Question: We had a large maple tree removed from our property. The company that took it down left a pile of fresh wood chips for us. Is it safe for me to use these wood chips to mulch my garden? If not, what can I do with them?
Answer: Mulch is good for gardens for many reasons. It cuts down on weeds, conserves soil moisture and stabilizes soil temperatures. As mulch breaks down, it also adds organic matter and nutrients to the soil.
The term “mulch” can refer to anything that's applied to the soil surface, not just shredded wood or bark products. Straw, hay, untreated grass clippings, compost and mushroom soil are some other commonly used mulching materials.
When it comes to using those fresh wood chips as a mulch in the garden, there are a few things to consider.
First, fresh wood chips are often available for free or a very low price from tree removal companies; that's a definite plus. But, unlike finished compost or even double-shredded bark mulch, fresh wood chips are in a state of very active decomposition.
These initial stages of decomposition require nitrogen. When fresh wood chips are used as a mulch, this nitrogen is pulled from the topmost inch or two of soil, causing a temporary nitrogen deficiency in this area. But as the mulch breaks down, the nitrogen is eventually released back into the soil (along with lots of organic matter and other nutrients), making it good for the soil in the long run.
This temporary nitrogen depletion is why fresh wood chips shouldn't be used as a soil amendment, only as a mulch. If you mix the wood chips into the soil, the zone of nitrogen depletion will be much greater, but if you keep them only on the soil's surface, the impacted area is far smaller.
Because of this temporary nitrogen depletion, it's best to use fresh wood chips around deep-rooted plants, such as trees and shrubs, rather than in the vegetable or perennial garden. Trees and shrubs acquire their nutrients from deep in the soil, and they won't even notice the nitrogen deficiency.
One simple way to avoid this issue and still use the wood chips on flower or vegetable areas is to allow the wood chips to age for a year before using them. You could also use them to mulch pathways or other areas without plant growth.
If you're concerned about fresh wood chips from diseased trees spreading the same disease to other trees and ornamental plants, research indicates that this is highly unlikely. However, experts at the Ohio State University recommend not using fresh wood chips from oak trees around other oaks. Though the devastating pathogen that causes oak wilt is unlikely to spread via wood chips, they suggest using fresh wood chips from oaks only around other tree species as a precaution.
No matter where you decide to use your fresh wood chips, as with other mulches, never pile them against tree trunks or other plants. Doing so leads to fungal diseases and bark rot, and will eventually kill the tree.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is jessicawalliser.com.
Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., Third Floor, Pittsburgh, PA 15212.
