Wood chips are an excellent soil amendment – if you add them in the right way. If you add them incorrectly, they can actually cause nutrient limitations in your soil for a while. The benefits of wood chips added to soil are huge – but you have to add them the right way. Let’s explore how to do this.
What Is In A Wood Chip?
In the past, three to four decades technologies to convert trees, shrubs, and other plant waste into wood chips have proliferated. Companies clearing lawns, the edges of roads, logging companies, and various other sources produce huge quantities of wood chips. Wood chips consist of small pieces of a tree. Consequently, they mainly comprise wood, and may also have a bit of bark and occasionally a leaf or two mixed in there.
Most wood consists of a mixture of cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are relatively easy compounds to degrade and many simple fungi and even bacteria can degrade these. Lignin on the other hand is a really complicated molecule, and its degradation takes time and specialized enzymes from a handful of specialized fungi. Fresh wet wood also contains sugars and proteins and other simple carbohydrates.
What Happens When Wood Chips Break Down?
When a wood chip is made, it contains spores from the natural environment. Fungal and bacterial spores live on the bark of trees. As the chipper breaks these pieces of wood into chips, the spores spread over the chip. It is a bit of a mix and match, and we cannot predict what will be there – but we know there will be bacteria, yeast, simple fungi (molds), complicated fungi (the ones that make mushrooms) among other microbes present on the bark of the tree.
When you mix wood chips into soil, the fungi, yeast, and bacteria begin to grow into the wood chips using up these nutrients. As these microbes grow, they require nitrogen, phosphate, and other nutrients to grow – they will remove this from the soil and localize it into the wood where they are very active. This means that as wood chips break down, they can initially actually reduce nutrient availability in the soil.
One of the benefits of wood chips added to soil is that the chips undergo a series of cycles of being broken down by different microbes. Initially, fast-growing Trichoderma and similar species will penetrate the chips and break down the easiest to utilize nutrients. These microbes will be followed by slower-growing complex mushroom fungi that will target cellulose, hemicellulose, and eventually even slower-growing mushrooms that produce really complex enzymes that can release energy from lignin.
One of my favorite brown rot fungi is the chicken of the woods fungus. This sometimes comes up on logs I leave near my paths in the garden. This specimen is on a tree in a field near my garden.
Chicken of the woods being fried on my wood stove with some garden veggies. This is an incredible fungus that tastes like chicken – it really does! It turns logs into lovely little square cubes that bring magic to your soil.
The cellulose and hemicellulose degrading microbes tend to leave the lignin – this can leave a brown type of wood color – hence their name brown rot fungi. These are common in colder climates. One of my favorites is the chicken of the woods fungus.
We also get a different class of cellulose and hemicellulose degrading fungi – the soft rot fungi. These fungi are common in the soils of a healthy garden – they use a combination of abundant moisture and nitrogen from manure and the wood to rapidly degrade the wood.
I make my own spawn of Callocybe indica spawn. This is an excellent warm-weather fungus to help degrade wood chips and garden waste. You can buy grey oyster mushroom spawn such as this and incorporate this into your wood chips. It will take hold and grow. This is a tough mushroom strain. I have these in my garden too. If you can find a person who grows mushrooms ask for some of their old grow bags to put into your garden.
White rot fungi are fungi that can degrade cellulose, hemicellulose, and lignin. In order to degrade lignin, they use very complex and powerful enzymes. If we are to use a military metaphor, the brown and soft rot fungi are the light infantry – the white-rot fungi are the heavy guns. These fungi mean business – they may take some time, but they turn wood chips into the best compost imaginable.
How To Use Wood Chips In Your Garden
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Do Not Put It Directly Into The Soil
I find that if you incorporate fresh wood chips directly into your soil you will most definitely inhibit the growth of your plants. You may actually end up with no growth at all. One year an Erythrina tree blew over in my garden and the insurance company came and ground the tree up into wood chips. I ended up with about three tons of wood chips. I rotavated these into my soil, thinking that Erythrina wood is very soft and contains little lignin. It is really just fibers.
I ended up with an incredible overgrowth of Coprinopsis mushrooms. The soil became very very hot, and the fungi used up all the nitrogen in the soil. The maize that I had planted in this soil produced a very poor crop, and the bean and mushroom crops were not much better (I always plant the three at the same time). After this, I spoke to a few mushroom growers and gardeners and developed my own method to bypass this problem.
If You Need To Incorporate Wood Chips In The Soil, Allow Them To “Compost” For A Year First
I found a spot where a lot of wood chips get dumped in an old quarry. These chips turn brown after a year due to the action of brown rot fungi. After they turn this color, I find they are fine to incorporate directly into the soil or to use as a mulch.
You can see these partially brown rotted wood chips are an excellent mulch in my vegetable garden.
This shows the same crops a month or so later. Note there are no signs of nutrient deficiency (yellowing) in the maize or bean leaves and there are also no weeds.
This shows the soil after the crop when I rotavated the chips into the soil and then added manure between ridges to add additional nutrients to replenish the soil. The soil is very vibrant, the plants are healthy and the taste of the product is superior to what most gardens produce tastes like.
I use a consortium of wild and introduced mushrooms to break down my wood chips now. These mushrooms just keep growing and have built up a spore bank. I either get wood chips that have been stacked in a heap for a year or, if I make my own wood chips, I will place them on my footpaths for a year. The footpaths become active mushroom beds, and every now and then I get a nice crop of pink oysters or king oyster mushrooms. I also buy old mushroom soil from mushroom farms, and introduce this into the footpaths, leading to occasional flushes of button mushrooms.
A few pink oysters and lions mane mushrooms came up on the edge of my footpaths in my garden. The lion’s mane tends to grow out of small logs/sticks that you incorporate into your footpaths together with the wood chips. The pink oysters just pop up wherever they feel like doing so.
After the second year, ridge your soil and place the wood chips in the trenches between ridges. Place manure and leaf litter over the wood chips. Plant the plants on the ridges. This generates a significant amount of heat and warms the soil up, allowing great crops of early squash and maize.
In the third year, you can then take the compost that is between the ridges, and the soil, and mix these together. You will have rich soil that has leftover humic compounds from the wood, nutrients, and leftover microbial life. This makes the richest most amazing soil for your garden and actively increases the carbon content of the soil. This in turn increases the health of the roots of your plants and gives you better tasting garden produce.
Benefits Of Wood Chips Added To Soil As A Top Dressing
Over the years I have experimented with adding wood chips as mulch. This appears to not cause as much depletion of soil nutrients in the first year, and I have had perfectly adequate crops using wood chips as a mulch. Interestingly, using this method I have also noted I sometimes get small flushes of the ethnopharmacolically intriguing species Psilocybe azurescens that pop up after cold spells going into autumn. My ducks and chickens love these mushrooms and after consuming them spend hours just watching the banana trees blowing in the wind.
I hope this article has helped you understand the benefits of wood chips added to the soil. If you follow the methods I suggest above, you will find you get very healthy soil, a lot of bonus mushrooms, and a lot fewer weeds. Win-win all round. Share if you enjoyed the article.
Can you put wood chips under soil?
You can - if the chips are fresh, this may result in fungi absorbing nutrients from the soil temporarily while they degrade the wood chips. After this process is finished, the nutrients will be released back into the soil. This can however lead to failed crops - I prefer to compost the wood chips for a year, or let them age on the footpaths in the garden. This allows you to get the benefits of the chips without having crop issues.
Do wood chips make good compost?
In my opinion, they make the best compost! After three to four years, wood chips break down into a dark humic substance rich material that makes your plants disease resistant. This also holds moisture, nourishes soil microbes and just makes your soil amazing. Vegetables grown in this compost just taste better.
Are wood chips good for a garden?
Yes. They are an excellent mulch, and as they break down they release nutrients and build up soil carbon. This is important for soil fertility.
Can I put topsoil over wood chips?
I find that with clay soils you can. Dont put too many chips - a two inch thick layer will work. If your soil is rich, and you add a bit manure you should not end up with too much nutrient being taken away from the plants by the fungi that grow in the chips. If you put a thicker layer, the fungi will temporarily strip the soil of nutrients, and then release these nutrients again once they are finished degrading the wood chips. This can give you one bad crop followed by an excellent crop. I prefer to weather the wood chips for a year to avoid these cycles.