Topic: Agriculture and food "When the planes still swoop down and aerial spray a field in order to kill a predator insect with pesticides, we are in the Dark Ages of commerce. ~ Paul Hawken

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).