Moldy smelling bark mulch

[Don Peters]

I've been using bark mulch in my yard plantings for over 35 years. I've used it for a variety of practical reasons: looks, moisture retention, weed control, and erosion control. But another reason is that I simply enjoy handling it and putting it down. In fact, I often use both hands to grab a bunch of it, and then smell it before I place it. I find the smell of bark mulch to be very aromatic, and think of it as nature's perfume. I've talked to other guys who feel the same way.

No more. I recently had a truck load of bark mulch delivered. I checked its smell periodically, and instead of finding it pleasant, I found it repelling. So much so, that I actually tried to avoid getting my face near it.

When I ran out of this mulch, I picked up a few bags of hemlock mulch at our local Home Depot. The brand was Timberline, and was the dark variety. I thought hemlock would smell better. But it was worse. The smell in all cases was of strong moldy odor. None of the past bark aroma was there at all.

My mulch needs were greater than I thought, so I want back for more. Home Depot was out of the blue Timberline hemlock mulch bags, so I bought their bags of hemlock mulch that had red coloring on the outside. The mulch inside was of a red color. The mold smell was still there, but not as strong, and there was only a faint appealing bark aroma. I tried calling the Timberline manufacturer, but no one answered their 800 number. So I called their local number. No one answered, so I tried to leave a message, but their answering machine cut me off saying it heard no audio! So I tried to contact them via the Internet. Fortunately, I received a nice reply from their agent Kathy Perron, who said the hemlock came from "hemlock bark and composted forest products" in Maine (the next state over). The red mulch isn't really bark mulch (the bag calls it "Hemlock Mulch"), and is made from "softwood logs, ground and dyed with a carbon based dye". In summary, it cost more, had a slightly better texture, and less of a mold odor.

Unfortunately, my wife absolutely hated the redish color of the mulch (I liked it, thinking it was more of a red-tinted brown then red), so I went back again to Home Depot and this time bought Scott's mulch, made from forest products. This mulch also had a somewhat moldy smell with almost no pleasant aroma. It was also dyed - a nice "deep-forest" brown.


Consequently, after all this experience, now when my nose gets near this (bark) mulch, I hold my breath so as to avoid smelling it. What a shame.

So, why the change in bark aroma? I'm guessing it's due to white canker. Here's why. While white canker does infect leaves, microscopic examinations show it is primarily a bark disease. More specifically, white canker fungus feeds on the nutrient-rich inner bark, destroying it. While destroying it, the fungus prevents nutrients from migrating outward toward the outer bark. You can see this on the bark surface of infected trees - new bark often doesn't get created, and existing bark is cut off from the chemicals (often aromatic) that prevent other fungus from attacking and consuming it. In fact, bark on infected trees will simply look unhealthy, as if it is decaying. It is.

When such an infected tree is cut for lumber, the unhealthy, decaying bark is stripped off and ground up to produce bark mulch. This bark mulch therefore strongly smells of mold/fungus precisely because it contains a large amount of it.

A closely related issue is whether this infected bark mulch will damage the plantings it resides among. I don't think it's harmful, and so far I haven't seen any harmful effects. After all, all bark mulch will eventually decay naturally anyway. This natural decay is now simply given a head start, so the bark mulch probably won't last as long as expected. In fact, I'm seeing this now - the bark mulch I put down several weeks ago seems to be disappearing!

As do many others, I love the look of bark mulch. But based upon my experience with it combined with my research into white canker, I'd recommend avoiding "bark" mulch, and instead go with mulch composed of ground up wood, since the interior of a tree is usually not much affected by white canker.

Damn, I miss that sweet bark aroma!

[cmiller]

I wouldn't put much stock in the labeling. I used to have a favorite potting soil and told my friends, but this year the contents of the same packaging looks like chopped bark. It could be that "forest products" covers a multitude of sins, just as "animal by-products" in pet food covers some egregious ingredients.
In the alternative, it might be that you're getting a different type of bark.

I don't know your species there, but in MT we have "piss fir" aka white fir or grand fir, two Abies that smell like cat urine when cut. I've also smelled oaks that were just naturally awful-smelling. The devil's advocate position is that the manufacturer got a deal on some nasty bark from these species. Unless the bark is sterilized, i'd bet their are dozens of species of itty-bitties inhabiting the bark. Did you look at it under your microscope?


 

[cmiller]

Hi, Don. I wanted to report that when i was at Home Depot last Friday, i saw a bag of the Scott's mulch, dyed brown, was split, so i took a good whiff. It smelled pleasant, so either this batch came from a different source, or it was processed/stored differently. I wonder if it can mold in the bag...?

[Don Peters]

During the past week, I've been walking around my property, checking out the plants and trees. While doing this, I noticed that the bark mulch didn't look like it should look. So I examined it more closely. Then I checked out all the areas I had put down bark mulch. To my great surrpise, all the bark mulch had disappeared, and all that remained was a thin coating of wood chips! I'd never seen this happen before. Normally I find that bark mulch will disappear, or rot, after a year or so. Now, its life seems to be two months!

Noticing this, at first I was almost in disbelief. Then, as I thought about it, it seemed to make sense. White canker infiltrates the inner bark of a tree, soaking up the nutrients that should instead go into nourishing and creating the outer bark. That nourishment includes the infusion of anti-decay chemicals into the outer bark. If you carefully examine trees infected with white canker, you will see that the bark often looks unhealthy, as if it is in a state of partial decay. This unprotected bark is what goes into bark mulch. Soil bacteria (and white canker fungus), then, has a much easier time of digesting this bark mulch, and it takes advantage of it, especially when moisture is present. The other component of typical mulch, wood chips, isn't attacked much by white canker, so it remains on the ground after the bark disappears.

I've always liked the look of bark mulch, along with its moisture retention. But it looks like I'm going to have to find a substitute. I've tried grass, cocoa shells and wood chips, but I'm not fond of any of the bunch. So I'm still looking.

[CamKrist]

Similar subject was being discussed at yahoo answers last week. I can post the link if needed.

[Don Peters]

Yes, please do!