In this column we are going to answer your questions on mulch. In the first issue we discussed the three best types of mulch hence this week we will look at the three worst types. 

Researchers have found that healthy fertile soils with low insect and disease pressure have one thing in common, a 30:1 ratio of carbon to nitrogen. This is an important and common ratio found throughout natural systems. 

COLORED MULCH – Colored or dyed mulch can be found in many colors from red to green and blue. The most common are red and black. The first problem with the dyed mulches is the carbon: nitrogen ratio. To get the dyes to stick to the wood producers use raw wood from pallets, crates and other trash wood. This type of wood has a C:N ratio of over 500:1! Hence when it is placed on the soil microbes will start to break it down. To do this they need lots of nitrogen. To get this extra nitrogen they pull it from the soil away from plant roots (microbes always eat first). When plants do not have enough nitrogen they are far more susceptible to insect and disease issues. 

The second problem is the black mulches. Black does not occur in nature except under anaerobic conditions (this means without oxygen) where the soil is sickly and full of bad microbes (pathogens). The most common black colorant is carbon black which is a byproduct of the chemical industry and a known carcinogen. 

For additional information see: 

http://www.natureswayresources.com/infosheets/coloredmulch.html 

ASHEN MULCH – This is another type of black mulch. The colorant is ash from the burning of coal. When coal is burned all the toxic materials end up in the ash including heavy metals. This ash is very alkaline and when mixed with the raw trash wood (like the colored mulch above) and it chemically burns the surface layers of the wood black. After a few weeks it gets this ugly grayish color hence the name Ashen Mulch. In addition to the high carbon: nitrogen ratio it is also very alkaline and can cause nutrient tie-up problems. This stresses the plant leading to increase insect and disease problems. For additional information on ashes please see; 

http://www.natureswayresources.com/resource/infosheets/boiler.html 

RUBBER MULCH – This is the third type of very bad mulch often sold in garden centers. It can be found in many colors however it is made from old tires and is very bad for plants. It is toxic and potentially dangerous. For additional information see: 

http://www.natureswayresources.com/resource/infosheets/rubber.html 

John Ferguson is the owner of Nature’s Way Resources and co-author of the book Organic Management for the Professional.