Will cocoa mulch kill my dog?

Recently I was asked to comment about a rash of e-mails floating around cyber-space concerning the toxicity to dogs of mulch made from crushed cocoa bean hulls.  Cocoa mulch is by-product of cocoa production.  The dark brown mulch is aesthetically and aromatically pleasing, giving the garden a rich, chocolately scent.  Since theobromine, a naturally occurring compound in chocolate is toxic to dogs, the internet is now filled with cyber-legends of dogs eating cocoa mulch and keeling over dead.

According to an article published in the Journal of the American Veterinary Medical Association (JAVM June 1, 2006 p. 1644), cocoa bean husks can contain up to 2.98% theobromine.  The JAVN article state “no reports of lethal toxicosis from ingesting this mulch have been filed with the ASPCA Poison Control Center this year (2006). In 2004 and 2005, 16 reports of single exposure to the mulch were received, none resulting in death.”

The ASPCA posts this comment regarding cocoa mulch on its website:
“Dogs consuming enough cocoa bean shell mulch could potentially develop signs similar to that of chocolate poisoning, including vomiting and diarrhea. In cases where very large amounts of mulch have been consumed, muscle tremors and other more serious neurological signs could occur. To date, the ASPCA Animal Poison Control Center has not received any cases involving animal deaths due to cocoa mulch ingestion. One key point to remember is that some dogs, particularly those with indiscriminate eating habits, can be attracted to any organic matter. Therefore, if you have a dog with such eating habits, it is important you do not leave him unsupervised or allow him into areas where such materials are being used.”

It should be noted that processed cocoa mulch may contain much lower concentrations and some manufacturers market cocoa mulch that is ‘Pet safe’.  Consumers should look for products that are tested and certified theobromine free.

As always, I stand by my recommendation to use locally processed wood products such as ground hardwood bark and ground pine bark.  Plants grow well in these mulches, which are typically among the most cost-effective and natural looking (to me, at least) mulches available, and they are renewable and help support your local economy.

Should I boycott cypress mulch?

It’s hard to think of mulch as a controversial topic but, as with most things these days, we find people on both sides of an issue.  And, as with most things these days, some of opinions are based on substance, others are not.  In the southern U.S. some environmental groups are advocating a boycott of cypress mulch.

Cypress mulch is derived from baldcypress and pond cypress, which grow in ecologically sensitive wetlands in the Southeast.  Cypress wood is highly valued for is natural decay resistance.  Florida and Louisiana are the leading states for cypress harvesting for timber and other products.  In Louisiana it is unclear if cypress is logged solely for mulch but cypress harvesting for mulch does occur in Florida.  According to Dr. Jim Chambers, professor of Forestry at Louisiana State University and Chair of a governor’s science panel on forested wetlands in Louisiana, cypress mulch production is a sensitive issue.  “Many of our cypress-tupelo forests are in a severe state of decline. As you can imagine, these forests are very important to south Louisiana for many reasons. Areas permanently flooded, areas that are flooded for substantial parts of the growing season, and areas subjected to salt water input cannot regenerate. The amount of forested areas with these conditions continues to increase as subsidence increases, coastal wetlands are eroded by storms and human impacts on hydrology continue to degrade many sites.”

The inability to regenerate new stands of cypress is an important concern and calls into question the sustainability of cypress harvesting on these sites.  Chambers is working with environmental groups and others to develop a process to certify that mulch is produced from sustainable forest harvest operations

Another issue related to cypress mulch is a claim that is circulating in parts of Michigan (and perhaps elsewhere) that cypress mulch is linked to cancer.  I conducted a search of the National Library of Medicine and National Institutes of Health literature database (www.pubmed.gov) on ‘cypress’ and ‘cancer’.  The only hits I found were related to studies looking at falsecypress (Chamacyparis) extracts for anti-cancer properties, similar to taxol.  The claims of cypress mulch and cancer may be an amalgam of the environmental concerns over cypress harvesting discussed above and concerns over use of mulch derived from CCA (chromated copper arsenate) treated wood, which is used for decking and other uses similar to cypress.  Research has shown that leachate from mulch containing CCA treated wood can have elevated levels of arsenic and metals above established health standards.

We all know Linda’s fondness for wood chips as mulch.  My personal favorite is ground red pine bark for its durability and natural appearance.  The key is to look for renewable mulch products that are locally sourced.

Wonderful wood chips

I’m in love…with arborist wood chips.  These are not your beauty barks or other packaged mulches, but the chipped branches and leaves fresh from the tree crews. It’s a great way to keep this resource out of the landfill – and don’t even get me started about using this great mulch material for a “biofuel!”

I’ve written about wood chip mulches a lot, but thought today I would post some photos to show you how well they work in suppressing weeds and promoting growth in restoration sites.  We published a paper on this in 2005, though we’ve been using them in ornamental and restoration landscapes for about 10 years.

Here’s a recent project: a wetland buffer enhancement was being installed in an area that was covered in Scot’s broom (Cytisus scoparius) and blackberry (Rubus discolor):

Heron's Glen-6

We had a brush cutter mow it to the ground, then put a foot of wood chips down.  Later, we planted poplar, ash, willow and alder on the site:

We had to keep records, both written and photographic, for the county who monitors wetland projects.  So we took photos every year at the same points for comparative purposes.  Here’s what part of the site looked like immediately after planting and then after 5 years:

That’s not to say that we haven’t had to battle resurgent blackberries.  They migrate over from the wetland itself (which we can’t touch) and tip root.  But the increasing shade and competition from the trees has weakened their ability to take over, and the Scot’s broom has been gone for years.

So that’s one reason I love wood chips.  I’ll do a follow up some week showing how they can be used in the home landscape.

Rubber mulch rubs me the wrong way

I’ve been receiving a lot of questions about rubber mulch lately.  For those of you not familiar with the product, it consists of shredded tires that can be dyed and used on ornamental landscapes or under playground equipment.  In fact, the Obamas had this material installed underneath their children’s play structure at the White House.  It seems an ideal way to recycle the 290 million scrap tires we generate annually.

  

But is it?

It’s not effective:  One of the main reasons we use mulch is to suppress weeds.  Research has demonstrated that organic mulches such as wood chips, straw, and fiber mats control weeds better than rubber mulch.

It burns:  You’ve heard stories about piles of scrap tires catching fire and burning for weeks.  Well, those same flammable compounds are in rubber mulch, too.  When compared to other mulch types, rubber mulch is the most difficult to extinguish once ignited.  In fact, some parks and playgrounds no longer use rubber mulch or rubberized surfaces because vandals have figured out that rubber fires cause a LOT of damage.


It breaks down:  Although sales literature would have you believe otherwise, rubber is broken down by microbes like any other organic product.  Specialized bacterial and fungal species can use rubber as their sole food source.  In the degradation process, chemicals in the tires can leach into the surrounding soil or water.

It’s toxic:  Research has shown that rubber leachate from car tires can kill entire aquatic communities of algae, zooplankton, snails, and fish.  While part of this toxicity may be from the heavy metals (like chromium and zinc) found in tires, it’s also from the chemicals used in making tires.  These include 2-mercaptobenzothiazole and polyaromatic hydrocarbons, both known to be hazardous to human and environmental health. 

It’s not fun to be around:  When rubber mulch gets hot, it stinks.  And it can burn your feet.  Yuck.

The EPA’s website says this about scrap tires:  “Illegal tire dumping pollutes ravines, woods, deserts, and empty lots.  For these reasons, most states have passed scrap tire regulations requiring proper management.”   So if we have legal tire dumping (in the form of rubber mulch), does that mean it doesn’t pollute anymore?

(You can read a longer discussion on rubber mulches here.)

Mmmmm…mulch!

It’s a nice sunny September day in Seattle and I’m in my happy place.  What better topic to match my mood than mulch?

For those of you not familiar with my fixation on woody mulches, I’ll refer you to an article in MasterGardener Magazine here.  Briefly, I am a fan of coarse, chunky organic mulch, particularly arborist wood chips or other chipped material from trees and shrubs.

Rather than send this material off to the landfill, it’s so much better to use it as a protective layer on top of your landscape soil.  It’s a cheap, natural way to protect and nourish your plants, and provides a great habitat for beneficial insects and microorganisms.

Practically speaking, how does one move a mountain of mulch?  Shovels don’t work well, and compost forks have too much space between tines.  My favorite tool is the mulching fork.  It’s relatively lightweight, well balanced, and makes quick work of wood chips.

   

Sometimes you’ll find twigs in your mulch pile, or might have your own woody prunings that you’d like to use as mulch.  My second favorite tool is my electric chipper/shredder.  It’s powerful enough to deal with small branches and twigs and helps me create a more uniform mulch. Plus, I reuse my yard waste and keep the nutrients on site rather than throwing them away.

I don’t own stock in either of these products (my faculty salary doesn’t exactly allow me to be an investment tycoon). They’re just a few of my favorite things…

Mulch Volcanoes

After Linda’s post yesterday I just had to add my own 2 cents about gator bags.  I use ’em and I like ’em.  But, that said, I never allow gator bags to sit against trees for an extended period of time  (Maybe 6 weeks when the tree first goes in).  That’s just asking for trouble!  But looking at those bags got me thinking about a project which we’re finishing up this year.  Volcano mulching. Believe me, it sounds a lot cooler than it is.  Volcano mulching is when you make a big pile of mulch along a tree’s trunk, as in the picture below.

The reason we’re looking at volcano mulching is that everyone says it’s bad, but no-one has really proven that it’s bad.  The reasons that volcano mulching are supposed to be bad are twofold:  First, the mulch could cause rot on the tree’s stem (as with those gator bags) and second, because it might be possible for a tree’s roots to grow up into the mulch, potentially surrounding the stem, which might lead to the roots choking the stem as the tree grows larger.  Not a good situation.  Anyway, early in 2007 we took a field of maples and cut squares in their trunks, as seen below, and then either did or didn’t mound up mulch around these tree’s stems.

What we expected to see was that, over time, the wounding and presence of a mulch volcano would lead to diseases in the stem.  Instead what we found is that, for many of the trees, deeper mulch actually led to the wounds closing more rapidly.  The image below is of a wound that was covered with mulch.

While this next image is of a wound that wasn’t covered with mulch.

Of course some of the wounds without mulch closed fine as well, as you can see in the next image.  (Why isn’t anything ever cut and dried?)

So what does all this mean?  Well, nothing yet.  Research is a funny thing: it rarely gives you quick and easy answers.  I won’t recommend mulch volcanoes because we still haven’t examined those roots that may enter the mulch and surround the stem.  And before I say that the volcanoes didn’t affect stem rot in this study I want to take a closer look at those wounds by cross sectioning the tree which we’ll probably do this fall. Plus we’ve got to run statistics on all the different trees….. and then it would be great if someone else would take a stab at this study to confirm what we see…. I tell you what, nothing’s easy.