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.

Long term problems with Tree Gators?

So, Bert, you (and others) have done research on Tree Gator-type products and found them useful in providing water to newly planted trees and shrubs.  For those of you that haven’t seen supplemental irrigation products, they are heavy-duty plastic bags that zip up to create a sleeve around tree trunks and drip water from their perforated bottoms (Figure 1).  The City of Seattle uses them routinely, but I’ve seen a number of trees fail in spite of the additional irrigation.  While many of these failures are undoubtedly the result of poor root systems, inadequate root preparation, and/or improper installation (Figure 2), what worries me is the long-term effect of these sleeves on tree trunks.  I’ve seen nothing in the scientific or professional literature about this possible problem.  So I thought I’d do an informal assessment of Tree-Gatored trees.  Given what I’ve found, though, I’m tempted to do a more structured survey.

  
Figure 1.  Tree Gator                           Figure 2.  Poorly planted tree

First, I found a number of Tree Gators that were empty – probably close to half were nearly or completely drained.  These devices don’t too much good if they aren’t kept filled.  That’s an easy problem to fix compared to what I found when I unzipped the bags to look at the tree trunks.  When the bags are full, they press against the trunk, creating a humid, dark environment (Figure 3) that’s only made worse when rainwater seeps into the space.  As you can see in Figure 4, over time the bark rots, allowing insects and disease into the living tissues.  The insects ran when I opened the bags, but I saw numerous pillbugs and millipedes – which feed on decaying matter – in those trees with rotting trunks.

     
Figure 3.  Unzipped Tree Gator                      Figure 4.  Rotted bark
(note wet bark on lower trunk)                  (note millipede on left side)

I think there can be fatal problems for young trees when these bags are used long-term.  IMO, supplemental irrigators that resemble rubber donuts laid over the root zone are better designed.  I would be sure to have a mulch layer protecting the soil from compaction by these water-filled rings, but at least the trunks are left uncovered.

Introducing Bert Cregg


Welcome to the Garden Professors.  I am currently an Associate Professor and Extension Specialist in the Department of Horticulture and Department of Forestry at Michigan State University.  I am also about the last person I thought would be doing a blog.  I have often wondered who has time to read blogs, let alone write one.  But I was intrigued when Jeff Gillman invited me to participate in this one.  I have a lot of respect for Jeff and for Linda Chalker-Scott.  Both have contributed a lot to landscape horticulture by critically examining the various myths that pervade gardening.

My background:  I’m originally from the great Pacific Northwest; born and raised in Olympia, Washington.  I was fortunate to go to Olympia High School, which offered courses in Botany, Ecology, and Forestry.  Mr. Walt Chance, who taught Botany and Ecology, sparked my interest in plants and trees in particular. I got my B.S. in Forest Management from Washington State University and then did graduate work in tree physiology at Oklahoma State University (M.S. Forestry) and at the University of Georgia (Ph.D. Forest Resources).   I began working on tree nursery and urban forestry-related issues with the USDA Forest Service and continued to research tree nursery issues as a scientist with Union Camp/International Paper.  Since 1999 I have been on the faculty here are MSU developing research and extension programs that deal with landscape, nursery, and Christmas tree issues.  I am currently involved in production issues related to container-grown trees and issues related to the Emerald Ash Borer outbreak.  I also write and speak on landscape conifers.  If you are interested in some of my research and professional publications you can wander over to my faculty web-page http://www.hrt.msu.edu/faculty/cregg.htm   I live on a 5-acre farm in Dewitt, Michigan with my wife (Terri, whom I also met in Athens), our daughter (Hannah), two dogs, two horses, and an undetermined number of barn cats.

For my part, the theme of the blog follows Will Rogers’ famous line, “It’s not what we don’t know that causes us trouble, it’s what we know that ain’t so.”  As Jeff and Linda have documented in their books and articles, there is a lot of science related to landscape horticulture that we choose to ignore.  So, if you don’t like the facts getting in the way of a good story then this blog is probably not for you.

As we launch this blog, I’d like to add another quote from Will Rogers, the one he used to end every show.  He stated simply, “I never a met a man I didn’t like.”  The quote is remarkable because Rogers certainly met a lot of people that didn’t like him as he used his razor-sharp wit to carve up politicians and public figures of every stripe.  But Rogers’ too-short life proved that we can disagree without being disagreeable; something sorely lacking in all forms of discourse these days.  As we grope our way through the electronic age, many people hide behind the anonymity of the internet to spew all sorts of venom.   By intent, this blog will touch on some controversial issues and we don’t expect readers to agree with everything we write.  Our goal is to raise the level of dialogue about Horticulture; put some ‘meat’ and some science in the mix.  This blog has a ‘comment’ bar and we encourage you will use it, but ask that we keep the focus on content not character.

What I Learned This Summer (Part 1)

Just flew in from St. Louis and boy are my arms tired! [Baadum – ch!]

I have very diverse responsibilities and interests, but all in one way or another relate to this thing called Gardening. I recently attended two very different conferences, both in St. Louis but thankfully scheduled back-to-back. The first was the Perennial Plant
Association (PPA): a colorful, enthusiastic, slightly eccentric group of growers, breeders, designers, and geeks of the highest order. Bus tours and talks centered on plants, glorious plants….of which we simply cannot get enough.

  Paul Westervelt is so excited...PPA visits Missouri Botanical Garden

Hot plants!!! Paul Westervelt expresses his enthusiasm during the PPA tour of the fabulous Missouri Botanic Garden.

The second was the American Society for Horticultural Science (ASHS) annual conference. Not so colorful. Lots of data…even presented some myself. But very necessary – especially in our realm (publish or perish). “Horticulture” is a ridiculously broad umbrella, under which falls food crops, ornamentals, biotechnology, econom cs, and some social sciences.  There were speakers and posters on a mind-boggling array of topics – from horticulture curricula to stress physiology; tropical fruits to public horticulture. Some of this research and information is ready for “technology transfer”, that is, with a bit of tweaking,
the results are directly applicable, whether to a nursery grower or a consumer.  Much of it is not; and will exist only in that “researcher to researcher” ether.

My point: there are many outlets for the information shared at PPA, i.e. hot new plants on the Terra Nova website, design articles by the various garden writers in attendance, the newest book from Timber Press, etc. For ASHS, not so much, unless you subscribe to HortScience and receive the 1000+ pages of abstracts from the meeting.

This is where we can help. Jeff Gillman has done a yeoman’s job at translating science to gardeners, and now all of us involved in this blog are going to chip in.  Call it “insider
information” or the less-glamorous “stuff that’s technical/boring to read but with
hidden nuggets of usefulness”.  The one thing we hope makes this useful to you is that we all consider ourselves gardeners, and though our day jobs certainly inform how we manage our own little piece of heaven, you’ll get a good dose of adventure, frustration, triumph, plant lust, and humor.

My next few blog contributions will be “things I learned in St. Louis”.  Not least of which is the hoppy goodness of locally-brewed Schlafly Pale Ale.