Wood Chips for Mulch – Answering a Reader’s Question

Steve, a reader in Lubersac, France, emailed me to ask if I envisioned any problems using willow tree residue (that has been shredded) as mulch.

Willow for firewood is Steve’s main source of heating and hot water. He’s just starting to harvest his first crop of willow and is left with all the thin straggly bits, except for the ones chosen to start new trees. He explained that the residue is a considerable amount.

The local town hall there has recently embraced a ban on bonfires to cut down on pollution. (This might be admirable except for the fact that a farmer can still burn all his rubbish including plastic seed and fertilizer sacks!)

Steve would have burned his residue had the ban not been put into effect.

Sad that lots of folks burn or trash great organic material, including leaves, that could be recycled to make their gardens even better and more productive. They just don’t realize how valuable these materials are to their garden!

Wood Chips

I would define wood chips as any wood that has been shredded in some manner.

Primary Concern About Using Wood Chips for Mulch

The primary concern about using wood chips for mulch is that the newly shredded wood may cause soil life to use available nitrogen in the soil to break down the wood chips, rather than making it available for any crops that are growing.

And that’s the thing you want to avoid. By testing your plan in a small area rather than on a large scale, you should be able to prevent any major problems.

The Other Concern that Comes to Mind

The only other concern I can think of is if the wood chips are from any species of the walnut family (for example: black walnut, hickories, pecan, butternut) which produces juglone in the soil where it grows and within about a 50 foot radius of the dripline. This substance can kill plants like tomatoes, peppers, potatoes and eggplant. Not all plants are sensitive and thus not damaged. Corn, beans, beets, carrots and onions are tolerant of the juglone, as are most trees, shrubs, annuals, and perennials.

Fortunately, even leaves and shredded wood of these trees can be used if composted or aged long enough to allow enough time for air, water and bacteria to break down the juglone and render it harmless. (For the leaves I’d age or compost at least a month and for their wood chips I’d recommend at least 6 months or more to be safe.)

Be Safe – Go Slowly – Test

Over the years wood chips have always been one of my favorite mulches and I have used them with great success.  In spite of that, since there are always so many variables from one garden to the next, I would recommend moving slowly and “test” before you do anything on a large scale.

As Mulch on Top of the Soil – Your Safest Bet

If you use wood chips on top of the soil, it is highly unlikely that you would experience any adverse effects.  Test a spot anyway just to be safe.

Incorporating into the Soil where Crops are Growing – May Cause Problems

If you turn the wood chips into the soil, you just may experience problems if you have crops growing in the same soil while the wood chips are decaying.  The soil life will work on breaking down the chips and they use nitrogen to do it.  Therefore, the need for nitrogen by any crops growing in that soil will be neglected until the chips are broken down.

My Experience With Wood Chips

Years ago, before I knew anything about nitrogen and how soil life worked, I dug many a wheelbarrow of wood chips into garden beds.  I had no adverse effects, in spite of the fact that the people who sold us the chips warned us about it.

Not sure why they never had an effect on the other plants.  Maybe they were aged enough.

Since we could get a dump-truck load of chips for only $20, we always kept at least one big pile of chips.

Here are my favorite uses:

• After digging out about 6 inches of rich soil from my garden paths and tossing it up onto my garden beds, we’d fill up the paths with wood chips, making it level with the beds.  After a year or two the chips turned to black soil.  Then we’d dig  out the paths again and toss it onto the beds and refill the paths with new chips.

• Edging all the gardens and borders with a heavy (almost a foot deep) layer of chips.  This kept the grass from edging into the beds and when it started into the mulch it was easy to pull out.

• Mulched all my flowers borders with it.

• Mulched a lot of my garden beds with it.

• Incorporated it into any new beds being created.

No Chipper/Shredder

I don’t have a chipper/shredder but I still try to keep as much debris from pruning as I can.

For example: when I trim my back-side border hedges each year, I cut most of the limbs into 4 to 6 inch pieces and leave them where they fall to serve as a mulch for those borders.  It’s not shredded as I would prefer, but it works and the pieces eventually decay and recycle to feed any plants in that border.

Final Thoughts

Any wood you can shred and use – do it!

Over the years Steve’s debris from the willow harvest will save him lots of money that he may otherwise spend obtaining mulch from other places.

There is always a time and place that a gardener may prefer straw or some other mulch rather than wood chips on certain beds.  But for the most part, the wood chips  will get the job done without his spending money on some other form of mulch.

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