In this article, we tackle some of the commonly held concerns we’ve heard regarding the use of arborists wood chip as a landscape mulch material. It seems most of the concerns are contrary to the results of scientific research trials, so we feel it incumbent upon us to explain some of these ‘myths’.
Wood chip will ‘rob’ my soil of nitrogen and is bad for plants
In general terms, woodchip mulches do have a high carbon to nitrogen ratio and will increase the essential nutrient levels in soils and plant foliage. Fresh woodchip mulch (less than eight weeks old) can temporarily reduce the supply of nitrogen take up at the mulch/soil interface level, but this is a good thing as it will serve to inhibit weed seed germination. Established plant roots below the surface will not be affected and bulbs, tubers and corms are likely to thrive. It is, however, inadvisable to use high carbon : nitrogen woodchip in annual beds with fine, shallow root systems or on vegetable plots. If you still have concerns, the woodchip that Gristwood and Toms supply, has been aged for around 8-12 weeks. Further, as long as the wood chip has been on the site for at least six months, the C:N levels won’t create nitrogen deficiency in plants or crops if worked into the soil.
Wood chip will acidify my soil
There is no evidence to support this. It is very difficult to significantly change the pH level of the underlying soil without the use of chemicals.
What about diseases – can using chip from diseased trees infect my trees or plants?
Studies show that wood chip used correctly as a top-dress mulch material does not transmit pathogens several inches from the mulch, through the soil to the roots of healthy trees and plants. However, it is important to clarify that you should not use wood mulch as a backfill material or incorporate woodchip into the soil. Neither should mulch be piled up against the trunks of trees and shrubs as opportunistic pathogens can be transmitted this way.
Fungal species are generally decomposers, not pathogens. If you have good healthy soil, beneficial fungi will out-compete opportunistic pathogens (such as Phytophthora) anyway.
Will wood chips will attract pests?
No. In fact, wood chips act as a repellant to many types of pest.
Credit to Dr. Linda Chalker-Scott and her extensive research and scientific publications that have been used to inform and support this blog – in particular her ‘Horticultural Myths’ column.