Dyed mulches seem to be a common material used among homeowners and commercial landscapes today. Unfortunately, dyed mulches in black, red, and even brown is what is most available for purchase at big box stores, gas stations, and sometimes local nurseries.
It can be more difficult to find mulch that has not been dyed, but usually there is at least one brand available for purchase at any store. Local nurseries or bulk mulch companies tend to have more natural options.
Dyed Mulch Wood Sources
Most of the wood used in dyed mulch comes from recycled wood sourced from lumber scraps, wood pallets, and wood reclaimed from construction demolition waste. While recycling is great, it’s a concern because there is the possibility of contamination from lumber sources containing toxic chemicals.
Recycled wood waste can contain chemicals such as creosote and CCA (chromated cooper arsenate) which is used as a wood preservative. Recently, arsenic based wood preservatives have been banned, but still remain in older wood, which could still used as a source for the mulch. This type of wood can also have paint and varnishes on it. Since the wood is chopped into small pieces and has more surface area, larger amounts of the toxins can leach into the soil as the wood breaks down.
Wood pallets can be contaminated when the chemical products being shipped on them spill onto the pallet. They can also be sprayed with chemicals such as fungicides, insecticides, rodenticides to preserve the pallet, the products, and to prevent pests traveling on the pallets.
While you may think the dye used in dyed mulches would be the toxin, is not the main concern. The dye is used to disguise the variances of the chipped wood since the wood comes from a variety of sources. Disguising materials with paint, dyes, and other processes is common practice in manufacturing to save costs. Since the wood is dry, it easily absorbs the dye.
There are primarily two different types of dyes used in the mulch. Carbon based dyes are similar to ones used in ink and cosmetics. Most of the dye though seems to be made of iron oxide, which will leach into the soil. It is a type of dye often used to dye flowers in the floral industry. This dye can rub off the mulch and stain clothing and skin. There is currently no evidence that the dye used to color wood mulch is toxic. However to me the dye is unnecessary so why take a chance? We do not need to add more pollution to the soil and groundwater.
Mulching Edible Plants
I would avoid using dyed mulches near plants that will be food sources or in areas where any human food producing plants may be planted in the future. It is probably also not a good idea to use this type of mulch in areas where children or pets will be. There is also concern for wildlife that eats the plants in our gardens. Birds eat berries, seeds, and insects. Good insects like pollinators use plants as food. It all gets passed down the food chain. I’d rather not poison the plants that anything is eating.
My Experiences with Dyed Mulch
I personally do not use dyed mulches because of the potential toxicity and because I do not like the look. When the dye fades or wears off by the end of the season or the following year, the chipped wood is very unattractive. This type of mulch can also form an aerobic crust which acts as a water barrier. Once it forms this crust, it does not break down and can contribute to plant diseases including root rot on trees.
The Mulch and Soil Council has developed a product certification program to help consumers know which soils and mulches comply with industry standards. In 2004, the mulch and soil industry set standards to prohibit the use of CCA treated wood in mulch and soil products. These certified mulches will have a MSC Certification logo on the package, and can also be found on the MSC website. While this certification process is a good thing, I would still be leary since a company may not be testing every wood source its using in the wood mulch.