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 Linda Chalker-Scott

I’m an associate professor in the department of Horticulture and Landscape Architecture at Washington State University.  I’m also an Extension Specialist in Urban Horticulture, meaning that I have a global classroom rather than one physically located on a college campus.  I’m trained as a woody plant physiologist and I apply this knowledge to understanding how trees and shrubs function in urban environments.  This is a fancy way of saying I enjoy diagnosing landscape failures – sort of a Horticultural CSI thing.

I’m a native Washingtonian, but I spent my academic life at Oregon State University and then moved to Buffalo for my first university position.  I moved back to Seattle in 1997 and worked at University of Washington’s Center for Urban Horticulture.  In 2001 we were fire-bombed by ecoterrorists (and yes, the irony of the greenest center on campus being targeted by ecoterrorists is not lost on me) and I lost my ability to do lab work.  During this time I developed a more applied research program and in 2004 I began my Extension position with WSU.

Jeff and I have never actually met, but we’ve been chatting via internet for some time.  Apparently he manages his time better than I, since he has the ability to spearhead this blog on top of everything else he does.  I know I’m looking forward to this new venue for discussing the science behind America’s favorite outdoor activity (assuming that’s still gardening and not Ultimate Frisbee or frog licking).