Choosing the right type of mulch depends on the job at hand

Contributing Garden WriterSeptember 21, 2012 

From crushed rock to chunky bark bits, newspapers and rolls of plastic, various mulch materials will have you and your garden covered for better growing.

You can use mulches to blanket all sorts of plantings for various purposes, so when choosing mulch, think first about what you want to accomplish.

Applied to summer vegetable and perennial flower gardens, mulch prevents weeds from sprouting between plants and conserves soil moisture. In fall and winter, it protects tender roots from frost damage. Year-round, decorative mulch placed under trees and shrubs, and alongside walks and driveways adds a tidy look to landscapes.

Here are a few mulch types:

Plastic film and landscape fabric: In a vegetable plot, opaque plastic film laid between rows works well to block weed growth, help warm soil early in the spring and conserve soil moisture. Drip irrigation lines below the plastic are needed to provide moisture. New, more permeable mesh landscape cloth types allow rainfall or above-ground irrigation to pass through and can be combined effectively with some of the organic mulches listed below.

Newspaper, straw, leaves and compost: These biodegradable materials are great organic vegetable garden mulches and can keep soil cooler under the hot summer sun, block light, and prevent weeds in summer and winter.

Compost, which you can cure at home by recycling your vegetable waste, yard clippings and plant materials, is invaluable in returning nutrients to the soil and improving its structure.

In cold weather, a covering of wheat straw is recommended to help strawberry plants overwinter, as they are particularly susceptible to damage from frost heaving as soil shifts between freezing and thawing.

Pine straw, sold in small bales of long pine needles, is another attractive insulator for use around perennials. It does not compact easily and allows plentiful air and moisture flow. Because it helps acidify soil over time, it is especially helpful around tender, acidic-soil-loving plants such as azaleas and rhododendrons.

You also may reuse and recycle low-cost organic mulch materials such as leaves and paper. Chop up yard leaves by running a mower through a shallow pile. Some cautions: Be sure that water can permeate through layers of this sort of mulch, and take care that they are weighted down enough so the wind can't blow them away. Do not use walnut leaves as mulch, because they contain compounds that inhibit growth in some plants, such as tomatoes and peppers.

Bark nuggets and chipped or shredded wood: These organic mulches, which decompose over time, are useful as decorative elements around landscape plantings such as established trees and shrubs and as soft padding for garden paths. Mowing is much easier if you don't have to reach under branches and over shallow roots. Water and air can move through them, yet at the same time they suppress weed growth.

Be careful to use well- composted and aged wood chips, and avoid piling the mulch directly against the plants' trunks. "Mulch volcanoes," as they're called, not only encourage formation of side roots that weaken the trunk's structure but allow disease and insect infestations to take hold more easily through direct contact.

Maintenance considerations include breaking up the mulch if a water-resistant barrier forms, and adding a fresh layer of mulch every couple of years as older material decomposes.

Because wood chips use a lot of nitrogen, they are not good additions to the vegetable garden. Finally, bark nuggets float, so don't use them where they are likely to be washed away or could clog drains.

Stones and rock: As water conservation and high-temperature days have affected garden maintenance, creating landscapes that are easily maintained in hot, dry weather — or xeriscaping — has become more popular.

Rock is used mainly as a decorative element. A layer of landscape cloth or plastic mulch is installed over weed-free soil to prevent growth, atop which is placed a layer of rock. Be careful to keep the rocks swept in place and when mowing nearby to avoid thrown rocks.

Cover crops: A cover crop of grasses or legumes can be planted as a living mulch to help prevent weeds from springing up between growing seasons. Planted in the fall and then harvested or plowed under in spring, grasses such as wheat and oats and nitrogen-fixing legumes are a green answer to conserve moisture and nutrients.

Susan Smith-Durisek is a master gardener and writer from Lexington. Email: durisek@aol.com. Blog: Gardening.bloginky.com.

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