Question: Garden catalogs are selling various colored plastic mulches. Are they more effective than black?
Answer: Plastic mulches in almost every color of the rainbow can be found in a variety of gardening catalogs. Black, white and clear are the most common and have been around for a long time. These types of mulches have several advantages for the home gardener including extending the growing season, weed and insect management, retaining soil moisture and increased yields.
As to which is best, the research is still going on but here is what we know of at the present time.
Black plastic mulch is the most widely available and the least expensive. It is excellent for keeping the weeds from taking over, and it warms the soil during the growing season. Research at Penn State has shown the soil under black plastic is five degrees warmer at a 2-inch depth and three degrees warmer at a 4-inch depth. This allows you to set out plants earlier, leading to earlier yields.
White plastic mulch has the opposite effect. It keeps soil temperatures cooler than soil covered with black plastic. It will keep weeds down and retain soil moisture, but organic mulches such as straw will do the same at a cheaper cost.
A newer colored mulch is brown plastic mulch, also known as Brown Infrared Transmitting (IRT) mulch. Not all brown mulch is IRT so make sure it is described as such before purchasing.
The best mulch for heating the soil is clear but it has no weed-suppressing qualities. Brown IRT is comparable to clear in heating the soil and has the weed-suppressing properties of black plastic mulch.
Research by the USDA and Clemson University on red plastic mulch showed it performs well on certain crops. Tomatoes yielded 20 percent more fruit, basil had larger leaves and more succulence, and strawberries smelled better, tasted sweeter and had higher yields. Green IRT mulch showed optimistic results when growing cantaloupes, according to research by Penn State and the University of New Hampshire.
Blue plastic mulch yielded higher amounts of cantaloupes, summer squash and cucumbers when compared to fruits grown on black plastic mulch.
Lastly, research on silver mulch was found to be a deterrent to aphids, whiteflies and cucumber beetles. It also was beneficial on crop yield when growing bell peppers.
Some of these mulches can be sturdy enough to be used for multiple years which is important to the environmentally conscious gardener. There are also plastic recycling programs starting as the use of these plastic mulches increases.
Mona Bawgus is a certified master gardener and consumer horticulturist with Rutgers Cooperative Extension of Atlantic County. Write to her c/o Rutgers Cooperative Extension, 6260 Old Harding Highway, Mays Landing, NJ 08330. Email: