Author: 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 a 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

Parking tickets, compost tea, and pseudoscience in the Ivory Tower

Back in November 2009, Jeff posted an educational and amusing commentary about Harvard’s use of compost tea. Much vigorous discussion followed, and we’ll return to that topic in a moment. But first, I’d like to tell you about my morning yesterday.

In September of 2010, I received a ticket for parking longer than 2 hours in a restricted zone. Now, there was no way I committed this infraction; I had hard core proof that could not be rationally challenged. So, armed with my husband’s affidavit as to my whereabouts, as well as a dated receipt showing I was at the post office at the time when I was apparently parked several miles away, I went to court to challenge the ticket. During our briefing, the sitting magistrate told us we would need to provide a “preponderance of the evidence” to win our respective cases. For me, it was an anticlimactic turn of events, as the citing officer (whom I’d subpoenaed) did not show up, so the ticket was dismissed for lack of evidence.

And thus we return to today’s subject – use of compost tea without a “preponderance of the evidence.” Jeff took Harvard to task for buying into this “bullpucky”, I think he called it, and now Berkeley has decided to drink the Kool-Aid. One of my dear colleagues at University of Washington forwarded me a link announcing that Berkeley Botanic Gardens was adopting compost tea as an “eco-friendly fertilizing method.”

As the article reports, compost tea is being used

1) as a disease suppressant
2) to provide nutrients, and
3) to reduce the amount of water needed.

I’ve written a lot about compost tea, and I’ve reviewed journal papers on the topic as well. In a scientific nutshell, there is no solid evidence to support use of compost tea, particularly aerated compost tea, in disease suppression. Likewise, there is no evidence to support a nutritional role (I just finished reviewing a manuscript on this topic and the data were unconvincing). Finally, I cannot understand why spraying compost tea onto the leaves of a plant would reduce its water requirements. The “preponderance of evidence” is truly lacking.

Students at Berkeley have the dubious honor of supporting this nonsense through their student fees: $11,000 has been spent on a 300 gallon tank, worm composting bins, and a spray tank.

Whatever happened to using good old compost, and letting nature create its own “tea?” (Compost used as a mulch also helps reduce irrigation needs.)

The roots of the rhody problem

There were several good shots at analyzing Friday’s unhappy rhododendron.  Mature leaf size can be determined by light levels, as both Lisa B and Tom &  Paul suggested.  Moving a plant from a low to high light environment could cause this change in leaf size.  This rhododendron hasn’t been recently transplanted, however, so we can eliminate light levels as a cause.  (And there was no other impediment to light, such as the presence of shading plants.)

Lack of nitrogen was mentioned as well; but a lack of nitrogen would have resulted in chlorosis in newer leaves as well as smaller leaf size.  In this case, the new leaves are not chlorotic.  (The chlorosis on the older leaves is probably a phosphate-induced iron or manganese deficiency.)

Foy alluded to issues with water…and indeed that’s what I believe is happening with this rhododendron.  Plants that exhibit smaller mature leaves in subsequent years are often limited by water.  Full turgor is needed to force leaves to expand fully; without this physical pressure from inside, leaves fail to expand and once cell walls have lignified, leaf expanion ceases. 

Lack of sufficient water during leaf expansion could be related to irrigation, though in our wet spring climate this is rarely a factor.  More likely is a problem with the roots themselves.  Definitive diagnosis would require digging up the plant to find out whether its roots are still encased in clay and burlap (my guess) or if something else is restricting their ability to grow beyond the planting hole. 

Friday puzzle: unhappy rhododendron

Today we have a diagnosis question. Consider this unhappy rhododendron:

While there is more than one problem with this poor thing, the one I’d like you to think about is why the newer leaves are smaller than the old leaves. (They are fully mature.) There are two parts to this question:

1) What is the physiological reason that the leaves are smaller? (In other words, what is directly causing this difference?)
2) Knowing this, what does this tell you about the underlying problem? (This is related to diagnosing what’s happening in the landscape that you could actually see if you knew where to look.)

I hope that’s not too confusing! I’ll monitor the blog over the weekend and add clarification if I need to.

Answer on Monday!

Random thoughts from the NW Flower and Garden Show

Last week was Seattle’s NW Flower and Garden Show. This multi-day extravaganza features display gardens, educational seminars, and many opportunities to spend $$$. I had a little free time one day and shot some pictures, which I present here along with my commentary:

The Good

The “perfect” lawn is no longer just a monoculture of grass.  At least two of the display gardens had flowers scattered for a designer version of ecoturf:

And a very cool repurposing of old heating vent covers as part of a patchwork of groundcovers:

The Questionable

A gorgeous Japanese maple (Acer palmatum), “born” in 1893:

I’m sorry. I have a real problem with digging up 108 year old trees for a garden display. I would be surprised if this tree will survive its relocation, wherever that might be.  (Perhaps there was an explanation for this that I didn’t see, but mature trees should be moved only if absolutely necessary.)

I also wonder about the ethics of digging up a 700 year old alpine spruce (Tsuga mertensiana). I’m a fan of salvaging plants on sites slated for development, but somehow I doubt the Canadian Cascades are being threatened with condos.

And things that make you go hmmmm…


Pot…socks?  Diapers?


Blackberry vines as tree decor

Mystery teeth revealed

Friday’s puzzle was tough!  Several of you were on the right track – this is a carnivorous plant. Right away Deb suggested a pitcher plant (then got sidetracked with chestnuts), but Derek was spot on with his guess of the “spiky bits” on a Nepenthes pitcher:

What the function of these spiky wings are is not clear to me; I did a little checking in the literature but failed to find anything convincing.  It does seem to suggest a close relationship with fly traps.  Perhaps the ancestral type was a fly trap type plant, which eventually evolved to an enclosed pitcher?  (Perhaps someone out there has a better grasp of carnivorous plant evolution than I do?)

And the scientific name?  Nepenthes alata, or “winged Nepenthes.”

Thanks for playing!

Friday mystery teeth

I’ve spent most of this afternoon at the NW Flower and Garden Show.  During my visit, I snapped a photo of this toothy plant part:

So the questions for today are….

What is this plant part?
What plant did it come from?
(And if you know its scientific name, that actually answers both questions at once.)

My husband is convinced this is too small a part of the plant for anyone to figure out the answesr.  I’m sure someone will prove him wrong!

Answer and a larger photo on Monday.

Tree terrors continue

You might remember back in October 2009 I gave one of the first Friday quizzes.  The featured tree had epicormic shoots, and Monday’s answer revealed the neglected wire staking that was slowly girdling the main trunk.  (Be sure you click on those links to see what the tree looked liked in 2009.)

I thought you might be interested to see what this tree looks like now:

A picture is worth a thousand words….many of those unprintable.

Update January 2022 – in response to a reader question, here is the tree in 2019 thanks to Google maps.

Tree teaser untwisted

Once again you had some great diagnoses!  The popular view was neglected staking material, and you were right:

Peter’s answer was my favorite (I love puns – the worse the better!).  Tom, I hestitate to ask about your previous experience here….

As usual, thanks to all of you for playing our quiz.  I’ll try to be better about doing this every Friday.  Our survey results indicated you like this feature a lot.