By Xander Rose
As I’m moving wood chips provided by a local arborist to put around our fruit trees at Raintree Nursery on a recent winter’s day (fortunately without too much rain), I think to myself about the importance of mulching fruit trees. There are many benefits and reasons to mulch trees, as well as different ways to do it.
I’m happy we had a big pile of new wood chips delivered this December! Bits of chopped up green hemlock branch tips, verdant cedar boughs, bright red alder phloem and inner bark, chunks of fir and maple wood, this wonderful woodsy mix will transform the grassy ground around our fruit trees. I scoop up the multicolored wood chips into the bucket of one of our tractors and dump them carefully around an apple tree, being careful to not damage the tree’s lower branches or trunk whilst doing so and to not let chips fall in the area immediately around the tree’s base. This is preventive medicine! I want to keep the base clear of both vegetation and mulch, keeping it exposed for healing air flow and sunlight. Ideally, the area a couples inches out from around the trunks should be kept clean and clear (a little hand weeding). With fewer trees than in our grand orchard, putting sand or pea gravel right around can nicely help accomplish this.
Fortunately for us, we have well-drained ground with some sand and rock already in it. Our rich black silty loam (technically Cinebar silt loam and Newaukum gravelly loam, according to the Natural Resources Conservation Service) has some grit in it, from sand on up to rocks only two hands easily grab. Fruit trees shed leaf litter and some bits of branches not removed while pruning. These break down in a lasting, noticeably woodland way only around the especially large fruit trees that spread 15 feet across or more. Elsewhere in the orchard proper, grasses dominate (fescue, quackgrass, orchard grass, and others I would like to learn). Forbs like small dandelions, plantain, clover, and buttercup play a lesser role. Grass dominated ecosystems are called prairies or savannas. Fruit trees originated in woodlands. As Michael Phillips describes in his The Holisitic Orchard: Tree Fruits and Berries the Biological Way, orchards are essentially like woodland edges. Yet, for various good reasons we prune the trees and mostly burn their branches to maintain good orchard hygiene. We don’t let old fruit trees fall apart and rot away as in a wild woodland. This is an orchard, not a “messy” forest! Clean, disease-free wood chips from totally unrelated native species are an important input to boost the woodland aspect of this orchard.
One of the most obvious reasons for mulching fruit trees is to suppress grass and other weeds that may compete with trees for water and other nutrients. Scything, mowing, weed whacking, or grazing can help control grass, too, but not always easily right under the tree. Controlling weeds is especially important when establishing young trees that have limited root systems and need lots of watering.
Mulching also reduces competition from grass and other weeds like dandelions, plantain, clover, or whatever other ground covers and herbs grow in the orchard. A fruit tree’s feeder roots extend to just outside of the dripline of the tree (the edge of its outermost branches), so having putting mulch under the tree up to the dripline will help reduce competition for resources (including water) from other plants. Trees with low branches may be difficult to get under for mowing or other mechanical grass control options. Herbicide may not be desirable. So, mulch is the answer for suppressing grass around the tree.
Mulch can come in many forms besides wood chips, including cardboard, plastic fabric, lawn clippings, leaf litter, and straw. All of these besides the plastic are highly desirable because they decompose over time, enriching the soil ecosystem. Mixing well-rotted compost or manure into mulch can speed up this process, though care should be taken to not over fertilize and “force” fruit trees, especially young trees. Ramial wood chips are wood chips made from small diameter branches and ideally chipped twice, meaning that there is more sapwood (primary xylem), phloem, and bark (meaning more live or recently alive tissue) relative to true wood (secondary xylem, meaning dead tissue, heartwood) than wood chips from whole trees. Wood chips from branches decompose faster because of this and provide nutrients sooner. It’s important to understand that part of how decomposition works is that bacteria basically use nitrogen to digest carbon-heavy matter like plant cellulose. Wood chips from branches give bacteria and other decomposers more to work with! So, the home orchardist can make their own ramial wood chips from pruning their own trees, though of course the branches must not be diseased.
Our wood chips are locally sourced and free. In many areas private arbor companies, municipal forestry or road departments, or utility companies that cut down and chip trees may provide free wood chips for pickup or even delivery. The backyard orchardists might not be able to take all the wood chips an arborist would want to drop in a driveway if the deliveries are ongoing, but it’s worth looking into because many arborist would just love a free place to dump chips. Check out this free service to get connected to arborists’ wood chips: https://getchipdrop.com/.
Wood chips I’ve used at Raintree have come from western red cedar, red alder, big leaf maple, western hemlock, and Douglas-fir trees. Different tree species make for different contributions and considerations as mulch for fruit trees. The cedar smells nice, but I only dare put it around old and well-established trees. This is because these “cedar” trees, which are technically not “true” Cedrus cedars (family Pinaceae) and are actually members of the cypress or redwood family Cupressaceae, produce chemicals that can inhibit the growth of other trees. Conifers as sources of wood chips in general might acidify the soil overtime, so that is something to be aware of when using them for fruit trees. I definitely don’t advise too much conifer mulch (especially not western red cedar or other cypress) around young fruit trees. Beware of other species that may be more or less toxic, such as walnuts (Juglans species) and (Robinia species). Faster-decomposing deciduous trees like alder, maple, willow, and birch can provide better mulch. Alder is especially great in our case. Willow wood chips have been shown to boost fruit trees’ immune systems (learned on the Orchard People podcast, see sources below)! Because bacteria use nitrogen to decompose wood chips, don’t overuse wood chips around young trees that have small root systems looking for nitrogen. Just enough to suppress grass around the tree is advisable.
In the long run, mulch, especially wood chips, help promote healthy woodland soil for fruit trees by breaking down and feeding the whole soil community from bacteria and fungi on up through nematodes, springtails, earthworms, ground and rover beetles, millipedes, centipedes and the tree itself. Throw in a moles and voles, maybe a slightly pesky skunk, rabbits and the hawk they feed, robins who eat earthworms and a flicker who eats ants, and the orchard comes into focus as part of a whole ecosystem.
Happy growing! Because, after all, change is the only constant. -Xander Rose
A few useful resources:
Phillips, Michael. 2012. Chelsea Green Publishing Company: The Holisitic Orchard: Tree Fruits and Berries the Biological Way.
Poizner, Susan. “The Ultimate Guide to Fruit Tree Mulch” Accessed 12/15/2020: <https://orchardpeople.com/fruit-tree-mulch/>. (Also check out her podcast: “Orchard People”).
Poizner, Susan. "Episode 36: Willow Mulch for Fruit Trees" Orchard People podcast, with guest Dr. Glynn Percival of UK and Ireland Bartlett Tree Research and Diagnostic Laboratory. Accessed 12/15/2020: <https://orchardpeople.com/willow-mulch-for-fruit-trees/>.
UMass Extension. 2012. “ Mulching Tree Fruit and Small Fruit” Accessed 12/15/2020: https://ag.umass.edu/sites/ag.umass.edu/files/fact-sheets/pdf/mulching_fruit.pdf.
Fig 2. A specially designed circular piece of plastic fabric helps conserve water and suppress grass around a newly planted tree. Using stakes, the circle can be moved and reused around another young after a couple years. However, an inorganic mulch like this will not biodegrade (and thus not contribute to the soil community) and is only acceptable as a temporary covering around young trees.