City Mulch - Is It Good for the Garden?

City Mulch - Is It Good for the Garden?

Part of Ep. 1903 Plants For Clay & A Garden That Rocks

Most gardeners think free is good, but what about free mulch from the city? Plant Pathologist Brian Hudelson warns that using free mulch without knowing what's in it could add diseases to a garden.

Premiere date: May 11, 2011

TRANSCRIPT+
Wisc Gardener Transcript: 

Shelley Ryan
I’m with UW Extension Plant Pathologist Brian Hudelson.  You know, Brian, as gardeners I don’t know, I ‘m always on the lookout for freebies.  Free plants, free mulch, you know, anything I can get free. 

Brian Hudelson:
I’m definitely looking for free stuff too, but sometime it’s not the best of ideas. 

Shelley Ryan:
Free plants are. 

Brian Hudelson:
Free plants can be certainly.  But where I would be a little bit leary is about free mulch. 

Shelley Ryan:
And why? 

Brian Hudelson:
Well, a lot of the mulches that are free tend to be materials like this that we have here that have been chipped up by a city municipality. 

Shelley Ryan:
Right, the stuff, yeah. 

Brian Hudelson:
Just think about what might be going into that material.  It’s usually trees that have been probably sick or dying.  There is a problem of potentially bringing in disease causing organisms in this particular mulch. 

Shelley Ryan:
So this is the stuff that’s usually in a pile.  Even our village has something like this. 

Brian Hudelson:
Local park, something like that where you can come and take a bucket load, or however much you want, and take it back to your home. 

Shelley Ryan:
Yeah and it’s free. 

Brian Hudelson:
Yeah, it is free.  But it may not be so free, because you may end up killing off a lot of your plants. 

Shelley Ryan:
So disease causing organisms that are serious, specifically? 

Brian Hudelson:
The one that I’m concerned about is one called verticillium, which is a soil born pathogen.  It’s got a wide host range.  It will take out trees like maples and ash, some of our very common street trees, and also things like redbud, magnolia, liriodendron, smokebush, and also herbacious plants as well. 

Shelley Ryan:
Well, and I’m holding these for a reason. 

Brian Hudelson:
Definitely, vegetable crops are also susceptible, things like eggplant particularly susceptible to verticillium, and potatoes and tomatoes as well. 

Shelley Ryan:
Susceptible doesn’t mean they’re going to just suffer, they’re going to die. 

Brian Hudelson:
This tends to be a fatal disease. 

Shelley Ryan:
They’re going to die. 

Brian Hudelson:
We do have some good information based on some work by a graduate student that worked with me, that this type of material can harbor verticillium.  She actually chipped up trees where she knew they had verticillium, and then monitored those chips over time and found that she could recover verticillium for at least a year after she chipped up the trees.  She was also able to use the chips to actually infect plants, including eggplant. 

Shelley Ryan:
So the pile I have in my front yard tha’t been there for a year is still not safe. 

Brian Hudelson:
We don’t know about that.  We know that in can survive for quite a while.  The other issue is a lot of broadleaf plants, particularly weeds, can be susecptible so they can become infected and actually harbor the fungus. 

Shelley Ryan:
The weeds become a carrier. 

Brian Hudelson:
Basically yes. 

Shelley Ryan:
Oh, wow.  Well, the other problem I worry about, especially in my neighborhood, does this little pile of chips contain walnut. 

Brian Hudelson:
Definitely a possible issue, because walnuts produce toxins, those are water diffusable toxins.  That will be in the chip material, and they can stop a lot of different plants from growing. 

Shelley Ryan:
Right, I mean they’re not dead, they just don’t grow. 

Brian Hudelson:
They just don’t grow.  It can kill off some types of plants as well. 

Shelley Ryan:
Yes. 

Brian Hudelson:
So you have to be careful with walnuts as well. 

Shelley Ryan:
Okay, so no more freebies of that.  But there are actually there are some mulches that we pay a fair amount of money for that are dangerous, too. 

Brian Hudelson:
Possibly yes.  The one that I think comes to mind most commonly is cocoa bean mulch, which is just wonderful stuff in terms of the smell.  It smells like cocoa.  Unfortunately, this can be toxic to dogs. 

Shelley Ryan:
My dog loves chocolate. 

Brian Hudelson:
A lot of dogs do. 

Shelley Ryan:
Yeah and it’s very dangerous. 

Brian Hudelson:
It’s very dangerous for them. 

Shelley Ryan:
Very dangerous to them. 

Brian Hudelson:
It can be deadly, quite frankly.  The other thing I worry about this particular mulch.  You apply it, and I don’t think it lasts particularly long.  I usually see it starting to mold and mildew after probably about 2-3 weeks. 

Shelley Ryan:
Really?  That’s a very short time. 

Brian Hudelson:
A very short period of time, particularly if we have wet weather.  The other thing I’m concerned about with cocoa bean mulch is there’s a particular pathogen it’s called the Southern Blight fungus, that we are concerned may come in in cocoa bean mulch. 

Shelley Ryan:
Really? 

Brian Hudelson:
It’s a southern pathogen, this is a southern crop.  We do think occasionally a batch of this sort of mulch can be contaminated.  We don’t have any formal research on that, but just some observations that I’ve made from samples coming into my clinic.  That’s a devastating disease.  It will actually kill off pretty much anything that is herbacious.  We had an infestation of this fungus at the Allen Centennial Gardens at the UW-Madison.  By the time I was called out, there was about a 40 square foot area that had been where all the plants had been killed off. 

Shelley Ryan:
Wow, that’s a lot of plants in 40 square foot. 

Brian Hudelson:
Huge area, yes. 

Shelley Ryan:
That’s a lot. 

Brian Hudelson:
A lot of material. 

Shelley Ryan:
So, dangerous to pets, dangerous to our plants maybe even too. 
Brian Hudelson:
Potentially. 

Shelley Ryan:
Potentially, okay.  How about the pretty bucket you’ve got right there? 

Brian Hudelson:
Yeah, this is one of the dyed mulches that you can commonly buy at most big box stores or garden centers, or wherever you buy your gardening material. 

Shelley Ryan:
It comes in many different colors.  This one’s really nice. 

Brian Hudelson:
Yes, indeed, kind of a red color.  I don’t have any formal reason to dislike this based on research, but my concern is always you don’t know exactly what it’s been dyed with.  So I would be a little bit caucious about using this around vegetable crops or somethings that’s edible.  I do have to admit that the bag of this that I bought had a warning on it that it wasn’t to be used in a playground area, so that shoots up some red flags as well for me. 

Shelley Ryan:
Makes you wonder.  I’d be hesitant maybe around kids, pets and vegetables. 

Brian Hudelson:
Definitely.  Also, you know, use it around your ornamentals. 

Shelley Ryan:
Okay, it’s kind of like the city mulch, when we don’t know what’s in it, be cautious. 

Brian Hudelson:
Be cautious about it. 

Shelley Ryan:
Okay, then what do you recommend, Brian? 

Brian Hudelson:
What I love is red cedar mulch, which I think smells good. 

Shelley Ryan:
It’s pretty. 

Brian Hudelson:
I think it lasts quite a while.  I usually don’t apply this more than about every couple of years or so in my garden. 

Shelley Ryan:
Oh, that’s good to know. 

Brian Hudelson:
The other thing I don’t worry about too much with this is disease organisms. 

Shelley Ryan:
It’s not going to bring something in. 

Brian Hudelson:
Probably not, no. 

Shelley Ryan:
Okay, and what about oak? 

Brian Hudelson:
I really like shredded oak bark, as well, as a mulch.  I think that’s a good material as well. 

Shelley Ryan:
I see bags of it but I hesitate to buy it, because of the oak wilt. 

Brian Hudelson:
I’m not concerned about oak wilt in that particular material, because of the way that organism is moved around.  It’s either by typically by sap beetles or through root grafts, and I wouldn’t think that the sap beetles would be really interested in visiting your mulch. 

Shelley Ryan:
But this is still your number one favorite. 

Brian Hudelson:
This in my number one just because of the smell. 

Shelley Ryan:
Do we have to worry about this pulling the nitrogen out? 

Brian Hudelson:
If you’ve got good material that’s been aged well, I would not worry about that, no. 

Shelley Ryan:
Okay, so it’s fresh green manures, grass clippings. 

Brian Hudelson:
Grass clippings, that sort of thing that I would really worry about. 

Shelley Ryan:
I see a lot of places where they’re using rock or gravel as mulch. 

Brian Hudelson:
Also not my favorite either, because I think what that does is it tends to absorb a lot of heat from the sun.  That will heat the root system of the plants underneath and that can be very stressful and lead to other problems. 

Shelley Ryan:
Well, it’s also heavy, it compacts the soil. 

Brian Hudelson:
So it’s not good for us putting it in either. 

Shelley Ryan:
Yeah, it’s heavy for us, too. 

Brian Hudelson:
That’s right. 

Shelley Ryan:
So stick to the red cedar. 

Brian Hudelson:
That would be my suggestion. 

Shelley Ryan:
Okay, thanks, Brian. 

Brian Hudelson:
You’re welcome. 

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