Does Dyed Mulch Affect My Vegetables?

Dyed Wood Mulch

• Manufactures dye wood or bark mulch in bulk using colorant in 55-gallon drums. Homeowners buy colorant in smaller quantities to dye faded garden mulch. Manufactures claim that the mulch and colorant products they sell are safe for plants and animals. According to Holly Scroggins of Washington State University, content reports for colorants are incomplete or show common solvent or petroleum products in mulch dye. Gardeners considering dyed wood mulch products must decide if the aesthetic benefits are worthwhile.

Toxic Mulch

• Dyed or natural wood mulch develops a buildup of toxic liquids and gasses when improperly stored. Safe mulch smells like healthy garden compost or freshly cut wood. Mulch that gives off a sour or rotten-egg smell is suspect. Sour mulch damages plants, causing yellowing leaves, defoliation and eventually plant death. Sour-smelling mulch spread out on a driveway for a few days cures through exposure to fresh air. Dyed mulch benefits from air curing before use to set the dye.

Plastic Colored Mulch

• Commercial growers have used plastic mulches on vegetables beginning in the early 1960s. Plastic mulches affect the microclimate around each plant, altering temperature and moisture retention. Soil temperatures under black mulch are 3 to 5 degrees Fahrenheit higher than the surrounding soil. Clear plastic mulch holds water droplets under its surface, keeping the soil 6 to 14 F warmer than bare soil. White mulch slightly increases soil temperature. Red and white mulches increased the yield of tomato plants infected with nematodes, according to the Journal of Nematology.

Reflecting Mulch

• The surface of reflective plastic mulch affects plant growth and development by lowering soil temperature and extending the season in hot climates. Silver mulch increased the yield of Irish potatoes compared to other colored mulches or bare ground. This may be attributed to the cooler soil, according to the University of Connecticut. Infrared-transmitting mulches combine some of the benefits of white and black mulches, controlling weeds and increasing soil temperature slightly.