Arborist Chip Mulch Much?April 03, 2015
Arborist chip material has gone from an unwanted by-product to an impossible-to-find commodity to a readily available and desirable garden good in just the past few years. So, if you’ve put off trying chips in your garden because you didn’t have luck finding them, read on to learn where they’re readily available these days. And, if you’ve skipped using them for any number of other reasons, I challenge you to read on and see if your excuses still hold up by the end of this article.
(Update: We do not sell arborist chips; this article does provide information that may help you find them in your area.)
What is an arborist chip?
Arborist chips are essentially anything an an arborist puts through their chipper. This means that they’re coarsely chopped up bits of branches, leaves, blooms, berries and anything else an arborist chops down.
As an arborist goes from job to job during a day, s/he may fill a truck with trimmings from a sheared laurel hedge, thick branches from a cedar tree and viable bits of fruit from a holly tree. Some of the material may come from healthy plants; some may come from diseased plants. Like anything you bring into your garden, chips are a mixed bag.
Why do arborist chips make great top dressing? Arborist chip material, which is a by-product of tree work, includes all parts of a tree. (Well, maybe not a lot of roots, but all parts of the top growth.) And, the chunks are in variable sizes.
Unlike bark mulches that tend to be very fine, arborist chips don’t compact into impenetrable mats that may dissuade moisture from flowing through them into the soil below. And, because they are made up of all parts of a tree — instead of just waxy bark layers — they retain and release moisture into the soil for plants to uptake as needed.
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Can I amend my soil with arborist chips? Absolutely. But, doing it in a passive rather than active manner is best. While fresh arborist chips are filled with loads of nutrients plant roots seek, the chips need to go through some level of decomposition in order for those nutrients to be formulated for plants. So, if you spread the chips over the top of the soil, worms, fungi and other soil microbia will seek them out as a food source. As they process the fresh chips, they’ll release nutrients plants can use. If, on the other hand, the fresh chips are cut into the soil, they may stunt plant growth for as many months or years it takes for them to decompose.
What are other ways to use arborist chips? In addition to working as a top dressing garden mulch, arborist chip material makes a great, inexpensive path material. Too, these chips are fantastic for sheet mulching projects to remove lawn passively. Chips can be cut into passive compost heaps. And, they make a great dog toilet material – it’s so easy to clean up poop on a chip! And, arborist chips can work for kid play zones too. We’ve even dumped some in a hugelkultur experiment.
Will arborist chips help stop weeds? Yup. A few inch thick layer of arborist chip material does wonders in weed suppression. Because the nutrients in the chips aren’t yet available to plants, weed seeds don’t tend to germinate in arborist chip mulch. However, weeds and perennials already growing under where arborist chips are spread will usually have no problem bursting through the soil and the chips. So, remove tenaciously rooted weeds and weed seeds before spreading your chips.
When and how much arborist chip material should be applied? Every garden situation is different, so there’s no single answer here. Generally speaking, arborist chips can be spread at a 2″-6″ thickness over garden beds. As with other top dressings, avoid piling them up at the base of trees and other woody plants. Spreading them in late winter, before weeds pop up and perennials emerge is ideal, but they can be applied — with care — at just about any time.
How should arborist chips be applied? Again, every garden is different, but the good news is arborist chips may not need to be applied as often as “finished mulches.” Since the material is fresh, it takes longer to break down than mulches that have already gone through some level of decomp. Replenish arborist chips as needed so soil doesn’t become exposed, which happens as the chips decompose and become one with the soil. In our garden, which is rich in sandy loam, we apply a 2″-3″ layer of chips every couple of years in our garden beds.
What if the arborist chip material comes from a diseased tree? In asking this question myself, I haven’t run into the often-mentioned scientific studies saying that potentially diseased chips can or cannot pread disease into garden beds. But, the consensus seems to be that they won’t. Chris Watson, Arborist and Horticulture Lead at the University of Washington Botanic Gardens responded saying, “…Some claim that chips must be aged/composted to kill the disease and some say using fresh chips from a vert.(icillium) infected tree cannot spread disease. A friend of mine works as a research scientist/diagnostician for a national tree company, he said they could not spread vert.(icillium) into soil from inoculated chips, no matter how hard they tried. I guess in theory it seems possible. We do receive a lot of chips from different sources. Our policy is to age the chips as long as possible, usually 1-3 months. This helps with other pathogens and weed seeds, too. ” Dr. Linda Chalker-Scott, who uses arborist chips in her home garden, has done scientific research on many mulches, and advocates the use of arborist chips doesn’t intentionally “cure” her own chips. Learn her reasons and more about her research here. And, if you wish to go a bit deeper on the subject, this WSU Fact Sheet on arborist chips may help. And, in case you’re wondering, ours are never intentionally aged before spreading. It may take us a while to get the entire load spread, so the ones at the bottom of the pile tend to age passively until we get to them.
Will arborist chips attract termites and other nasty bugs? Years ago I created a small footpath using cedar “play chips.” These chips are usually produced from cedar and aren’t quite arborist chips; they’re the cleaner cousins seen in playgrounds everywhere. One warm summer evening, we watched a huge flock of termites fly out of the pathway. It was like a fluttering cloud arising from the path, and flying away. They didn’t attack any structural wood in our garden or home. Whether the path had attracted them or they came in on the chips in the first place is a mystery. And, a client in Southern California had a load of chips delivered to his home from a nearby golf course where a tree was being taken down. The chips were spread near the foundation of his home, and not long after he was calling an exterminator to deal with silverfish, which the exterminator claimed were notorious for invading SoCal homes with gardens topped with chips that met up with house foundations. And, yes, slugs and wood lice do like to spend time in rotting wood, so they may show up in wood chipped areas, but in our experience they’re balanced out by the beneficial creatures and properties the arborist chips provide. Other than that, I refer you to Dr. Chalker-Scott’s article via the above link that discusses her findings how chips may or may not attract unwanted insects.
Aren’t kind of junky looking? The looks of arborist chips seems to be the #1 turnoff. Well, if you can’t see the beauty in them, then maybe you’ll be hooked on the scent. If you’re fortunate enough to get a truckload of arborist chip filled with fresh cedar or another aromatic tree, your garden will be filled with the fragrance of a forest. So close your eyes and breathe deep if that’s what it takes!
Where can I get arborist chips? Today, there are a few ways to get your hands on arborist chip material. As always, if you’re having a tree pruned or taken out, you can ask your arborist to leave your chips on site. Or, you can call your arborist and ask that s/he drop off a load for you. Depending on the arborist, you may be charged for the load, and you may not be able to tell them how many yards you want them to leave – you’ll get what you get. Here in the Seattle area, bulk garden material suppliers are beginning to sell (and deliver) arborist chips. At the time of writing this article, The Dirt Exchange is offering arborist chips at about $24/yard + delivery, which is over $10/yard less than the finished mulches they also sell. We’ll see how long that lasts! (Updated 7/2016: There are registries such as Chip Drop where you may be able to connect with your local arborists to order chips. We have not used these services, so please let us know how they work out should you try them!)
And, as with firewood, take care to use chips from near your location.
I have a load of chips coming but I can’t spread them immediately – what to do? This is a job for the giant blue tarp. Yep, get ready to be that neighbor. When I’m expecting a delivery, I lay out a large tarp on my driveway. I pull some of the tarp over the nearby fence. The truck dumps on the portion of the tarp on the drive, and I cover the pile by folding over the remainder of the tarp (or using a second tarp on top if the load is particularly large.) Then, I weight down the top with a few large rocks or logs. This does a few things. First, the bottom tarp will protect the driveway from staining and will be easy to clean up when I finish spreading the chips. Second, the top layer of the tarp will protect the chips from rain; the drier the chips, the easier they are to spread. Third, by keeping the chips dry, nutrients won’t run off from a wet pile. Fourth, on hot days the tarp will trap heat, helping any stored chips begin that process of decomposition, transforming the chips in to nutrient-rich fodder for the garden.