2/15/2013

Wood Chips, are they good for your garden?


Wood chips are in abundant supply. 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 now use gravel in my pathways since I'm not wanting to create more 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 can be 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.

3 comments:

Comfrey Cottages said...

thank you for sharing your wisdom about wood chips, Jim. I had doubts this year when a friend was covering her entire veg garden with chips.. she was getting them at the city yard waste dump.. I am glad you highlighted the wood types that could actually be included and the reasons they wouldn't be beneficial. Nice share about letting it age and adding manure and other compost to it before use. I will share this post with her! thanks! Leslie xx

Ben Lannoy said...

Nice post Jim. We're just in the process of ordering some in for a huge bed for a client. I only found out recently that it also helps to stop seeds from penetrating the soil from above. If done thick enough it works a treat for all of the reasons you highlight, especially in hotter climates. All the best, Ben

Alastair Dodwell said...

Your Wood Chip blog is Nice looking...