It’s springtime, and after a long winter where the wood mulch protected the food web in your soil and biodegraded, it’s time to freshen it up for the new growing season. But what are you supposed to do with the old mulch?
You can put natural, untreated wood mulch in your yard waste bin or in a compost bin, you can also compost it in place or in a home compost. Dyed and treated wood mulch does not compost well and may contain toxic CCA. Do not put dyed mulch in a yard waste bin or compost. Instead, check your municipality’s policy for how to dispose.
Is Mulch Considered Yard Waste?
Yard waste is any vegetative organic material that’s produced through yard or garden maintenance. So long as your mulch is natural, untreated, biodegradable vegetative matter such as wood chips and bark, then it’s yard waste.
However, plastic mulches like landscape fabric and tarps, and dyed mulch are NOT yard waste and you should not add them to yard waste bins.
Can I Put Mulch in My Yard Waste Bin?
Yes, you can add most natural, untreated mulches into your yard waste bin or even a compost bin — and your municipality may even require you to instead of putting it in the garbage. Yard waste is then composted and turned into topsoil for building projects or compost.
When you put yard waste into the garbage, it:
- Takes up a ton of space in landfills. In fact, yard waste comprises up to 10% of all household waste.
- Adds greenhouse gas emissions from organic matter breaking down in anaerobic conditions or doesn’t break down at all. Organic matter needs oxygen to degrade and being buried under a ton of plastic trash does not allow it to breathe.
- Wastes precious natural nutrients that could fertilise your garden and lawn and replace the use of synthetic fertilisers.
However, if you’re not using natural mulch, check with your municipal waste management facility on whether they can recycle it or to bring it to the facility for disposal. You shouldn’t put anything in a yard waste or compost bin you wouldn’t add to your own compost (i.e. treated wood, plastic, non-organic materials).
How to Naturally Dispose of Wood Mulch
The best way to dispose of untreated wood mulch naturally is by composting.
I know, I know! So many gardeners warn against composting wood chips as it ties up nitrogen to aid it in breaking down. That is true. However, there are a few ways to mitigate this:
- Add more high-nitrogen sources to your compost bin. Usually, you’d want to keep your carbon to nitrogen ratio to 30:1. But since decaying wood ties up nitrogen, you can add more nitrogen to balance things out. Add more fresh grass clippings, blood meal, alfalfa meal, and spent coffee grounds.
- If the mulch is around shrubs and trees with deeper roots, you can let the wood mulch decay in place. The lack of nitrogen only affects the upper layer, while a tree’s deeper roots can reach nitrogen deeper in the soil. You can also add a nitrogen source like in composting before adding a fresh layer of mulch.
Can I Lay New Mulch Over Old Mulch?
Yes, you can lay new mulch over old mulch, so long as the mulch is from a natural source and untreated/undyed. The old mulch will break down under the new mulch, returning the nutrients into the soil.
As I mentioned above, decaying wood chips can tie up nitrogen, so you’ll want to add a high-nitrogen source, especially if it’s in garden beds where the roots are shorter.
However, you should remove the old mulch if:
- The old mulch is matting (congealing to become one layer). Matted mulch will prevent rain and oxygen from reaching the soil and causing anaerobic conditions in which fungal diseases will take over.
- The old mulch is already 2 or 3 inches thick as you don’t need to add new mulch unless it’s for the sake of appearance. In that case, you’ll want to remove some mulch so you can add enough new mulch to cover the old while ensuring it’s not too thick for any garden plants.
How to Dispose of Dyed Mulch?
Check with your municipal guidelines on what to do with dyed mulch. Dyed mulch cannot be composted or added to your yard waste bin. You may need to bag up the dyed mulch and take it directly to your waste management facility where they’ll dispose of it.
Dyed mulch may be toxic, depending on what was used to dye it and where they sourced it from. Quality brands of dyed mulch will use harmless dyes like iron oxide-based or carbon-based dyes, but cheaper brands will use toxic chemicals for dye.
Dyed mulches are made from recycled wood. Seems like it’s good for the planet, but the recycled wood (especially from construction and demolition) could contain chromated copper arsenate (CCA). CCA was used for decades to pressure-treat wood. CCA is harmful to you, animals, the food soil web, and young plants. You don’t want it in your yard.
Even if it doesn’t contain CCA, the recycled wood is treated to prevent it from biodegrading, which means you can’t compost it. It’s best to avoid dyed mulch and go with wood chips, which are cheaper and healthier for your soil and look nicer.
The best way to dispose of old, untreated wood mulch is to use it as compost. Just add more nitrogen to compensate. Dyed mulch is best avoided, but if you already have it, you’ll need to dispose of it by taking it to your local waste management facility.