Environmental Pros and Cons of Recycled Red Mulch
Mulch comes in many different forms and most types of mulch can help to promote growth and ward off pests, simply by virtue of the environmental protection they offer. Red mulch can be particularly effective at producing larger plants, particularly strawberries and tomatoes, while red rubber mulch can provide more effective insulation than some other forms while also allowing moisture to reach the soil uninhibited.
However, some red mulches have also been reported to damage plants. This has given rise to the rumour that red mulch is toxic and should not be used. Red mulch itself is not toxic – that is, the toxicity has nothing to do with the red paint – but some of the materials which can be used to make it potentially are.
Some wood purchased from construction and demolition sites, for example, has been treated from chromated copper arsenate and has been shown to contain arsenic. Mulch made from wood treated with chromate copper arsenate is potentially poisonous. Rainfall could cause leaching of the arsenic into the soil, either killing plants or causing toxic build up of arsenic in fruit and vegetables that are then passed on to animals and humans.
Similarly, processed rubber from tires may contain cadmium, chromium, aluminium, copper, iron, manganese, molybdenum, selenium, sulphur and zinc. Zinc is often found in particularly high concentrations and this too can leach and potentially damage affected plants and soil. Scientific research is still inconclusive as to whether mulch made from rubber tires is dangerous, but many gardeners have reported problems when using it.