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

Friday puzzle answer

So many interesting answers to Friday’s puzzle – thanks to all of you for putting out the effort!  It most certainly is an abiotic problem – but was it temperature, suggested by Deb?  Water, suggested by Foy, Gayle and Ed?  Light, suggested by Nancy?  My plan was to have an extensive soil test run to address the possibility of pollution (suggested by Jim, Heather and Paul), except we discovered the source of the problem last summer when we finished digging our pond:

 

As you can see in this photo, we have solid clay about 12″ below the surface.  (And I do mean solid.  I’ve kept lumps of the stuff to take to seminars, so when people say “I have clay soil” I pull this out and ask if this is what they mean.  Usually not.)


So in this area of our yard we have a perched water table: the water percolates through the topsoil, hits the clay, and spreads horizontally.  When we had turf in place, it tended to keep the upper few inches relatively dry, which allowed the dogwood roots to survive.  When we took out the turf and covered it with wood chips (to conserve water!), the soil became saturated nearly year round.  We dug out the tree a few weeks ago, and this is all that remains of the root system; the rest of the major roots had rotted away:


We’ve replanted the tree in another area of the yard with much better drainage, and we’ll keep track of its establishment and leaf size.  I think it will recover, as new roots will emerge from the main root mass.

(Paul, thanks for the kudos on the fence design!  My husband built this, and he’ll be pleased to see your comment.)

Friday quiz time!

Now I could have sworn I’d posted this puzzle before, but after searching through all the previous postings I can’t find it.  Here it is.

I planted this Cornus kousa in 1999 (removing the burlap, clay, etc. prior to installing).  We removed the turf (still attached to the $(%&$ plastic mesh) and planted the tree in the existing soil.  The first photo was taken in 2004, and the second was taken in 2007:

 

Here are some specifics about what was done to the landscape during this period: we replaced all the turf with wood chips and put in the fence as shown.  There was no impact on structural roots from either of these activities, and fine roots were affected minimally when we dug post holes for the fence.  The turf was simply allowed to die back in the summer (hot summers do that here in Seattle) and then topdressed with wood chips.  There were no chemicals applied, nor was there any soil disturbance.

It was about 2007 that we noticed the leaves were substantially smaller than previous years.  The leaves are sparse and small, but they don’t become chlorotic or necrotic during the summer, nor does any part of the tree suffer more than any other.  This phenomenon has continued until this year, when we finally dug it up and moved it elsewhere.

So here’s the question:  why did this tree start swirling down the mortality spiral?  As always, there may be many legitimate answers – but I’ll show you the actual reason on Monday!

Enjoy your weekend!

Protecting existing trees – what a concept!

I just got back from a trip to Pullman where I guest lecture once a year for the Landscape Plant Management class.  It’s also a chance to get some new photos for my Wall-O-Shame.  Here’s my latest:

Pin oak (Quercus palustris) doesn’t drop its leaves in the winter – instead, they hang on until the following spring.  So it’s really easy to see which part of this tree is alive (i.e., has last year’s leaves).  It’s apparent that most of the crown has died, with only some lower scaffold branches remaining.

How did this happen?  Take a look at how new that concrete is around the base of the tree (and how small the tree well is.  This construction was done in 2004:

Note the complete lack of root zone protection.  Not only has the majority of the tree’s fine roots been destroyed in preparation for pouring concrete, but only a very small space under the tree is “protected.”  I guess the cup at the base represents the irrigation system.  To top it off, this construction was done in August, when coincidentally I was there as well.  It was blistering (as it usually is in the summer in eastern Washington), and the remaining leaves on this tree were wilted:

So why would anyone be surprised when, 6 years later, this tree looks like crap?  And why doesn’t WSU insist on tree protection standards when construction bids are submitted?

Friday mystery revealed!

Good sleuthing over the weekend!  As John, Karen, Jimbo and Al suggested, there is something stuck on the side of this Norway maple (Acer platanoides, which is Latin for “maple that takes over the planet”).  In fact, the reason that I, with my pathetic ID skills, know that it’s a Norway maple is because it’s a nursery tag stuck in the tree:

This type of injury really bugs me, because it’s entirely preventable.  One of the cardinal rules of transplanting trees and shrubs is to remove all foreign material.  And this is a perfect example of why.  I don’t know the history of this tree, but this is was I think happened.

The tag was on a branch of the young tree; as the branch increased in girth, it became girdled by the plastic and died back.  At the same time, the girth of the tree increased to encompass the base of the branch and the tag.  The dying branch was either torn from or broke off the trunk, creating a tear in the bark and creating the horizontal scarring at the base of the wound.

If you’re hopeless with plant names (like I am), keep an electronic database of all the plants you’ve installed in your landscape, including the name, the date installed, and any notes, especially for failures (e.g. not cold hardy enough, invasive, too large, slug snack, etc.).

Friday mystery photo

Today’s photo is courtesy of Photoshop technology.  I’ve edited the damaged area so you can’t see what caused, or at least contributed to, the damage:

Now before you complain that I’m cheating (which I am!) keep in mind that what I edited out could have been removed before you were asked to diagnose this injury.  I will tell you that it’s not due to pests or disease.  As is so often true in real life, there could easily be multiple correct answers.  On Monday I’ll provide an untouched photograph and rail against the all-too-common practice that can cause the damage.

Have a great weekend!

You say tomato, I say phytochrome

Yesterday I got an interesting email about a new product – a Tomato Automator.  Briefly, this square, red plastic disk slips around the stem of a tomato plant to suppress weeds and pests.  Most intriguingly, we’re told that the color “triggers a natural plant protein that makes tomatoes mature faster and product more fruit.”

Given this is a red product, it’s likely that the protein referred to is phytochrome (literally, “plant pigment”).  Phytochrome activity is maddeningly complicated to explain, so we’re going to keep this simple and refer (somewhat inaccurately) to “active” and “inactive” forms of phytochrome.  The active form of phytochrome exists when red light is predominant and encourages leaf expansion, chlorophyll development, and other characteristic of plants growing in full sun.  In contrast, the inactive form of phytochrome occurs when red light is reduced, either at night (when there’s no light) or in shaded conditions, where far-red light is predominant.  (Far-red light occurs just outside our range of visual perception but is absorbed by phytochrome.)

From a practical standpoint, this means a plant can “tell” whether or not its light environment is limited: both red and blue light are absorbed by chlorophyll, so a low level of red light means poor photosynthetic conditions.  Under such conditions, “inactive” phytochrome causes many plants to become etiolated (have abnormally long stems) in an attempt to outgrow the shade before it starves from lack of carbohydrate production.  In addition, this photosynthetically-poor light environment can also increase fruit set by redirecting resources to seed production rather than foliage  – perhaps a plant’s last effort to reproduce before it dies.

OK, now onto the useful application of this information.  Several years ago researchers investigated that effect of different colored plastic mulches on tomato production.  Again, to keep this simple we’ll just focus on the effect of red mulches.  It’s pretty much agreed that red plastic mulch reflects both red and far-red light, increasing not only red light but paradoxically the relative levels of far-red light.  Theoretically, this shift would cause tomatoes to put more resources into fruit production, and indeed some studies found this to be the case.

Unfortunately, the phenomenon is not consistent throughout repeated field studies.  Some of the other confounding factors are soil temperature (warmer temperature = more growth), insect and disease pressure (both decrease tomato production and are variably influenced by mulch color), and the fact that ethylene production (the plant growth regulator responsible for fruit ripening) is not controlled by phytochrome at all.

So are Tomato Automators worth the trouble?  Probably not, especially if you have many plants requiring many automators.

Friday puzzle solved!

Lots of brainstorming over the weekend, and all the answers were legitimate.  A few people came close with the observation that the roots looked like they had grown over something.  And that’s exactly right:

This is a great example of nurse log decomposition.  When the tree on the right first began growing (and it could have been decades ago), it sent lateral roots out, over, and around the nurse log to reach the soil.  As the nurse log degraded, the tree’s roots were left high and dry, outlining the girth of the original log.

Does this natural example have application in managed landscapes?  Absolutely!  As several of you pointed out, removal of soil or organic matter by erosion or decomposition can leave woody roots exposed.  If these roots are injured by feet or tools, they can lose their bark and become open to disease or pests.  These are the structural roots of the tree, and if their stability is compromised, so is that of the tree.

(Though this tree has had some injury to its roots (probably from hikers), it’s unlikely to fail as it’s pretty small. )

Friday puzzle

Finally – something else to do rather than post to the IAL blog!  On to today’s photo (and I apologize for its blurriness).

The tree in this photo is alive, and as you can see has structural roots perched well above the soil.  How might this have happened?  There are multiple possibilities.  And secondly, is there a negative impact on the tree, and if so, what?  Answers and another photo on Monday!

Have a nice weekend! 

Two new postings on compost tea efficacy – and safety

We just don’t have enough excitement on the blog, so I thought I’d bring up two new items that just crossed my virtual desk.  The first is today’s Garden Rant posting from Susan Harris.  I won’t spoil her well-written blog, but if you’ve been following the debate on the disease-control properties of compost tea, you’ll be interested in reading it.

The second was in an email from a colleague at the EPA on a new journal article.  Here’s what he said:

More potting soil and Legionella, this time in Scotland.  (Eurosurveillance, Volume 15, Issue 8, 25 February 2010).  Note that “other countries where L. longbeachae outbreaks have been reported” includes the U.S. but there is no required labeling here, though it is in Australia, New Zealand and possibly much of Europe.  Also note the association of Legionella mainly with droplets, and the possible connection to compost sprays as seem popular among do-it-yourself pesticide makers.

“The exact method of transmission is still not fully understood as Legionnaires’ disease is thought to be acquired by droplet inhalation. The linked cases associated with compost exposure call for an introduction of compost labeling, as is already in place in other countries where L. longbeachae outbreaks have been reported.”

The No-Work Garden Book

Occasionally one of the GPs will blog about a book that’s particulary good – or not.  I was given a copy of Ruth Stout’s No-Work Garden Book a few years ago and frankly hadn’t given much more than a passing glance.  But last week I thumbed through it and was immediately struck by the quality of science this self-taught gardener brought to her writing.

Much of Ruth’s gardening practices included the use of organic mulch on vegetable gardens, and she regularly wrote to scientists to ask for their interpretation of “expert” advice.  Here’s an excerpt from a letter written 50 years ago by Dr. Arthur Pratt from Cornell:

“Yes, leaves, hay, straw, etc. that are not decayed or that are only partially decayed will rob the soil of nitrogen if they are mixed into the soil. But when used on top the way you use them, I have never seen a nitrogen shortage as a result of the mulch.”

So, we’ve known for at least 50 years that organic mulches don’t cause nitrogen deficiencies.  Why does this misconception persist, especially for woody mulches?

Ruth also challenged the use of plastic mulches, then relatively new to the garden product market.  She understood the benefits of a no-till approach to maintaining healthy soils.  She has a whole chapter entitled “Make Mine More Mulch.”

So here’s to Ruth Stout, the original “Mulch Queen.”