The type of colorant used in mulch depends upon the manufacturer. Some companies make their own colorant while others buy it from distributors. Colorant typically contains some formulation of water, pigments, resins, humectants and other additives that may or may not be toxic. The type of colorant used also depends upon the type of mulch (raw lumber or recycled wood products) being colored.
Recycled Wood vs. Raw Lumber
While recycling is good for the environment, recycled wood mulches have the potential to carry toxic chemicals into plant beds. Mulch manufacturers may use wood from old pallets, crates or other wood products that contain CCA pressure-treated lumber (which contains arsenic). Mulch composed of raw lumber is free of chemicals and is safe for soil, animals and humans.
Mulch Coloring Process
Specialized mulch coloring equipment systems, which include a hopper, coloring tank, conveyor or auger system and electrical controls, are used to color landscaping mulch. Untreated mulch is loaded into the hopper. It is then fed into the coloring tank, where it is sprayed with colorant and water. The mulch is stirred by agitating paddles to coat all pieces evenly. When the color process is complete, the mulch is distributed by conveyor belt or auger onto large piles to await distribution.