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Friday, February 15, 2013

Wood Chips, Good for Gardens?

Wood chips are in abundant supply across the Ozarks. From road crews and electric companies grinding up trees and limbs, it’s easy and tempting to use chipped wood in the garden. But if you choose to use wood chips, there are some cautions about how you do it.

Wood chips do an excellent job of blocking out sunlight, preventing weeds and holding in moisture. However, as the chips decompose and break down, they rob large amounts of nitrogen from the soil and can weaken or damage your plants. Additionally, some kinds of wood chips can damage the plants in other ways. You can’t always tell what kind of wood has been chipped, and if there’s walnut or cedar mixed in the chip pile, both of those contain natural growth retarding chemicals. (That’s why you don’t see weeds growing under cedar trees, for example).

The bigger issue, though, is the nitrogen robbing that fresh wood chips cause. It’s part of the decomposition process for the wood breaking down, but as a mulch, fresh wood chips are not good for garden plants.

A safer method for using wood chips is to let them compost for at least a year before applying them to the garden. Two years is even better as that allows for any cedar oils or walnut oil (known as juglone) to leach out of the wood. Then you can apply the rotted wood chips as a mulch or soil additive and not be in danger of robbing the nitrogen the plants need.

Much of the soil in my garden has been created from, or with, wood chips. My method 30 years ago was to haul in piles of fresh wood chips and spread them in pathways in my garden. The chips would remain there for 2 years, then I would till up the rotted chips, mix them with well-composted manure and build new raised beds. (In the photo above, I am now using gravel in my pathways as I no longer need to create new soil).

If you do choose to use wood chips around your shrubs, berries or vegetables, use chips that are at least a year or two old. Mix them, half and half, with composted horse, chicken or cow manure, as long as the manure has been composted at least a year, also. That will add some nitrogen but in levels safe enough for your garden plants.

Wood chips are an excellent source for building new soil for beds. If mixed with manure and left to rot for 18 - 24 months, then tilled into existing soil, it can help the soil hold moisture and add fertility. Just be aware that if you use freshly chopped wood chips on the garden, you are likely to have weakened plants, slow growth, lots of fungal problems in the mulch and possibly even dead plants. Always use caution when using fresh wood chips around plants.

Copyright 2013 Jim Long

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