Is dyed mulch good for my garden?

Updated: Sep 14

A few years ago, I always used black dyed mulch. It looked so good in my plant beds and the color lasted from spring to late fall. It covered my soil and looked great, so why is it so low on my list now?


First, a dyed mulch can introduce harmful chemicals to a soil that hurts plants and the living things that a great garden needs—things like soil microbes, worms, and small insects. Second, the wood sources for dyed mulch aren't sustainable. Third, it’s possible that the wood will tie up nutrients from your soil, taking them away from plants. A lack of sustainability and the potential of harmful chemicals mean that they are crossed off my list as a good mulch.


Dyed mulches can introduce chemicals that are harmful to our plants. The best dyed mulches are made using white wood that is porous. This allows the color to really pop and the dyed color lasts a long time--the two most important things for an aesthetically pretty dyed mulch.


In our local area, we have a lot of shipping and construction to support the greater Washington-D.C. population and its growth. Since the U.S. doesn’t want insect stowaways on incoming ships, wooden pallets and crates can be treated with an insecticide. Local construction projects often tear down old decks, homes, and other wooden structures—("recycled") wood sources that can contain lead paint, arsenate, or other potentially harmful contaminants. All of these chemicals are bad for the plants and the microbial life that are needed in a healthy soil.


The vast majority the dyed mulch in our area is made from white wood. Some of this wood comes from shipping and construction (a bad source); some comes from separating white wood during land clearing. It can be hard to find out the true source of wood from a company since the person answering the phone many not have a complete understanding. Either way, neither are a sustainable source.


For a brief period in summer and early fall, the white wood is used up and many of the local, bulk dyed mulches are made from yard debris (its rare that any of the natural wood dyed mulch is bagged). While yard debris is a better mulch material for your garden, it hasn’t been cured and it doesn’t hold its color well.


Overall, because it can contain harmful chemicals and the best wood sources aren't sustainable, dye mulch no longer finds a home in my garden.


But if that isn't enough, there is some debate about whether a dyed mulch takes nutrients from your soil. I’ll explore both arguments.


Argument for dyed mulches taking nitrogen out of your soil:

The best mulches are cured—a process that ages wood for a period of time before its sold. During the curing process, the wood hits hot temperatures to kill weed seeds and start breaking down (decomposing) the wood.


Dyed mulch, however, has to be freshly cut (uncured) so that the dye will stick to the wood. When the dyed mulch is then applied to a garden, it has to start the decomposition process and will take nitrogen out of your soil to do this. If you’re applying mulch in the spring, the mulch pulls the nitrogen out of the soil (and away from your plants) just as your plants need it the most to grow.


If enough time passes, the dyed mulch will break down far enough, and return the nitrogen and other nutrients to your soil. If you’re like most gardeners, however, who replace their mulch by taking off the old and putting down new, then you are usually taking away the dyed mulch before it has returned the nutrients. Effectively, this is just taking nitrogen out of your soil over and over again.


This argument is what I come across most frequently online and from long-term industry professionals.


Argument against dyed mulches taking nitrogen out of your soil:

Dyed mulch is fresh, or uncured, but it doesn’t tie up nutrients from your garden soil, or at least in a way that hurts plant growth. Because the mulch is placed on top of your soil, the vast majority of the mulch has no contact with the topsoil and so can’t pull the nitrogen up and out of the soil, or at least in a quantity that stunts plant growth.


I come across this argument much less but in some blogs that I trust and at least part of its logic makes sense to me.


Since I’ve explored two different views on dyed mulches, I’ll give some takeaways that I think relatively straight-forward.


Summary:

  • Dyed mulch wood sources are not sustainable and there is a risk that it contains harmful chemicals that hurt plants. There are a number of healthy and sustainable mulch options that are better to use: see our upcoming post, "What's the best type of mulch?"

  • Dyed mulches are not cured. Even if they are sourced from materials that are chemical-free, there is a risk of introducing weeds or other unwanted seeds to a garden.

  • Uncured mulches—dyed mulch or not—should never be tilled into a soil; both arguments for and against dyed mulch agree.


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