Recently, several types of crop-specific, or "designer," mulches have been developed. For example, tomatoes are partial to red mulch while potatoes favor pale blue or white. Squash and eggplant have responded favorably to blue. Research has shown growing tomatoes on red mulched beds, rather than conventional black mulched ones, can increase harvest of quality fruit by 10 to 15 percent.

It's not the colors of the mulch that enhance yield, but the difference the colors make in the light reflected onto the plants.

Research on the effects colored mulches have on plant growth and yields is ongoing. No doubt other colors will be identified as beneficial to certain fruit and vegetable crops, and new products will be offered as research becomes conclusive.

Various types of woven and perforated mulches that are porous to air, water and nutrients also can be used effectively on permanent raised beds. These "weed mat" or "landscape fabric" types of mulches provide excellent weed control and can be used in combination with sprinkler irrigation systems. Their heavier design endows them with several years of service life. Consequently, they are ideally suited for use with perennial crops such as small fruit.

Expect to pay more for porous mulches. Also, don't expect the same soil warming benefit from porous mulches that can be achieved using thinner film mulches.

Plastic mulch film generally comes on rolls 4- to 5-feet-wide. Less common 3- and 6-feet-wide rolls also are available.

Mulch films are available in various lengths with 2400- and 4000-foot rolls most common. Shorter lengths are available from mail order catalogs. See the appendix for a list of companies carrying plastic mulch.

Mulch films are available in either smooth or embossed surface finish. The embossed film hugs the bed better and is not as prone to loosen during warm weather. Expect to pay a little more for embossed film.

Ranging in thickness from 1 to 1.25 mils (1 mil = 1/1000 inch), mulch film is thinner than the woven fabric mulch sold at home improvement centers. Because it is very thin, don't plan on using the mulch for more than one growing season.

Before you decide on the use of plastic mulch as a component of your raised bed gardening system, consider the increased amount of maintenance required. Growing crops on plastic mulch also is a whole new game when it comes to water and nutrient management. A thorough understanding of the use of tensiometers to schedule irrigation and of fertilizer injection equipment to inject nutrients into the drip system is required to realize the full potential of the mulched growing system.