Nanomechanical oscillations…

This week one of our Facebook group members posted a link to a 2013 paper entitled “Love thy neighbour: facilitation through an alternative signalling modality in plants”. The premise in the paper is that plants are capable of acoustic communication and the experiment purported to demonstrate this. (I strongly encourage you to download the article from the link above so you can read it for yourself.)

chilisBriefly, chile seeds (Capsicum annuum) were placed into petri dishes, covered to ensure darkness, and then the dishes were placed in a circle. In the middle of the circle was either an empty acrylic box covered in black plastic (the control), an acrylic box covered in black plastic containing an adult basil plant (Ocimum basilicum) called the masked treatment, or an adult basil plant without a box (the open treatment). Seeds were watered and inspected daily for germination and the petri dishes were randomly rearranged.

According to the authors, “the presence of basil positively enhanced germination rates of chilli seeds, validating the claims of many gardeners who recognise the beneficial effect of basil on the growth of chilli plants.” Their reasoning is that the open and masked treatments induced more seed germination than the control. And since there was little difference between the masked and open treatments, they claim that the phenomenon is due to some signal other than light or gas (since the black plastic-covered acrylic container would prevent this).

How does this work? Well, according to the authors, this is evidence that acoustic signals are “generated in plants by biochemical processes within the cell, where nanomechanical oscillations of various components in the cytoskeleton can produce a spectrum of vibrations.” Never mind that the experimental design and methodology was laden with opportunities for experimental error. In particular, opening the petri dishes to water and count germinated seeds every day is deeply flawed. The easiest and least error-prone method would be to have the petri dishes sealed with parafilm to prevent water loss and inspected ONLY after the experiment was over. That is the standard method for testing for germination rates. Moreover, opening the dishes to count and water seeds every day really screws up the “covered to ensure darkness” part. In fact, chile seeds germinate better with light – which is what they got every day when they were opened. Was each dish exposed to light for exactly the same time every day? Exposure to light converts the seeds’ phytochrome to what’s called the active form, and phytochrome plays a crucial role in seed germination. The longer the light exposure, the more phytochrome is converted.

Now, plant scientists would know these things when they were designing their experiments. But as neither of the authors have degrees in plant sciences, it’s understandable. What’s not understandable is how this article got through peer-review. Unless none of the reviewers were plant scientists, either.

For those of you that belong to a university journal club or some other science discussion group, I think this would be a great article to discuss.

When trees can’t predict weird weather

Our normally mild corner of the country got hit early and hard with cold weather a few weeks ago. For several days straight, our home thermometer read anywhere from 22-25F. Now, Seattle routinely gets temperatures this low sometime during the winter. But this cold spell came very early – much earlier than our regionally adapted trees and shrubs were used to. The effect on our plants was significant.

20141112_080049Rhodies react to cold but tolerate the freezing temperatures

Trees and shrubs start getting ready for dormancy in the summer. They key in on the progressively shorter days and make biochemical preparations that are unnoticeable. When the first frosty evenings arrive, leaf color changes begin immediately. Chlorophyll, proteins and sugars are scavenged and stored in trunks and roots – we see leaves change from green to red, orange, yellow, and eventually brown. Slowly an abscission layer is laid down at the base of the leaf petiole, and when the layer is complete the leaf dies and falls.

But this year the trees weren’t ready. It got cold really fast, and green leaves died on the trees. And they are still there. Eventually these old leaves will fall, though some of them may stay on until spring.

Cold shocked leavesBoth the hydrangea in the foreground and the styrax in the back have retained their leaves after the cold snap.

What does this mean in terms of tree health? Well, it won’t kill them, but it does set them back in terms of food storage. A lot of the nutrients that were still in the leaves when they froze are lost to the tree. So there may not be as many reserves for winter root growth, or for spring leaf flush. Overall, we could expect to see less than normal growth in established trees and shrubs.

A scary Halloween story

Those of you that have followed the blog for a while know that poor tree planting is one of my pet peeves. It drives me crazy to watch tree installers use backhoes to gouge out gigantic holes and then drop in the intact root ball, clay, burlap, twine and all. But this dig-and-dump method (or “cost effective practice” according to installers) of installing trees often dooms them (the trees, not the installers) to a slow and ugly death. So in honor of Halloween, let me share my latest horror story.

Twice a day I drive down this street in NE Seattle. I’ve long admired the row of dead street trees left to remind us all of our own mortality. A few of these Liriodendron have somehow survived though “survival” seems a generous term. They’re more like zombies, slowly losing body parts but somehow still functioning until someone puts them out of their misery.

Dead #1 Dead #2 Dead #3

One lone tree seemed to defy all odds. Until our latest windstorm, which revealed the cause of all this arboricultural agony.

Downed tree Rootball side Rootball

That’s right, there’s the clay-covered rootball, still intact. Only one root has managed to escape into the native soil. There may be others on the opposite side, but by now (several years after installation) there should have been sufficient root establishment to prevent failure.

Several of us have written about bare-rooting trees before, and while there’s still not consensus on the practice I think we would all agree that the tree planting in this case was not acceptable. There are better ways, and yes they take more time (or “not cost effective” according to installers), but planting trees right mean fewer replacements later.

The great urban potato experiment

I don’t grow vegetables at home, mostly because I don’t have the space and partially because I don’t have the time. But I did want to try the potatoes-in-a-barrel method, which I also tried last year. But this year I planted about 6 weeks earlier (end of April) than I did the previous year (mid-June).  Here’s my mid-October harvests from both years:

October harvest  IMG_7560

Next year I’ll try planting even earlier. It’s not a huge harvest, but it’s fun to do, especially with kids. A richer media (like a green compost along with soil) might give you a better harvest.

If you want to try this yourself, here’s how to do it:

1) Use a plastic trash bin with holes drilled into the sides. Be sure to locate the barrel in full sun.

2) Put a layer of soil on the bottom, and add potatoes. (You can cut them into smaller portions, each with an eye, if you don’t have as many sprouted ones as I did.)

April planting 20143) Cover with soil and water well.

June 0554) As shoots and leaves emerge, continue to add soil or other media to the barrel, leaving the tops of the shoots and a few leaves exposed. I used a mixture of soil and composted wood chips. Water well.

June 0565) Continue to add media as needed, and continue to water through the season.

June 0106) When leaves begin to die back, you can dump the barrel onto a tarp and pick out your potatoes. Save the media for next year’s barrel.

Walnut warfare

Recently, a question about using black walnut chips for mulch was posted on our Garden Professors Facebook group page. As gardeners know, black walnut has a reputation as a chemical warfare species that will kill anything growing underneath it – a phenomenon called allelopathy. So it’s logical to wonder about the lethality of walnut chip mulches.

To get a good feel for the science behind black walnut’s allelopathic abilities, I was fortunate to find a relatively recent review on the topic (Willis, R.J. 2000. Juglans spp., juglone and allelopathy. Allelopathy Journal 7(1):1-55.). This well-written review includes a fascinating section on the historical background of walnut allelopathy, which was first mentioned in 36 BC by the Roman author Varro. But the science of allelopathy really started less than 100 years ago, when a Virginia researcher noticed the injury caused to tomato plants growing near black walnut (Juglans nigra) in his home garden. Subsequent experiments by him and others suggested that the orangish hydroquinone juglone leaching primarily from leaf litter and hulls.

SONY DSCSource: Wikipedia.

The research results on walnut, juglone, and allelopathy have been nothing if not inconsistent. For every report of toxicity in an exposed species, another report found no effect. In fact, much of the supposed allelopathy might instead be due to walnut’s highly competitive root systems, which could suck up available water and nutrients over a vast expanse of soil.

Black walnut tree Source: Flickr user davidburn

There are a number of other factors that help account for ambiguous results:

1) Juglone is not the only secondary metabolite produced by walnut species. They are loaded with a number of untested phenolics, flavonoids, alkaloids, terpenes and other quinones which could have allelopathic activity.
2) Juglone concentrations vary greatly among walnut species. They also have seasonal variability in the same individual.
3) Light conditions, rainfall, soil chemistry, and many other abiotic factors can influence juglone levels.
4) Organic matter and clay particles in soils can bind juglone, reducing its movement within the soil.
5) Microbial activity breaks down juglone.

Carefully controlled laboratory experiments can demonstrate juglone allelopathy to a number of plant species, especially at the seedling stage. However, there is little evidence from landscape level research to suggest that allelopathy is the reason that plants are damaged by being in proximity to walnut trees. In fact, the author of the review study concludes that even though Juglans species provides the best known and most widely accepted example of allelopathy, there is “still is no unambiguous demonstration of its effect” as “no one has as yet demonstrated that juglone is actually taken up by plant roots.”

walnut tree Source: Wikipedia

Where does this lead us in our discussion of walnut mulch toxicity? Fresh hulls and leaves appear to be the primary source of allelopathy, but not the wood. And even these sources may be quickly neutralized by soil conditions. Therefore, a walnut chip wood mulch should pose no danger at all to landscape plantings.

What’s wrong with this picture?

The  Seattle Times recently had a front page story on what Seattle’s new waterfront might look like. Back in 2009, the city began work on this project, hiring “rock-star landscape architect James Corner, designer of the celebrated High Line in New York City” to develop the big picture. (Note: I’ve been to the High Line and have posted on it before – it’s fantastic.) As you can see from the linked article from the Times, many of Corner’s architectural renditions for the greenway are presented, including this one:

An architectural rendering shows what a Pioneer Square beach at the foot of Washington Street could look like.

For those of you not familiar with Seattle’s waterfront, it’s built right next to Puget Sound, a huge inland sea connected at its mouth to the Pacific Ocean. So it was with much surprise that I saw what appear to be Douglas firs (Pseudotsuga menziesii) along the cobbled beach. Douglas firs are not particularly salt tolerant, nor would they be very happy with the tidal action or seasonal storms that will flood the beach on a regular basis. Even if these were not Douglas firs (native to Seattle) but some other salt-tolerant species (mangroves?), it’s doubtful they would look as picturesque as the drawing shows. Neither would the rest of the trees in the area, whose root zones would normally extend far into saline soils under the beach and sound.

Am I being picky? No, I don’t think so. Landscape architects should know better than to use plantings as decorations for their designs, like candy sprinkles on cupcakes. Plants aren’t just design elements. Choosing plants that are appropriate to a site is a science as well as an art.

I can’t believe that in the five years that Seattle’s been working on this project that horticultural science hasn’t been a major component of landscape planning.

Plant sentience – “It is happening…again”

Those of you who were Twin Peaks fans will recognize the title quote. And while my topic is not quite as scary as being stalked by Bob, the fact that plant sentience continues to rear its irritating head in legitimate scientific venues makes me want to curl up in a ball and whimper. Here’s what made me cringe: “Sound Garden: Can Plants Actually Talk and Hear?”

I posted on this topic a few years ago, and I’d invite you to read it and the accompanying comments. I’m still not a fan of anthropomorphizing plants, and I still think word choices matter, especially when you are trying to educate people about science.

It’s disappointing that some scientists are deliberately using anthropomorphic language when discussing plant physiology. The cynical side of me says it’s a great way to get press coverage.

April 2013 041 We’re watching you…

Bert, I’ll see your SOME-DED-TREES with POOR-DEAD-TREES

Bert’s done some nice posts on his SOcialME DesignED TREE transplant Study (or SOME DED TREES). I’m going to add to the discussion with a new addition to my Preventing Optimization Of Roots DecrEAseD TREE Survival (or POOR DEAD TREES) series.

It took a while, but the prediction I made in 2010 has come true. You’ll have to look at the link to see the whole story, but the bottom line is that this tree lasted only 7 years before succumbing to poor planting practices.

Here is the tree when it was planted in 2007. Note the lack of root flare (planted too deep) but the very obvious presence of orange nylon twine around the roots and the trunk.

Pine%202007.jpg   Orange%20twine.jpg

Here it is again in 2010. Note the dieback at the top and overall chlorosis.


And here it was yesterday.

Bush tree 2014Yes, it’s dead – dead and gone. I’m not sure exactly when it was removed, but it lasted less than 7 years. Conifers have lifespans of decades or centuries. There was no excuse for this poor installation, though I keep getting the argument from landscape installers that it costs too much to do it right (i.e., to remove the twine and burlap, if not the clay itself). Keep in mind that warranties only last for a year, so the property owner gets to eat the replacement cost caused by crappy installation practices.

We GP’s may continue to disagree about how much rootballs should be disturbed when planting, but I know that none of us would agree that planting B&B trees intact is a good idea.

New publication on biodynamics

Happy New Year to our blog readers!

Now that we have our blog safely moved to this new format, we all resolve to post more frequently. (It’s actually Bert’s day to post, but given that his computer is probably frozen – literally – in Michigan, I’ll step in.)

Today I got a link to my most recent publication in HortTechnology on the science behind biodynamic preparations. I’ve written about this topic before, but recognize the importance of peer-reviewed information for researchers, extension educators, and Master Gardener volunteers. Not to mention all the gardeners who rely on us to provide good science for gardens and landscapes. So here it is. I’m planning to continue submitting review articles to HortTechnology on other topics of interest. It looks like permaculture might be the next one up.

So enjoy this article – pass it on to others who are curious about biodynamics, and if you are a Master Gardener be sure to take it to your MG coordinator and ask that it becomes a resource for your program.


Whoo hoo!

I promise I’ll post something more substantial today…but I had to pass this email message along that I received this morning.  Way to go colleagues and commenters!

Hi Linda,

Your new weblog, the Garden Professors, is an impressive piece of work! I plugged it today in the consumer horticulture CoP blog [].


Bill Hoffman
National Program Leader (Ag Homeland Security)