Science Wednesday! Dyed mulch vs natural: which is better?

There are natural mulches on the market and there are dyed mulches. Which are better? Is there a health risk with dyed mulch? These are all questions I get asked, and that I see online.

MulchTub

Let’s start by talking about where mulch comes from. Typically your shredded wood products are either forest products – trees taken down by people clearing land or felled by tree services, branches and such like from tree trimming jobs – or waste wood like pallets and cast-off building materials. These materials are brought to a tub grinder and chewed up into the luscious, woody product we know as shredded mulch. Check out the video below to listen to soft piano jazz while a massive metal beast turns wood to mulch.

This mulch product then may be pushed into big long piles where it’s allowed to season a bit, or it may be dyed. The conventional wisdom is that commonly it’s the pallet-derived mulch that’s dyed. This is done to conceal the fact that it’s less desirable wood (I can’t personally confirm this). The dye colors most commonly used are black, brown, and red.

Is dyed mulch dangerous?

Short answer – probably not to people, but still exercise caution when handling. Red and brown mulches are dyed with vegetable dyes. Black mulch is typically dyed with carbon black. Carbon black (wikipedia link because all the citations are there) ” is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar,ethylene cracking tar, and a small amount from vegetable oil.” (from the previously mentioned wikipedia entry). Doesn’t sound awesome and there have been studies linking it to cancer, but they seem to point to it as an inhaled carcinogen. I don’t know if that means it’s less of an issue once it’s in place, but that’s my takeaway.

dyed mulch

Dangerous to plants? Probably not because of the dyes. I’ve read the concern that fresh wood mulch that hasn’t broken down yet will rob the soil of nitrogen but we’ve thoroughly debunked THAT load of BS here. Right? Right. The only real danger I can see is that if, in fact, the mulch is derived from pallets and random building materials there *might* be chemicals that would impact your plants. But I can’t say that it’s universally a problem (or not) because they don’t put a sticker on your bag of mulch telling you the source and the species of woods you’re getting.

However that doesn’t change the fact that…

I do believe dyed mulches are the devil

Why? Because I’m a design snob. This is no secret. Red mulch? Ornamental grasses surrounded by red mulch look like cheap hair plugs in Ronald McDonald’s scalp. Black mulch draws the eye and looks like you planted in the aftermath of a forest fire. The focus of your landscaped beds should be the plants. Not the mulch.

There’s also the fact that the dyes aren’t completely locked into the product. Every time we have a big storm forecast, I get an email from the local mulch producer, warning us that if we recently installed dyed mulches we need to tell our clients to immediately hose off any dyes that ran off onto adjacent sidewalks and patios. I have enough to worry about without having to freak out that my mulch color is going to run everywhere like an audience member’s mascara in the first 20 minutes of Pixar’s UP!

So which is objectively “better”? You know that I prefer to base my opinions on science, and I’m not finding compelling research either way. But shredded hardwood mulch without dyes has had less done to it than dyed mulch, it doesn’t bleed dye all over my driveway, and it doesn’t stand out with ugly, unnatural colors. I’ll let you decide (but I may snark about it if you choose wrong).

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