As a rule no. Aside from being really ugly dyed mulches do not contain harmful substances and if any mulch does contain a "weed suppressant it must be labeled as having that. But then there is nothing to prevent someone from buying one of those and then forgetting it was a plant growth suppressant.

My neighbor buys it from a place that has huge piles of mulch and you buy it by the scoop full which they load into your pickup truck so I'm pretty sure it wouldn't have anything that would make it more expensive. That is the cheapest way to buy mulch. Thank you!

So a follow up question. I had a teenager start digging up the old mulch and there was more of the mulch than I thought, although its partially decomposed. I constructed a one foot high raised bed over a double dug area. Would it be OK to have about 1/3 of the bed mulch? It looks like it will end up being 2/3 soil on top of 1/3 of the mulch and decomposed mulch. I also have compost that I can put on the top of it. Since its around the trunk (and roots of the tree) will it be nutrient deprived soil? It looks really good - dark brown crumbly dirt.

i planted tomatoes kale and arugula in 3 -5 inches of dirt over woodchips, they did fine

thedarkness, did you add any nitrogen as they say to do? Or did you just pile on the woodchips?

I saw "Back to Eden," and it sounds so much like Ruth Stout's way...but I'm a little afraid of pure woodchips. Would love to hear what you did, if anything.

Mulches, to be effective, should be about 4 inches thick. That will limit the amount of sunlight anything trying to grow under that mulch so there would be no growth. There is some evidence that mulches much thicker than that might restrict air exchange to the soil, and little evidence that mulches thicker then 4 inches suppress growth any better.
Wood chip mulches have a very high Carbon to Nitrogen ratio, about 400 to 600 to 1, so digestion of them by the soil bacteria is very slow, usually. Working wood chips into the soil can cause the soil bacteria to go to work on digesting them which can cause them to use all the available Nitrogen while doing that. That causes a temporary loss of available N to the plants that might be growing there.
The wood chips used in the Back To Eden video were applied to the soil surface as mulch, not tilled into the soil.

Something "doing fine" is very subjective. So yes, I'd recommend adding additional N as is commonly recommended whenever wood chips are mixed in with the soil.

In theory if you could know for a fact that your soil was excessively high in N you could get by without adding it. But since that is difficult to document why take the risk when it is so easy to do.

It's the same principle one follows when adding lots of raw, uncomposted leaves to the soil.

Not to mention that layering components rather than mixing them creates its own set of problems.

Dave

Nitrogen availability in good organic soils is dependent on the activity of the Soil Food Web which feeds on that Nitrogen to convert the organic matter in soil into other plant nutrients as well as supply the plants growing there with a basic building block. The activity of the Soil Food Web is soil temperature dependent. Undigested organic matter in soil will cause the Soil Food Web to get to work on that and that can cause a temporary tie up of available Nitrogen to the detriment of growing plants. Putting compost into the soil, compost is already digested organic matter most of the time. will feed that Soil Food Web who will help convert that material into nutrients the plants can use. Putting undigested organic matter into the soil will cause those members of the Soil Food Web to expend all of their time and energy changing that undigested organic matter into something the plants trying to grow there can use. Putting undigested organic matter, ie. wood chips, on the soil will not much disturb the Soil Food Web in the soil, although when they have little else to do they will work on that material and slowly work it into the soil.

Here is a link that might be useful: Nitrogen in soil