July 26, 2020

Wonderful World of Wood Chips

Thibault - international visitor and
wood chip spreader extraordinaire

It's time for Jeopardy. 
  • The category is Soil
  • The answer is This readily available material improves most soils.
The question is, What are Wood Chips?

Twenty years ago, I ordered my first monster load of wood chips from FPL, our electric company. FPL is responsible for keeping their electrical lines clear. They remove vegetation, send it through the chipper, and deliver the resulting wood chips to customers free of charge. I planned to use the wood chips as a mulch, to cover bare ground. Mulch is wondrous. It can be made from more or less any organic material (and even inorganic material, but then it's not so wondrous). I had tried mulching with palm fronds, which seemed to fall in enough abundance that I was able to spread them out and cover the backyard. Unfortunately, the weeds zigzagged in and around the fronds, until they found some sunlight. The palm fronds simply made the weeds harder to pull up. With wood chips, I planned to spread them four to six inches deep. I wanted a thick layer of mulch to help keep moisture in the ground a little longer and to control the weeds. Over time, I hoped they would decompose and add some fertility to my scrawny soil. 

That was the sum total of my plan. Bring in wood chips, spread them, and wait. But my vision was much larger than that. Why is it that everything that most of us touch turns to waste in precious little time? Why aren't we building up the world around us and creating more abundance?
Decomposing nurse tree in a forest.
Photo credit: Jonny Hansson, cc
How is it that with no help from humanity, a forest grows up and supports a community of plants and animals? I wanted to grow such a forest, but one that would provide exotic/tropical fruit. And I wanted to do it all on a small suburban lot.

I had read some books put out by the Rodale Institute back in the 70's and 80's. I remembered a focus on composting, cover cropping, and building up the soil. One tidbit struck me and stuck with me. Since a wild forest supports a wealth of healthy trees, an orchardist would do best to emulate the processes at play in a natural forest ecosystem. In a natural system, trees grow, die, fall to the ground, and decompose. This lays the groundwork for new trees to replace the old ones. The decaying trees on the forest floor hold moisture far better than many soils. Tree decomposition unleashes nutrients that new trees need to grow. Left to their own devices, neither irrigations systems nor fertilizers nor pesticides need to be brought in.

With natural forest decomposition in mind, I considered employing some Scottish Highland caber tossers to heave some logs and tree trunks around the backyard. When it came down to it, FPL's offer to deliver a free load of wood chips seemed the safer choice. Wood chips would decompose faster than logs, due to their larger surface area. For the same reason, wood chips do not hold water as well. These differences notwithstanding, I was hoping that wood chips would provide a basis for the magic and health of a forest ecosystem.

After spreading several loads of wood chips from FPL, we had laid down a deep, massive layer of mulch. We waited for the decomposition to get going, before planting anything new. This is an important point. Had we been in a big hurry, we could have brought in some nice soil and created raised beds. In such a scenario, we would be robbing some other piece of the planet of their topsoil and transporting it some distance just to improve our own soil. This presented an unappealing intervention, from both environmental and ethical perspectives. Wood chips, on the other hand, are a local waste product. If they don't go into somebody's backyard, they would most likely end up in the landfill. Essentially, we would be growing soil from a waste product. Wood chips have significant environmental appeal, but they do require physical labor and patience. 

Our patience has paid off in the kitchen. Aged wood chip brownies are outstanding. Shredded wood chips make a great stand-in for hash browns. Talk about losing weight! Wood chip stew far surpasses stone soup in both flavor and consistency. Just having a little fun with you. Keep the wood chips out of the kitchen, unless you have thoroughly researched their use in your wood stove. 

In reality, I didn't anticipate all the benefits that would accrue from our patient and continued dalliance with wood chips. Once the first layer of mulch started to break down, I no longer had to worry about the decomposition temporarily robbing nitrogen from the soil. At that point, subsequent mulch additions are no longer in direct contact with the soil, but rather buffered by an already decomposing layer of wood chips. Extra wood chips can be used to cover an unsightly brush pile or scraggly undergrowth that you no longer want. In the short time it takes to cover it up, the unsightly morphs into the beautiful. Along the same lines, placing kitchen food scraps on the ground and covering them with wood chips is an easy composting method requiring no measuring, no turning, and no watering. As to the fun side of wood chips, energetic children of all ages can have a grand time running up and down a big hill of wood chips, before they are spread around.

Over time, the tilth of the topmost layer of soil improved. When I started importing local wood chips, I was unaware that until a hundred years ago, the land I live on did not exist; it was an underwater part of Sarasota Bay. Dredge and fill activities in the 1920s created Lido Key out of the Cerol Isles. I basically live on a giant shell mound covered with about a foot of mostly sand. This has implications for plants. For one thing, plant roots aren't able to take up the nutrients they need when growing in shells. For another, sand does not retain water needed by a plant's roots. Much to my delight, many of these problems can be ameliorated with the addition of large amounts of wood chips. 

A variety of mushrooms grow in wood chips
I can tell the mulch is decomposing. First off, it loses volume over time. Furthermore, I see a parade of mushrooms here and there for a day or two after a good strong rain following a dry spell. That tells me there is a mycelium network growing amid the wood chips. Recent science has shown that these fungal networks have a mutually beneficial relationship with woody plants. The fungi are more efficient at gathering water and nutrients from the soil than a plant's roots. I was hoping that, as the mulch decomposed, I would start seeing earthworms. Even after decades of wood chip application, I only see the occasional earthworm. For the first decade, the wood chips broke down slowly.  I didn't need to replace it too often. Then, out of the blue, we were invaded by wood-chip-eating millipedes. It would appear that instead of earthworms, we have millipedes. I do have to replace the wood chips more frequently now, but I take that as a positive sign.

Wood chips host millipedes and fungi 
How do you go about finding a good local source for wood chips? Before launching into this, if trees are not a dominant feature of your area; don't bother looking for wood chips. You won't find anyone looking to unload them. I started getting wood chips from FPL. Over the first few months, they delivered about six truckloads. They have not been back since. And not for lack of requests on my part. After that, I bought a small chipper. I figured I could chip up the many branches that fall to the ground and make my own wood chips. I encourage you not to go this route, unless you have a lot of storage space. The smaller chippers don't chip well and the more powerful chippers take up a lot of space. I moved on to local arborists and tree service companies. I called each company and whittled the list down to those who use chippers and who do tree work somewhere near my home. When I need mulch, I put out the call. This has worked well for me over the years. I haven't tried Chip Drop, but this looks like a promising option. Chip Drop is an online matchmaking service for those who wish to get rid of wood chips and those who want wood chips.

In writing this article, I was amazed to learn that many experts advise against the use of wood chips for mulch in a home landscape. Wood chips have brought life to our sandy and shell-packed backyard. Wood chips have helped create a verdant and edible mini food forest. So why are these experts kvetching about it? Linda Chalker-Scott has put together a fabulous website that addresses many horticultural myths, including some about wood chips. Science has only recently started sorting out the soil interactions between plants, fungi, bacteria, nutrients, and water. Since the science is incomplete, here is my non-scientific roundup of the issues raised and my responses. 

Issue or Myth: Wood chips may bring in termites or attract bad bugs
Response: I have never seen this happen. My limited experience with termites indicates they prefer large, old hunks of wood. That said, it does make sense to me to keep mulch away from your house to prevent moisture buildup. I keep mulch several feet away from all structures.

Issue or Myth: Wood chips acidify the soil
Response: I have alkaline soil, so I would consider this a plus, if it were true. I would bet that even if the wood chips start out acidic, decomposition would render them more neutral, and they would be further neutralized by the time they actually reach the soil.

Issue or Myth: Wood chips from diseased trees might bring diseases to your trees
Response: How would that work exactly? A top-dressing of wood chips would not touch the roots. It is important to keep wood chips well away from the trunk or main stem of a tree/plant, so pathogens wouldn't be transferred that way. The disease affected a living tree, so the disease would likely dissipate once the living tree is no longer there to play host. 

Issue or Myth: Wood chips will rob the soil of nitrogen needed by nearby plants
Response: Over the long term, the wood chips will increase fertility. In the short term, various experts seem to think the nitrogen-robbing zone is only at the soil surface, where the wood chips meet the soil. Most nearby plants are not pulling nitrogen from the soil surface, but rather through their roots, which should be planted and growing in the soil itself. This is probably a great area for scientific inquiry. Many folks are experimenting with burying partially decomposed wood chips, biochar, and what not.

Wood chips create fungal-dominated soil
Issue or Myth: Over time, wood chips create fungal-dominated rather than bacterial-dominated soil
Response: I would think this is true. Around trees, this works well for me. I grow occasional vegetables around my trees, and they don't seem to mind decomposed wood chips. 

Issue or Myth: Wood chips create problems for annual vegetable plants
Response: You can move the wood chips away from vegetable plants entirely, if you are worried about this. I generally wait for the wood chips to decompose, before planting vegetables. Be sure to plant your annuals in the soil and don't let the wood chips directly touch the plant. That said, if you have dedicated an entire area to annual vegetables, there is expert consensus to keep the wood chips in the pathways and not in the beds. I have no idea if this is truly important or just another gardening myth.

Issue or Myth: Wood chips don't kill underlying weeds
Response: Wood chips are most appropriately used to prevent weeds, so it's best to make sure the area is weed-free before you start. If you are looking to mulch a weedy area, consider covering with multiple layers of heavy cardboard first, before applying a deep layer of wood chips. 

Issue or Myth: You don't know what's in those wood chips
Response: I wouldn't buy wood chips from the store. You have no way of knowing whether it contains toxic chemicals or weed seeds. Perhaps they added artificial color to make it look nice. You may be getting construction debris. You may be depleting the soil of its nutrients where the tree was grown. These are all unknowns, when you buy from the store. Find a local source. Ask about the type of wood, whether it was treated with chemicals, or whether it was diseased in some way. Insider tip: don't accept mulch with any significant quantity of palm fronds, if you are planning to spread it manually with a fork. 

To my friends who live where wood chips are rare: Check with your local landfill. Where I live, the County puts out large bins of compost/mulch. If I wanted, I could drive up with a large container, fill it, and bring it home. Perhaps there is something similar where you live. Consider other mulch materials. When I lived in Massachusetts, I used a combination of summer's grass clippings and autumn's lawn-mowed leaves. What waste residues are produced in your area? There might be crop residue, livestock manure, brewer's waste, or coffee grounds. You may be able to combine waste products to create excellent mulch. These mulches may not provide the same fungal symbiosis that wood chips do, but they should still help suppress weeds, retain water, and improve soil tilth.

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