Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu
Over the last 10 years, Penn State vegetable researchers have conducted extensive tests on the effect of mulch color on various vegetable crops. There have found some significant increases in yield for specific crop-mulch color combinations. Growers in Delaware have reported good success with the use of red and dark blue mulches in certain crops. The following is a summary of some the Penn State results and some of our recommendations based on grower experience.
Black Mulch
Black mulch is still the most economical mulch for growers. Most vegetables have been successfully grown on black plastic and it is the recommended mulch for general use. It does not offer as much soil heating as some other colors in the spring and causes excess bed heating in summer plantings.
Red Mulch
Tomatoes and eggplants had an average 12% increase in marketable fruit on red mulch when compared to black plastic in Penn State research. There was also some reduction in early blight in tomatoes on red mulch.
Silver and Reflective Mulch
Silver and reflective mulch tends to repel aphids. Peppers had an average increase of 20% in marketable fruit yield and also had increased average fruit size on silver mulch when compared to black plastic in Penn State research. Silver and reflective mulch has shown advantages for later season crops susceptible to aphids and the virus diseases that they transmit.
Dark Blue Mulch
In Penn State research, cucurbit crops benefited from the use of dark blue mulch. Cantaloupe yielded 35% higher on dark blue mulch compared to black plastic. With cucumbers there was a 30% increase in marketable fruit and summer squash yielded 20% higher on blue mulch when compared to black. One drawback to blue mulch is that it tends to attract thrips. Blue mulch should not be used with crops susceptible to thrips problems such as peppers and tomatoes.
Yellow Mulch
Lowest yields were seen with yellow mulch on many crops. Yellow mulch tended to attract insects and is not recommended.
Green IRT Mulch
Pepper yields were the same on green mulch compared to black plastic. Green IRT mulch warms soils more than black plastic but has the advantage of better weed control than clear plastic. It is best used with very early planted warm season vegetables.
Clear Mulch
Clear mulch is sometime used for sweet corn and other warm season crops where maximum soil heating is needed for very early plantings. The disadvantage with clear mulch is that it allows weed growth and should only be used in fumigated soils or crops where broad spectrum herbicides are labeled for application under plastic.
White Mulch
White mulch is used for summer plantings where black plastic mulch can cause too much bed heating. It is especially useful to reduce heat necrosis of transplants around transplant holes, which can occur with summer plantings on black plastic. This is where stem tissue dies right at the level of the plastic and transplants collapse. White plastic is also beneficial for summer crops of plants with roots that are sensitive to high soil temperatures, such as day-neutral strawberries.