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Fresh Wood Chips As Mulch?Since the major ice storms in Virginia counties caused severe damage to trees, many counties are giving away all the mulch that one can haul. Concerns have arisen as to the effect, if any, that this fresh mulch will have on plants if put down now.Per Dr. Donald Rakow, Director of Cornell Plantations, there are three primary concerns. First, is that any diseases on the wood can be transferred to ornamentals. According to George Hudler (also at Cornell -- Department of Plant Pathology), it is very unlikely that the right combination of factors (pathogen, susceptible host, environmental conditions) will come together to spread diseases in this way. The second concern is that naturally occurring allelopathic chemicals will be transferred directly to susceptible plants. In research that Dr. MacDaniels conducted in the 1950s, he found that he could not induce wilting in susceptible solanaceous plants when planting them directly into fresh black walnut wood chips. Many do not consider this a problem, but there has been no follow up on this research. Bark and fruit contain the concentration of juglone, but very little is in the wood itself; this may account for Dr. MacDaniels' findings. Lastly, there is the concern about the fresh wood chips tying up nitrogen during their decomposition. An article by Frank Gouin (University of Maryland) states that wood chips (as opposed to pine bark) have a very wide C:N ratio, and that they do cause significant nutrient deficiencies, particularly for herbaceous plants. Mark White (Professor, Wood Science and Forest Products, Virginia Tech) has done research on the pH of wood leachates and reports that they are quite acidic and could significantly change soil pH depending on the volume used. Since they can be in the pH 4 range, the acidity could both damage the plant and plant roots immediately and reduce could reduce soil pH with repeated applications. Large trees and plants that require an acid soil can survive this situation better than tree seedlings and most herbaceous plants. According to Jim May (Research Associate, CSES, Virginia Tech), if fresh wood chips are applied in too thick of a layer, the heat generated as they begin to compost can injure herbaceous plants. More research is being conducted by a PhD student at Cornell, so additional information should become available in a few years.
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