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

I see the light!

Here’s the follow up picture from Friday’s puzzler:

As you can see, there’s a street light near the lower half of the maple. (I cleverly hid it behind the utility pole in the first photo.) The green part of the tree never received the message that days were getting shorter, since the street light is bright enough to interrupt the dark period necessary to initiate dormancy.

This is one of my favorite phenomena unique to urban environments. It doesn’t appear to hurt the tree, although the green leaves will die before the tree can scavenge their nutrients. If more of the tree were affected, I’d be more concerned.

Congratulations to Planting Oaks, who nailed this right off. And kudos to those thoughtful alternative explanations, all of which could logically have had an impact on color change.

Autumn color puzzler

Here’s a photo I took in Buffalo about 20 years ago. Buffalo, like many places in the northeast part of the country, has fantastic color changes in the fall. This maple seems to have changed its mind part of the way through the process:

What do you think caused part of this tree to retain its green leaves? Answer and another photo on Monday!

Inspecting nursery plants, part 1

I’m frequently asked to give seminars on selecting healthy plants at the nursery, especially trees and shrubs which can run hundreds of dollars. (Nobody seems to want a seminar on how to pick out a flat of petunias.) I routinely visit nurseries with my camera so I can record examples of good and not-so-good choices. What better forum to share these than on our blog? I’m also curious whether the problems we see in the Pacific NW are found elsewhere in the country, or in the world for that matter. So today we’ll hunker down on our hands and knees and inspect root flares.

The root flare (or root crown) is the point where the trunk meets the roots and should be wider than the rest of the trunk. The photo below shows this clearly:

In balled and burlapped trees and shrubs, you might not be able to find the root flare as soil and/or burlap cover the root flare. The tree below is burlapped far above its root flare:

Over time, many trees and shrubs buried too deeply will develop trunk rot. You can inspect for rot by gently peeling back the burlap from the trunk and looking for damage. Don’t worry, this doesn’t hurt the root ball or the trunk:

The tree in the above example already has some red flags – the presence of weeds on the soil surface suggests that it’s been in this pot for a long time. (And no, you don’t want to buy this tree.)
The most dramatic example of the problems that can occur is this weeping larch, which has been completely girdled by the rot induced by the burlap and twine around the trunk:

Lesson: It’s cheaper to wash your now-dirty pants than it is to buy (and eventually replace) a poor quality plant.

Mysterious tree failure exposed!

end about the tree failure question! Many of you zoned in on an important point visible in the two photos I shared. The tree’s base was obviously quite narrow where the trunk broke, and with the tree’s vase-like architecture this led to breakage. But why was the base so narrow?

Again, several of you thought about root issues, such as a restricted root zone, or possible damage to the lower trunk. Actually, it’s a combination of root and trunk issues, as this last photo shows:

Tree failure 3

What we have is a large circling root (you can see it at the soil surface to the left and right of the trunk) that has girdled the trunk completely and prevented it from growing in diameter. The trunk above this point continued to grow, eventually creating the instability that eventually led to failure.

This tree used to be the focal point of a small urban landscape. It was planted about 15-20 years prior to failure and obviously had poor roots. It irks me that the industry cannot figure out a way to (a) produce trees with decent roots and (b) plant them correctly. No wonder so many ISA-certified arborists are now recommending that people only purchase bare-root trees, so that these heart-breaking scenarios are avoided.

Congratulations to Jimbo in Australia for being the first to identify this particular problem, and honorable mentions to those of you who had logical and realistic diagnoses for tree failure.

(I hate to take pleasure out of the fact that girdling roots are a significant source of tree failure in Australia, but Jeff and Bert give me so much grief about root washing that I was starting to wonder if it was only the Pacific NW that was cursed with this problem. Guess not!)

Mysterious tree failure…

Here is this week’s plant puzzler. This mature tree just fell over one summer day. There had not been any significant wind, the soil was well-irrigated (but not overly wet), there had been no construction work or other root-zone disruption. There were no significant pest or disease problems. I’ve posted two photos from different angles, and will show one more photo on Monday. Why do you think the tree failed?

Seattle Chainsaw Massacre

In the spirit of the season I’m including some photos from our neighbor’s willow tree that failed a few years ago. The failure wasn’t unexpected, given the age of the tree and the lack of crown care it received. What’s truly scary is the “tree service” that came out to deal with the problem. Low bid wins again!

(And yes, I’ll post a puzzler as well. Two for one today!)

Here’s the willow after the crown collapsed

Rickety ladder + chainsaw = suspense!

Standing in the collapsed crown – no rope or other safety equipment

Look Ma! One hand!!!

And best (worst?) of all, the remaining trunk was just left in place. It quickly resprouted and now resembles Cousin Itt from The Addams Family.

Graft and corruption

It’s election season – but that’s not why I’m doing a blog on “graft and corruption.” Instead, let me back up and explain that today I gave a seminar on diagnosing urban tree death. One of my points to the group was the importance of knowing the history of a site – what species were selected, how trees were planted, whether there had been any major construction activity, etc. I thought I’d continue the importance of site history into today’s posting.

Here’s a photo of a street tree – a Prunus spp. (Disclaimer: I am not endorsing a candidate for Mayor of Seattle despite the appearance of a campaign sign in the photo.) It’s a healthy enough specimen, though possibly a bit large for this narrow planting strip:

Several years ago you would have seen a different tree in this same spot:

Now did this weeping cultivar somehow transform into an upright form? Let’s look at this second photo in its entirety:

This reminds me of my favorite childhood book on Greek mythology, which had a great drawing of Athena springing from the head of her father, Zeus. Yes indeed, we are seeing the scion of a grafted tree lose the battle to the rootstock. Rootstocks, by their very nature, are vigorous. If we revisit the first photograph again, this time a little closer, we can see all that remains of the poor scion:

Lesson: if you are using a grafted tree in the landscape, you need to keep the rootstock under control. Grafted trees are probably not good choices for low-maintenance landscapes.

Epicormic mystery solved!

Good morning (at least it is in my time zone)! And welcome to those of you who found us through Blotanical or another blog site. We love seeing the increased participation on our blog.

Since I am a teacher at heart, I was glad to see so much thoughtful discussion over the weekend. Many of you suggested that pruning for vehicular traffic was the trigger for this growth, and it’s true that removing large limbs or heading back branches will result in vigorous epicormic growth. But I cheated on the photo and cropped it above the point of interest. Here’s the entire photo of this tree:

You can doubtlessly see that dark line encircling the trunk just above the two branches with the shoots. Here it is close up:

Venturing around to the back of the tree, we can see the source of this line – neglected staking wire that has now been enveloped by the trunk.

What this wire has done is to girdle the phloem elements, which as you’ll remember from basic plant science, are directly below the bark and the cork cambium. Without functional phloem, nutrients from the crown can’t reach the roots. Since the two lower branches were spared this girdling, they can still transport sugar to the roots, so the tree hasn’t died. But now it’s directing resources (water and nutrients) into the lower branches, where the new epicormic shoots are forming a new, functional (albeit ugly) crown. In time, the original crown will probably fail; there’s already evidence that the trunk is dying:

What could be done with this tree? If the wire were removed or at least cut so that the trunk could pop it apart, there is the possibility that the crown could have been saved. But since the upper trunk already looks severely compromised, it’s probably too late.

As a sad update to this set of photos, the owners had a tree “service” (I use the term loosely) to remove all the epicormic shoots from the lower limbs! I will let you know when and if the whole thing fails.

Oh, and gold stars to all who participated in the quiz!

Quiz time!

One of the things we Garden Professors can do is give tests! And the nice thing is you don’t get penalized for being wrong. So this will be my inaugural Plant Puzzler.

Below is a photo of a tree with epicormic shoots on its two lower branches. Epicormic shoots are vigorous, upright branches that have more of a juvenile than mature appearance. They often appear when a plant has been stressed, perhaps by overpruning, or maybe the roots were damaged by construction:

So here is your test question. Why are these epicormic shoots primarily (if not exclusively) on the two lower branches, and not elsewhere in the crown? (You can’t see the top of the tree, but I promise there are no epicormic shoots up there.) And what evidence would confirm your diagnosis? While there is only one correct answer for this particular tree, let’s see how many possibilities you can come up with.

Answers and more pictures next week!

Wonderful wood chips

I’m in love…with arborist wood chips. These are not your beauty barks or other packaged mulches, but the chipped branches and leaves fresh from the tree crews. It’s a great way to keep this resource out of the landfill – and don’t even get me started about using this great mulch material for a “biofuel!”

I’ve written about wood chip mulches a lot, but thought today I would post some photos to show you how well they work in suppressing weeds and promoting growth in restoration sites. We published a paper on this in 2005, though we’ve been using them in ornamental and restoration landscapes for about 10 years.

Here’s a recent project: a wetland buffer enhancement was being installed in an area that was covered in Scot’s broom (Cytisus scoparius) and blackberry (Rubus discolor):

We had a brush cutter mow it to the ground, then put a foot of wood chips down. Later, we planted poplar, ash, willow and alder on the site:

We had to keep records, both written and photographic, for the county who monitors wetland projects. So we took photos every year at the same points for comparative purposes. Here’s what part of the site looked like immediately after planting and then after 5 years:

That’s not to say that we haven’t had to battle resurgent blackberries. They migrate over from the wetland itself (which we can’t touch) and tip root. But the increasing shade and competition from the trees has weakened their ability to take over, and the Scot’s broom has been gone for years.

So that’s one reason I love wood chips. I’ll do a follow up some week showing how they can be used in the home landscape.