Mulching with Arborist Chips

Reader Contribution by Blythe Pelham
Published on April 17, 2017

In my recent blog about Garden Thriftiness, I mentioned using free mulch from local tree services in the garden. I decided it was imperative to include a few key facts and pointers about plant and people safety when using said mulch.

You might want to ask the tree service what type of trees are in the mulch mix that they bring you. There are some trees that are not a good mix for certain plants and other trees. For instance, the walnut family (particularly black walnut) is toxic to many annuals, perennials, and trees. If you are able to let bark chips sit for six months, they should be usable without negative consequence because the toxicity diminishes.

Toxicity. Many of us don’t have the luxury of space to let a pile mulch just sit for undetermined amounts of time. For this reason, simply knowing what is in your mulch will be more beneficial. I learned this by a random drop off of mulch that I discovered contained black walnut. I immediately researched and found out about the toxicity. Though my newly planted apple trees were not on the danger list, I wanted to take no chances about their health. While it looked a little strange, I put safer rings of matured mulch around those trees and used the questionable mulch in areas with plants not at risk (see link above for a list of plants).

Disease. Using arborist mulch in this way is not conducive to spreading disease. You should be good to go as long as you are not tilling in fresh mulch as most diseases need easy access to the roots. Topical application is safe in most cases. Remember to leave a small ring of ground around your small plant, shrub, or tree. It is beneficial to most plants to have breathing space around stem or trunk and not to be smothered by the mulch. In fact, it can be very unhealthy for most plants to have mulch piled up around their stem or trunk.

Composition. Tree service mulch would drive anyone with OCD bonkers. The composition of the pile is quite diverse (see photo above). Most piles include long sticks (that can poke and puncture) and parts of branches, shredded leaves or needles, composted matter from dead wood, and pockets of mold. This latter could be a problem for people with certain allergies or pose a health risk if moved without a breathing barrier mask.

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