Size matters.

Yesterday I received a call from an administrator at a large military base.  (I have to tell you that anytime I get a call from someone in government I immediately start wondering about “the file” that I’m sure is kept on me.  No, I’m not paranoid, but I’m an outside reviewer for a number of graduate student theses from the University of Agriculture in Faisalabad, Pakistan.  In fact, I’m doing two right now.  So every once in a while I am sent a brown paper package from Pakistan.  They’ve always been opened and resealed by the time I get them.  But I digress.)   Anyway, the administrator from the LMB was concerned about a newly installed landscape on the base.  Requirements for landscapes around military buildings specify that plants must be placed a certain distance from the building itself, and not be tall enough to hide people or large objects.  So my caller was concerned that the winter creeper (Euonymous fortunei) which had been planted would start to do exactly what its name implies.  Furthermore, he had done a little Googling and found reports that this plant can get quite a bit taller than what the LMB specifications require.  However, the landscaper was adamant that this plant would not exceed the height requirements and cited one of Dr. Michael Dirr’s books as evidence.  So what, the caller asked, did I think about this?

Several years ago I wrote a myth column on plant size, which you can read here.  Part of this column immediately sprung to mind:  “The lack of consensus among tree identification guides, taxonomic literature, nursery tags, and real-life landscape specimens underscores the fallacy of assuming a uniform maximum height for any species, variety, or cultivar of any tree or shrub.”  In fact, the best predictor for mature plant size – especially for nonnative species – is performance in your local geographic region.  With this in mind, I called my colleague Dr. Sarah Reichard (an excellent plant taxonomist) at the University of Washington.  She laughed when I explained the situation and said that a local specimen at the Washington Park Arboretum had become such a nuisance that the grounds crew had to whack it into submission.  Not only was it well over 12” tall, but it had crept into the nearby Magnolia and was busy making itself at home.

Don’t have a photo of the Magnolia-eating creeper, but I do have this nice truck-eating ivy.

What about the Dirr book?  It’s an excellent resource, but it doesn’t necessarily take into account how climatic differences can influence plant height.  In contrast, the Western Garden Book (by Sunset magazine), though not an academic resource, does look at local plant performance in its descriptions.  I was also annoyed to find that this introduced species is invading the eastern US and is considered a weed in some states. There are lots of good plant choices out there.  Let’s not aid and abet the invasives.

So my caller was armed with definitive evidence and the landscaper will probably have to absorb the replacement costs.  The lesson:  don’t rely on books alone.  Do some legwork in your area to find out what plants are up to – literally.

Sidewalk-eating Japanese maple – not an invasive, but easily outgrows its “expected” space

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Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and an Associate Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

2 thoughts on “Size matters.”

  1. Thank you for this post. While I was living and gardening in the Southeastern US I always used the "maximum size" as a "minimum full size" since plants ALWAYS outgrew their supposed maximum size. Now that I'm in New England I have to recalibrate my estimations. Will the maximum size be closer to what I experience? I'll have to wait and see, I haven't even lived here through one season yet!

  2. Thanks for joining us, Diana! We have a saying here in Washington: if you live on the west side of the Cascades, you multiply the "maximum height" by 2. If you live on the east side, you divide it by 2. I'll be curious to hear what happens in your first New England winter!

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