-foot bag covers 8 square feet 3 inches deep. A 5.6-cubic-foot bale of compressed peat moss will expand to cover about 40 square feet 2 to 3 inches deep. Three categories of organic mulches are available to home gardeners:

Composted mulches are any of the many commonly available materials derived from plant or animal material. Eventually, when they decompose, they benefit soil by improving its structure and preventing crusting. In addition, some have minor nutrient value.

Partially composted materials such as manure and mushroom compost are not recommended for use as summer mulches. These usually have a high level of salts, which can damage plants. Apply them in fall so that winter rains can wash out the salts before spring.

Noncomposted mulches-fresh sawdust or shavings-offer the same benefits as other organic ones. But as they decompose in or adjacent to soil, these products will out-compete plant roots for their most important nutrient nitrogen. For this reason, these materials don't make good summer mulches, either.

To safely use noncomposted or fresh sawdust or shavings mulches and prevent nitrogen deficiency, apply 3 pounds of actual nitrogen per cubic yard of material. Use slow-release nitrogen fertilizers, such as ureaform (38-0-0).

What are the drawbacks?

The worst that can be said of some organic mulches is that they encourage such nuisances as earwigs, sowbugs, slugs, and snails by creating a dark, moist, cool environment. Coarse-textured organic materials offer the most hiding places.

A word about sludge compost

Recycling municipal sewage sludge in home gardens is an ingenious use of a nutrient-rich but otherwise useless material. As cities grow and places of disposal diminish, recycling sludge becomes increasingly important.

A deserved criticism of sludge compost concerns its content of heavy metals, especially cadmium, that plants can absorb.

Sunset hired an independent laboratory to test sludge composts from Seattle, the Bay Area, and Los Angeles for cadmium. The highest level we found, 8.2 parts per million, was in Los Angeles. The Seattle sample tested lowest, at 2.5ppm; the Bay

Area's showed 4.9ppm.

But a manual published by the California Department of Health Services in 1983 states that up to 50ppm cadmium in sludge compost is acceptable.

In 1979, the USDA published Use of Sewage Sludge Compost for Soil Improvement and Plant Growth. For a free copy, write to Agricultural Research (Northwestern Region), Science and Education Administration, USDA, Beltsville, Md. 20705. In 1980, the EPA published Cadmium.- Health and Environmental Effects ($2.10); write to EPA, RCRA Information Ctr., Office of Solid Waste, Washington, D.C. 20460.

We tested the mulches with moisture sensors and soil thermometers

Last May, UC Cooperative Extension and Sunset tested mulches at UC's South Coast Field Station at Irvine. In a 10-day test, we compared moisture savings and soil temperature reductions with three mulches -peat moss, commercial compost, and shredded fir bark-at depths of 1, 2, and 4 inches, Japanese privet

was the test plant.

Moisture sensors and thermometers tracked the differences. On the second day, the plant with no mulch at all showed most moisture stress; the plant with 4 inches of fir bark around it showed the least. On the last day (after two days of temperatures near 100[degrees]) the plants in best shape were those with 2 or 4 inches of fir bark or 4 inches of commercial compost.

Temperatures an inch below soil line under all the mulches averaged 10[degrees] cooler than in unmulched soil.

16 widely available mulches: pros and cons, cost, advice on use

These are free, if you have them, make them, or can find them

Homemade compost is the stuff you make yourself from garden or kitchen leftovers. It usually has some nutrient value, but might include weed seeds.

Before you spread it, sift to remove all large, uncomposted pieces.

Lawn clippings make excellent mulch if your lawn is free of weeds such as crabgrass and Bermuda grass. Let the clippings dry a day or so in thin layers on pavement or plastic before using as mulch-or they will cake and breed flies.

Pine needies are there for the collecting under any pine tree. Put on a layer 6 inches deep, or even deeper, under and around acid-loving plants.

Chipper debris is often free for the asking (and hauling) from city or private tree crews. Check the telephone book white pages for municipal arborist, yellow pages for private tree service companies.

Although variable, it's generally long lasting. Avoid eucalyptus chips; they might retard plant growth.

Apply it in layers at least 2 inches deep around trees and ornamentals. In spring, add half the amount of nitrogen recommended for sawdust.

Some cheapies-especially if you can buy in bulk

Cotton gin waste, available in California's San Joaquin Valley for a penny a pound, comes in bulk only. A good additive to a compost pile, it's rich in nutrients.

Apply it an inch deep, or shallower. Because it's extremely light, you should cover it with another, denser mulch, or lightly cultivate it into the soil. If it seems to repel water, use a wetting agent. Don't use it under olive trees; it can carry a disease that they get.

Nut hulls are cheap; if you live in a nutgrowing area, they're usually available for about $10 a cubic yard. Look for pecan hulls in Visalia, California; Green Valley, Arizona; or Las Cruces, New Mexico. Pistachios are abundant near Chico, California. Almond and walnut hulls are sold throughout California's Central Valley.

Apply the hulls 2 to 3 inches deep. Such a mulch lasts up to two years. Pecan hulls don't float away-and they have an attractive red coloring.

Rice hulls, sold in the Sacramento area, cost about $2 per 4-cubic-foot bag or $7 to $12 for a pickup load (approximately 6 cents per square foot, 2 inches deep). Cushiony and absorbent, they're an ingredient in many commercial mixes.

Apply the hulls 2 to 4 inches deep. If you don't want them to blow around, cover with a thin layer of heavier mulch.

Straw and hay are sold at feed stores: hay for about $9 a bale, straw for $5. Pull off layers about 4 inches thick and set them out around plants or between rows without breaking them apart.

Straw has an advantage in that it contains very little seed; hay contains much-and that seed germinates into weeds. When hay's seed germinates, you can turn the layers over to get rid of emerging plants.

More expensive choices-around $1 to $2 or more per cubic foot

Aged sawdust isn't necessarily aged; sometimes it's only a matter of a few days old. An excellent material to add to your own compost, it costs $3 per 3-cubic-foot bag or around $20 per cubic yard (about 12 cents per square foot, 2 inches deep). In late spring and in midsummer, apply 1to 2-inch layers around ornamentals. But use with caution near vegetables and fastgrowing plants; it might steal nitrogen.

Douglas fir bark is available in graded sizes: best for mulch is the grade called "beauty bark," With 3/4- to 1-inch particles. At about $2.50 per 2-cubic-foot bag, or $10 per cubic yard (6 cents per square foot for a 2-inch layer), it's most common in western Oregon and Washington.

Apply it 2 to 3 inches deep.

Hemlock bark is a richer brown than other barks, and the color lasts longer. It also lacks the hard fibers (the ones responsible for splinters in fingers) that the others contain. It's sold only where hemlock grows; most places charge $3 per 2cubic-foot bag, $14 per cubic yard (8-1/2 cents per square foot for a 2-inch layer).

Apply it 2 to 3 inches deep.

Decorative bark is mostly white fir or pine, chiefly from Arizona and South Carolina. Sizes are graded: 1/4- to 3/4-inch bark is usually called pea, 3/4- to I 1/2-inch is acorn, 1-1/2- to 2-1/2-inch is jumbo. It ranges widely in price: $1 to $3 per cubic foot in bags, $5 to $20 a yard in bulk. A rough average cost for a 2-inch layer, delivered in bulk, would be about 12 cents per square foot.

For an effective water-saving mulch, you need to spread coarse bark chips in a thicker layer than you would other materials 3 to 6 inches. Small chips tend to scatter; larger ones are more wind resistant but can float away. All turn gray with age.

Shredded bark-sometimes called walkon bark--is available throughout the West. It looks natural and is slow to decompose; the irregular pieces hold well on slopes and in windy areas. It costs $7 for a 3-cubic-foot bag; in bulk, about $30 a cubic yard (18 cents per square foot, 2 inches deep). Use it in 2-inch layers.

Aged redwood sawdust costs $6 per 3cubic-foot bag; in bulk it runs about $24 a cubic yard or 15 cents per square foot, 2 inches deep. In late spring, apply it in 1to 2-inch layers around vegetables or ornamentals.

It is not composted, and it's slow to decompose. When you apply it, add half the amount of nitrogen fertilizer recommended for fresh sawdust.

Costlier: commercial compost and peat moss

Commercial compost typically consists of sludge mixed with wood by-products. It has some nutrient value-it contains around 2 percent nitrogen-and can hold 100 percent of its own weight in water. Expect to pay $4 to $5 per 2-cubic-foot bag; $30 per cubic yard, or 18 cents per square foot, 2 inches deep.

Apply a 1-inch deep layer around vegetables or ornamentals. Roses and similar heavy-feeding plants benefit from deeper layers. For more information, see A word about sludge compost (at right).

Peat moss seems more expensive than it is, since it's compressed. When you open the bales, it expands about 1-1/2 times. Spread peat moss 2 to 4 inches deep. Use the coarse grade if possible; it's more wind resistant. It's acidic and holds moisture very well, but when thoroughly dry it repels water and can blow away; use a wetting agent to rewet it.

You'll pay about $15 for a 5.6-cubic-foot compressed bale, or about 30 cents per square foot when spread 2 inches deep. It's not sold in loose bulk.
COPYRIGHT 1988 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1988 Gale, Cengage Learning. All rights reserved.

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Date:Aug 1, 1988
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