Four or five years ago, we had to have a tree in our yard cut down. We asked the arborist to chip the smaller branches, and we used those chips to mulch the paths in our raised bed garden. A year later, we discovered the documentary, Back to Eden, about Paul Gautschi and his method of wood chip gardening.
We were intrigued, and as I looked at the paths in our garden I noticed that as the chips were decomposing, the soil was becoming black and gorgeous. We’ve been mulching our garden with hay, leaves, and grass clippings for many years, but thought that it might be worth experimenting with wood chips.
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We’ve had some amazing results, as well as some dismal failures. Here’s some of what we’ve learned.
First let me say while I am a firm believer in the benefits of mulch in a vegetable garden, I don’t think that any one method is the end all, or right for everyone. The best mulch that you can use is the one that is available in your area for free, if possible.
For us, wood chips, and grass clippings and leaves from our own yard, are available for free. We can often find spoiled hay relatively inexpensively, or even free. We use them all. By the way, here’s why I use hay, and not straw in my garden.
I wanted to discuss wood chip gardening because somehow it seems to have become a controversial topic online. Even some of my favorite bloggers are dismissing it. Often, the people who are disparaging it have not tried it, or as you read how they are using it, are using it incorrectly. I will say this from our experience – of all the mulches we’ve used, wood chips are the least forgiving. They need to be used properly, or can cause disaster.
What’s Being Said
1. Wood Chips Rob the Soil of Nitrogen
It is true that there is a nitrogen deficiency at the point where mulch and soil meet. It is important to plant below this level. Wood chips should not be dug into the garden for this reason, but only used as a mulch. I personally like to use a high nitrogen amendment like blood meal just below the mulch. Source.
TIP: if you are able to get wood chips that include branches with green leaves, those leaves are also a nitrogen source.
According to a 1971 Cornell bulletin, a 15 year study using wood chips was conducted on a farm in NY. In some areas, wood chips were applied as a mulch, in others, the wood chips were plowed under. Other test areas included traditional methods of farming and using cover crops. Over time, nitrogen levels in the soil increased in the areas where wood chips were used as a mulch. Source.
2. Perennials Prefer a Fungal Dominated Soil Which Wood Chips Provide, But Annuals Prefer a Bacteria Dominated Soil
When I read this, I contacted Dr. Linda Chalker-Scott, horticulturist and professor at Oregon State University. Here’s what she had to say:
I don’t buy the “annuals prefer bacteria, perennials prefer fungi” mantra, since I’ve seen nothing in published literature to support it. In fact, it’s well known that many annuals, including vegetable crops, are mycorrhizal, so I think this whole “bacterial soils for vegetables” thing is bunk. Basically, all non-grass species are mycorrhizal.
3. Wood Chips Will Acidify the Soil
As the wood chips are decomposing, the ph of the chips may be acidic. This won’t affect the soil below the mulch, and once the wood chips decompose, the soil it produces will not be acidic. There is no scientific research to support the idea that mulches such as wood chips affect soil pH. Source.
Our Problems with Wood Chips
Yes, we have had problems in our wood chip gardens. In every case, however, we were the problem, not the wood chips themselves. As I mentioned, wood chips as a mulch are not as forgiving as say, hay.
Mulch too deeply with hay, and you won’t likely have any problems. Maybe your soil won’t warm as quickly in the spring, or you’ll have a problem with slugs in a particularly rainy year.
No matter what mulch you use in a no-dig garden, it will need to be pushed aside at planting time so that you can plant your seeds, or seedlings in the soil, not in the mulch. Deep wood chips are very difficult to push aside. Not so with hay. Hay, of course, needs to be replenished much more quickly than wood chips and for us, often comes with a dollar sign attached.
I have found that 2 – 3″ is just right for wood chip mulch. Most of our problems have resulted from mulching too deeply.
In addition, according to this source, “wood chips that heat up and partially decompose can produce volatile organic compounds that inhibit seed germination and plant growth.” I have found that to be true. Seeds, especially small ones, that have planted in the layer just between the soil and the mulch (partially decomposed chips) don’t germinate. This can be a plus, since weed seeds also don’t germinate.
Plants That Have LOVED Wood Chips
We have found that all seedlings have done just fine, planted in the soil below wood chips. Also, any larger seeds that are not spaced closely seem to love the chips. For us, it has been too difficult to push all of the chips away for seeds that are closely spaced, like carrots. Squash does particularly well in wood chips.
And Those That Haven’t
Our carrots, beets, spinach and onions have not done well in our wood chip garden. In all cases, I suspect I did not move the mulch enough and planted in mulch rather than in soil. Mike planted some onion sets around our apple trees a few weeks ago, in a wood chip garden. He was particularly careful to plant them in soil. We’ll see how it goes.
I suspect that as the years pass and our wood chips fully decompose, planting small seeds like carrots will not be a problem. In the meantime, I keep some beds mulched only with hay or leaves, and plant these types of seeds in those beds.
I think that the beginning can be the hardest for this type of garden. The mulch is not yet decomposed, providing the soil with its rich store of nutrients. Paul Gautschi has been gardening this way for over 30 years. His soil is rich and deep. In the 15 year study I mentioned earlier, yields, in general, were highest in the plots that were mulched with wood chips. The method clearly works.
My Method of Wood Chip Gardening
It is generally recommended when starting a new wood chip garden to layer a few inches of compost on top of newspaper, and then a few inches of wood chips on top of that. Seeds and seedlings are then planted in the compost layer.
I’ve mulled this over quite a bit and have come up with a method that solves some of the beginner problems and provides a richer base for planting. I have basically combined lasagna gardening with wood chip gardening, and have detailed that method in my eBook, The Art of Gardening: Building Your Soil.
What’s your experience with wood chip gardening? I’d love to hear about it in the comments.