Black mulch serves both function and style in complementing a garden or landscape. The product is capable of not only providing a unique look to gardening or landscaping, but can also help protect plants from reflective light and keep root systems warmer. Despite these advantages, there are also some dangers of black mulch that should be kept in mind.
Black mulch comes in three main varieties: wood, rubber and plastic. Each has distinctive advantages, but also could have some major disadvantages which could be harmful to your garden, and perhaps even people.
If the mulch is a wood mulch that has been dyed, you should know what that dye is. Many black mulch products made using wood use black coming from a carbon process, similar to the color from coal. In most cases, this coloring is harmless. Other dyes may not be. Sticking to a natural coloring process helps ensure the coloring will be harmless to other living things, including plants.
Some of the hazards can be quite deadly. Black mulch made of rubber contains zinc, benzene and other potentially toxic substances. Zinc can stunt the growth of plants. If you are using the mulch in a vegetable garden, it is possible some of these chemicals will get into the consumed portion of the plant. Benzene is a carcinogen, and can be very harmful if ingested.
While black mulch in a garden may be easy enough to remove by hand, the mulch may also be used in a commercial setting. This makes removal much more difficult if it is a synthetic like plastic. Wood products will eventually decay, but black plastic mulch will not break down and will need to be removed by hand. Otherwise, it could remain in the environment and even be considered a pollutant.
The temperature of black mulch is another possible danger, especially to plants. Penn State University published a study noting the soil temperatures under black mulch are five degrees higher than bare soil during the day. This may be beneficial to many garden plants, but could also be quite harmful if the soil temperature is too high. It may even lead to stunted growth.