Red mulch is a popular choice because plants seem more green and vibrant against the red background. Some people enjoy black mulch as well, especially in gardens with multi-colored flowers. While there's no proven benefit to using red mulch other than an aesthetic one, there are reasons you might not want to use it because of the effect it can have on your plants.
TIP: Our expert gardening advisor, Susan Patterson adds, "Mulch helps retain soil moisture and should never come in direct contact with tree trunks. Never apply more than a 3-inch layer of mulch."
Choose Brand Name Red Mulch
While there are some drawbacks to colored mulch, you can still enjoy it and help your plants by choosing a popular brand name of mulch. Read the bag and even contact the company to find out about the wood and the dyes used in making the mulch. Many brands are colored with iron oxide which is not harmful, as it's essentially rust. Other colorants are carefully controlled and as safe as or safer than any water-based paint. Some companies even use vegetable dyes and other natural products.
In the early years of dyed mulch, the manufacturers used toxic dyes. These dyes do still find their way into the system. Check any mulch you buy to be sure it does not contain petrochemical dyes. Most commercial dyes are safer today, but they are still manufactured with petrochemicals that can be hazardous, particularly to vegetable gardens. Look for red mulches that specifically mention biodegradable pigments if you are going to buy red mulch.
TIP: Susan advises, "If you have a truly organic garden, always choose a colored mulch that has been dyed with organic materials. As the mulch breaks down in the garden the dye will be released into the soil."
Red Mulch Manufacturing
For any kind of mulch, you should find out where the wood comes from. Some red mulch is produced by land clearing companies. The wood in these mulches comes directly from the raw lumber. As land is cleared the logs are sent to a lumberyard where small pieces are turned into mulch. This type of mulch is the best.
Other manufacturers used recycled wood. They take old crates and pallets and turn that wood into mulch which they color with mulch dye. Even with the safest dye, this mulch should not be used. There's a high chance that CCA (chromate copper arsenate) wood has gotten in the mix and has been ground into mulch.
Dangers of Pressure-Treated Wood
CCA wood is also called arsenic-treated wood. This results when lumber is treated with CCA which contains chrome, arsenic and copper. If wood is called pressure-treated wood, it may have been treated with CCA. The use of this process was phased out in 2003 when the EPA became aware of the dangers of arsenic leaking from the wood. Arsenic is a carcinogen that can cause various types of cancer. Make sure your red mulch was not created from recycled or salvaged wood so you can be sure it doesn’t' contain arsenic.
Colored Mulch Problems and Benefits
Some people claim that red mulch improves tomatoes and strawberries because the red color reflects more light onto the plants. This hasn't been tested in a controlled environment, so for now it is unsubstantiated. Avoid walking on the red mulch (or any colored mulch) because the dye can transfer to your shoes and track in areas you don't want it.
TIP: Sisan adds, "Colored mulch will fade more quickly than natural mulch and has to be replaced frequently."