Mulching makes good sense - Special Issue: Spring-Summer 1994 Garden Guide - Planting & Maintenance Guide

Sunset, Spring-Summer, 1994

Spreading mulch over soil that plants grow in is, in most situations, simply good gardening. But today, as much of the West faces periodic droughts and enforced water conservation, mulching is a flat-out necessity. Mulches have three primary benefits:

* They reduce evaporation of water from the soil. The potential saving is greatest in hot, dry climates.

* They reduce weeds that compete for water with desired plants. Mulches cover weed seeds and shade any seedlings, inhibiting growth.

* They insulate soil from extreme temperature changes. Mulches keep the upper inches of the soil cooler during the day, warmer at night.

Mulch can also prevent mud from splashing onto foliage and cushion falling fruit from injury.

A good mulch can even encourage earthworms, which aerate and enrich the soil. (The worst that can be said of some mulches--especially coarse-textured ones--is that they also encourage sow bugs and snails that like to hide in them.) To conserve water, mulch in late spring, once soil is warm. Apply mulch over the drip zones of plants (don't pile it against plant stems or trunks).

Commonly available mulch materials

Pictured above are three natural-material mulches often available in garden centers. All are noncomposted; as they decompose in or adjacent to soil, they will outcompete plant roots for their most important nutrient--nitrogen. For this reason, they don't make good summer mulches without additional nitrogen fertilizer.

To use these materials safely as mulch and prevent nitrogen deficiency, apply 3 pounds of actual nitrogen per cubic yard of material. Use controlled-release nitrogen fertilizers, such as ureaform (38-0-0). In fall, any of them can be rotary-tilled into the soil to decompose over the winter and improve soil. Aged redwood sawdust costs $6 for a 3-cubic-foot bag; in bulk, it runs about $22 per cubic yard or 14 cents per square foot, 2 inches deep. In spring, apply a 1- to 2-inch layer around vegetables and ornamentals.

Decorative bark is mostly white fir or pine. Sizes are graded: 1/4- to 3/4-inch bark is usually called pea, 3/4- to 1 1/2-inch is acorn, 1 1/2- to 2 1/2-inch is jumbo. Bark chips range widely in price: $1.25 to $3 per cubic foot in bags, $20 to $40 per cubic yard in bulk.

Shredded bark is slow to decompose; the irregular pieces hold well on slopes and in windy areas. It costs about $7 for a 3-cubic-foot bag; in bulk, it costs about $20 to $40 per cubic yard. Use it in 2-inch layers.

How much mulch?

One cubic yard (27 cubic feet) of mulch covers 108 square feet with a layer 3 inches deep. A 3-cubic-foot bag covers 18 square feet to 2 inches deep.