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

New study on pesticide use and GMOs

Some environmental extremists discount agricultural research done by universities, because they receive funding from Big Ag and therefore their researchers can’t be trusted. So this news report of a recent study by one of my Washington State University colleagues is doubly important: it dispells this baseless assertion and it provides some significant – and troubling – information about pesticide use and GMO crops.

Briefly, the article links an increased use of herbicides as a result of increased use of GMOs such as Roundup-ready crops. Weeds build up resistance to herbicides over time, meaning that Roundup becomes less useful as a weed killer and farmers have to turn to more toxic substitutes like 2,4-D to control weeds.

Dr. Benbrooks’s results, published in a peer-reviewed journal, are contested by the chemical industry, and other scientists question the seriousness of the problem. But next time you hear someone malign university scientists as being in Monsanto’s back pocket, please refer them to this post.

An unwanted bonus in your urban chickens

Longtime reader Ray Eckhart sent me a NYT story on urban chicken eggs and lead contamination.  As I’ve mentioned before on this blog, urban gardeners should have their soils tested for lead, arsenic, and other commonly found heavy metals before they plant edibles.  Chickens that are allowed to peck and scratch in metal-contaminated soils will pass that unwanted load on to you via their eggs.

So test your soils!  It costs a bit of money, but then you know exactly what’s lurking in there.  If your soils have significantly high levels of lead or other contaminants, you can still raise chickens as long as they don’t roam your garden.

Plant sentience – a slippery slope

I maintain a “Garden Professors blog” group on Facebook, where people can pose questions and make suggestions. Ellyn Shea asked about the trend towards calling plants sentient, especially given the new book by Daniel Chamovitz – What a Plant Knows: A Field Guide to the Senses

Dr. Chamovitz is a respected scientist, and there is no doubt that plants sense and respond to their environment in ways we are still learning to understand. But couching plant responses in language associated with human sentience is a slippery slope.  Yes, it makes plant physiology more understandable to nonscientists, but it also leads to increased belief in pseudoscientific ideas. For example, here’s a response to an on-air interview with the author (the link is my own insertion):

“Over a hundred years ago Rudolf Steiner wrote about biodynamics and plant growth. Their sensitivities to the seasons, their environments, and humans…”

Here’s another:

“I have been talking to plants for years…our experimental garden overflows, the cellular intelligence, the capacity to communicate is deeply satisfying when you learn how to listen and feel what the plant is saying…they give us much information at a spiritual level as well as physical, i thank my flowers verbally, i sing to them,they respond in healing ways…water has the same living intelligence…talk to a glass of water with love before you drink it and it actually improves the feelings of health and flavor ….”

And another:

“One who understands this far more thoroughly than Chamovitch is Stephen Harrod Buhner, author of The Lost Language of Plants and the Secret Teachings of Plants, in which he details the most cutting edge cardio-neurological science which demonstrates that the heart (more neurons than muscle cells) is the body’s primary resonator and capable of direct energetic communication with the rest of the living community. All indigenous and ancient peoples knew this.”

Plant physiology is drastically different from animal physiology, and what we’ve learned about how plants work comes from centuries of careful scientific study – not from folklore and superstition.  For those of us Garden Professor types who spend time educating the public about plant sciences, anthropomorphizing plants or using imprecise language just makes our jobs more difficult.

Why it’s important to prune tree roots before planting

This week I discovered that one of our center’s landscape trees is ready to bite the dust. I was sad – but also happy.  It’s a wonderful teaching moment and if the tree has to give up its life to save others, I guess that’s okay.

As the video will show you, this Japanese maple was planted some years ago with a root circling the trunk.  As both the trunk and root have developed in girth, we’ve reached a point where the trunk is constricted and the weight of the tree is splitting this V-shaped specimen down the middle just like a turkey wishbone.  We’ll just have to see how long it takes.

 

Bottom line: even though it takes a little more time to correct a flawed woody root system, it’s well worth the effort.

Point of view: tree fouls out

A few weeks ago the Seattle Times ran a story about a tree whose existence is straining a long-term neighborly relationship. The feud’s between former Mariners first baseman John Olerud and his neighbor Bruce Baker, both of whom live in the Clyde Hill area (a bit north of Bill Gates’ place in Medina). Baker owns a Chinese pine (red or white, I’m not sure, but I’m guessing red based on the photos) which interferes with Olerud’s view of Lake Washington and the Seattle skyline.

You can read the entire story on the link above, but I’m particularly interested in the following points from the article:

  • "The tree, with a 2-foot-thick trunk, was there long before the Oleruds built their home."
  • Baker "wasn’t willing to cut down a tree that his arborist called very rare and valued at $18,000."
  • Clyde Hill is "one of the first in the nation to adopt a process for condemning trees that block too much of neighbors’ sunlight or scenic views."
  • "You guys saw the trees," Olerud said at the board hearing. "They’re not attractive trees. I would say they’re the kind of tree that only an arborist would love."

So…what would YOU do if you were on the board making this decision? (Be sure to do your homework and read the entire article before weighing in.)

Deconstructing the cornmeal myth

Back in June of 2010, I wrote about an online column that recommended applying cornmeal as an antifungal soil amendment. (Important note: we are not talking about corn gluten meal. Just cornmeal.) The upshot of the post was while some gardening personalities extol the use of cornmeal to kill soil pathogens like Rhizoctonia and Sclerotinia, no published science supports the practice.  The post was effective in encouraging the author of the referenced online column to update her information, but the controversy didn’t die. In fact, new comments have been added to the original post on a fairly consistent basis, mostly in the form of personal anecdotes or angry rebuttals. Some commenters, however, have tried to carry on rational discussions, so today we’re going to look at cornmeal from a slightly different angle: what effect does it have on microbes in general?

To start, let’s look at the Stephensville, Texas research that’s most often highlighted by cornmeal proponents.  There’s no peer-reviewed work published on this specific research, but in an online copy of the Texas Peanut Production Guide I found a paragraph referring to “Biological Control of Soil-Borne Fungi.” Here it is in its entirety:

“Certain fungal species in the genus Trichoderma feed on mycelium and sclerotia of Sclerotinia minor, Sclerotium rolfsii and Rhizoctonia spp. All peanut fields in Texas tested to date have natural populations of Trichoderma. For several years, tests have been conducted in Texas using corn meal to stimulate Trichoderma development as a way to control the major soil-borne disease fungi. When yellow corn meal is applied to fields in the presence of moist surface soil, Trichoderma builds up very rapidly over 5 to 10 days. The resulting high Trichoderma population can destroy vast amounts of Sclerotinia, Sclerotium and Rhizoctonia. This enhanced, natural biological control process is almost identical to the processes that occur when crop rotation is practiced. The level of control with corn meal is influenced by organic matter source, soil moisture, temperature and pesticides used. Seasonal applications of certain fungicides may inhibit Trichoderma. Testing will continue to determine the rates and application methods that will give consistent, economical control.”

And that’s all there is on the topic. Most scientists would conclude that further testing was inconsistent and the researchers abandoned their efforts without publishing anything further. But this summary is at least a starting point, though it contains no data, references, or even authors.

First, there’s no argument that Trichoderma is a powerful antagonist of some nasty pathogenic fungi. Likewise, cornmeal most certainly can encourage the growth of Trichoderma, both in the lab and the field.  But cornmeal also encourages the growth of many other fungi – in fact cornmeal agar is commonly used for culturing fungi in the lab. So what about those three pathogenic fungi mentioned in the Texas peanut guide? Do they like cornmeal?

Indeed they do! Published research (about 20 or so articles) shows that cornmeal (not cornmeal agar) has been used to enhance growth of Rhizoctonia fragariae, R. repens and R. solani, Sclerotinia sclerotiorum and S. homoeocarpa, and Sclerotium rolfsii. In some cases the pathogens became more virulent in the presence of cornmeal.

Cornmeal is nothing more than a carbohydrate-rich resource that can be used by many microbes. If you happen to have a lot of beneficial fungi in your soil, cornmeal will feed them. If you happen to have pathogenic species in your soil, cornmeal will feed them too. So it depends on what fungi are already living in your lawn, vegetable garden, or rose bed on whether cornmeal will help, or just make disease problems worse.

The best thing to do – as the paragraph from the peanut guide suggests – is to mix things up a little in your landscape. Use mixtures of lawn grasses rather than growing a monocultural turf. Rotate plant placement in your vegetable garden every year. Add a microbe-rich organic mulch to your rose beds. Natural methods will keep pathogens in check much more effectively than a hyped-up home remedy that’s anything but antifungal.

UPDATE: Since this is a myth that refuses to die, I’ve published a peer-reviewed fact sheet on the topic. Feel free to pass on to others.

A plant riddle for you

This week Jeff, Bert and I are brainstorming new and exciting ways that The Garden Professors can invade…I mean integrate into…the gardening world. (We’re channeling Holly, who had a conflict with another even this week.)  We’ll leave discussion of the particulars for another day.  But that’s my segue into my text-short but picture-perfect invasive plant story.

Earlier this spring I was in Palm Desert and spotted a large clumb of purple fountain grass (Pennisetum setaceum) in a landscape:

So here is the riddle: Why did the fountain grass cross the road?

To get to the other side.

One solution to invasive species – assisted succession

For a couple of weeks now we’ve had some animated discussions on introduced plants (invasive or otherwise) and native species.  One of our commenters wondered whether many introduced invasives (those that take advantage of disturbed conditions) would eventually become controlled through succession (which in our part of the country means land dominated by trees and shrubs). And yes, if native species can get a foothold in an infested site, invasive species become less dominant.

To illustrate, I’ll take you on a virtual trip in our neighborhood’s pocket wetland.  In 2000, this tiny triangle was dominated by reed canary grass (RCG) and had been for years; a few blackberries, cattails and nightshade were the only other obvious species.


The triangle in 2000 looking west….


…and east

The city would mow the grass every so often, along with trees that my neighbors had futilely planted.  We decided to take this on as a class project (this was when I was on faculty at University of Washington).

When we began to clear out the vegetation, we were stunned to realize that there was a creek running through what seemed to be a flat chunk of land.

We cleared out as much RCG as possible and mulched the entire area (note that many restoration ecologists recommend taking out soil to a depth of 18″ to remove all the stolons).  We knew the grass would come back, but our task was to jump start the system and get some native plants started.  We installed a single Douglas fir and a single western hemlock (these are large trees at maturity), along with live stakes of native willow, dogwood and snowberry.  We planted a few Oregon grape and other smaller shrubs.


Live stakes planted through coir cloth (used to temporarily hold mulch in place).


The 2001 installation, looking east.  The Douglas fir is next to the group, and the hemlock is in the foreground.

Over the next few years the RCG came back with a vengeance.  We held occasional work parties to keep the grass at bay, but after I took a new position at WSU I no longer had the student work force that allowed me to keep this area partially controlled.  It became a one-family project, and not one that we had a lot of time for.


2003 work party dredging out the creek. You can’t see the natives we installed in 2001, but they’re in there.

Fortunately, nature took over for us.  The willows we had planted grew like weeds, creating a canopy under which RCG doesn’t do so well.

The Douglas fir and hemlock got established, as did the snowberry and one Oregon grape.  For the most part, we were able to weed whack the RCG on the very steep slopes and keep the flatter areas covered with wood chips.


Restoration site in 2009, looking west…


…and east.


Eight year old Douglas fir…


…western hemlock…


…and snowberry.

Will the RCG ever be completely gone?  I doubt it; the seedbank must be incredible, and there are many other RCG colonies upstream. But it no longer dominates the landscape: it’s become assimilated.  And that’s really the point: nature adapts.

[As an aside: I really don’t like the term “restoration.” We’re not taking landscapes back to some pristine original as the term implies.  “Assisted succession” more accurately and realistically describes this process.]

Our first GP Google hangout

We just finished our first hangout on Google+. Jeff moderated the discussion, which was both lively and productive. He recorded it too and posted it on YouTube. (I’m trying to embed it here as well – may take me a few tweaks so bear with me. Once it’s on, I’ll delete this parenthetical comment.)

Stay tuned for our next hangout and feel free to join us – we don’t bite!

The coolest plant from Costco

Since we have an almost 18-year-old with perpetual FDD (food deficit disorder), we do a lot of Costco shopping. I always take a walk down the bagged bulb aisle to see what interesting things I might try at home. This year I bought a bag of Tigridia grandiflora, aka peacock flower. Wow! What a lucky choice for me!

These iris family members have been flowering continuously since sometime in July. They do tend to be a bit floppy. I’ll probably add a plant support to keep it out of the pathway.

As far as I can tell from the sketchy information (for this species anyway), Tigridia species are native to central and south America. No record of any invasiveness, and for me it’s been completely pest free.

Anyone else enjoying these summer bloomers?