Things to Know About Using Woodchips and Leaves in the Garden

If you are a gardener you have probably heard people talking about how great woodchips are. That is probably because they are a very good resource for building up organic matter. Woodchips and leaves are also very easy to acquire and and best of all cheap! Woodchips do have a few drawbacks but if you are aware of those you can easily work around them.

How to Find Wood Chips

Woodchips (and large quantities of leaves) are not hard to find. With storm damage or people removing trees (especially one’s like Bradford pear trees <- PLEASE REMOVE THEM!) there are usually plenty of people in any given area trimming up and chopping up trees nearby. My latest mountain of woodchips came as a result of two sources. One was a company called Chipdrop. Chipdrop is a free way to get woodchips. You simply sign up and specify what you are willing to accept and give any special instructions. If a chipper truck is in your area you may get a load of them. It isn’t a guarantee and offering to tip a little for the delivery may help induce a driver to bring you a truck load.

The other way is to simply directly contact a lawn or trimming service. They can then bring it directly to you to drop off at your property. It benefits you in that you can get the woodchips but also may help the chipper if they are close by because they may need to dump several loads and it may shorten the travel time and fuel costs spent in transporting the wood chips. It’s a win win situation for the tree trimmer and the gardener!

What to Know About Woodchips and Nitrogen

Since the trees the woodchips came from are fresh you need to be careful in how you use them. Or at least be careful about using them right off the bat. Woodchips are a big source of carbon which is considered a brown compost material. In order for microbes to break down carbon they need nitrogen or green materials. If woodchips are laid directly on garden soil they will pull nitrogen from the soil. The microbes take the nitrogen and temporarily will use them to help break down the woodchips. This is called immobilization. Once the woodchips break down the nitrogen returns back into the soil and the plants can use it again. Time is on your side! If you don’t need to use the woodchips right away there’s nothing wrong with letting them sit and break down on their own.

Leaves are also a brown material and can be used in the same way as woodchips. If the leaves are full sized try to break them down further with a lawnmower or woodchipper. The smaller the surface area of the leaf the faster the microbes break down.

How to Use Woodchips in the Garden

Let’s talk a little now about how to use woodchips in the garden. Because of nitrogen immobilization there are some ways you can use them right away and others which would be best to give them some time.

Immediate Use of Woodchips

If you want to put mulch down for pathways or mulch around mature trees woodchips may be just the thing. Nitrogen isn’t an issue at all if you are just wanting a place to walk that is clear of the weeds. In case it may help reduce weeds in two ways:

1. The woodchips cover the soil and prevent seed germination.
2. Weeds get sapped of nitrogen and can’t grow as vigorously. Plus they are shrouded in darkness!

Uses Where you Should Wait on Woodchips

If you are wanting to use woodchips in the vegetable garden, around annuals, or perennials give the pile some time to break down. These plants can be impacted by the nitrogen immobilization and won’t perform as well. What a lot of people do is lay down woodchips for pathways. Then at the end of the season the gardener can toss the woodchips into the raised beds and replace with fresh woodchips. It’s a cycle that can be sustained year after year.

If you are planning on using them for a filler in raised beds make sure you have some time for them to break down. Mix them together with high nitrogen fertilizers like blood meal, alfalfa meal, fish meal, or manures.

Fresh grass clippings are also excellent to use to help balance the brown materials in the woodchips. I like to use a bagging lawnmower then dump the grass clippings into the woodchips. Then mix them up a little into the top layers of the raised beds.

Another option is to create a lasagna garden, also known as sheet composting, by using a mixture of grass clippings, woodchips, and leaves. Create layers of materials while alternating green and brown materials. It may help to place a layer of cardboard or newspaper on the soil surface first before putting down the organic matter. The material will break down over time but it will slow the weed growth underneath it.

The Compost Bin is Always an Option

Putting the woodchips in a compost bin with kitchen waste, manures, grass clippings, yard waste, and other organic matter is a great way to produce large quantities of compost. It will take some time but if you tend the pile, continue to add organic matter, and flip the materials to oxygenate the pile you will see some good results! Once the pile has cooled and broken down into smaller parts you can use it to top dress the garden beds.

Other Concerns with Woodchips

There are some other concerns to be mindful of when using woodchips. You may not know where the chips came from. The trees may have been sprayed as some point with herbicides and that can transfer over to your garden. Typically those will fade away over time and the likelihood of having a huge amount of herbicide in the woodchips I believe is on the low side but it is possible.

Certain species of trees may contain chemicals like juglones which are growth inhibitors. Walnut trees are one species than can have juglones. The can prevent many other species of plants growing around them from growing. This chemical can be conveyed to your garden. I recommend asking your chipper person if they know where the trees came from and what type they were. My woodchips were actually from Bradford pear trees which are rarely sprayed and shouldn’t have a concern with juglones.

Insects can be attracted to the wood chip piles. Termites and wood eating insects may be attracted to piles of woodchips so keep the piles away from important structures.

Check out this video for more on Using Woodchips in the Garden