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.

Should I boycott cypress mulch?

It’s hard to think of mulch as a controversial topic but, as with most things these days, we find people on both sides of an issue.  And, as with most things these days, some of opinions are based on substance, others are not.  In the southern U.S. some environmental groups are advocating a boycott of cypress mulch.

Cypress mulch is derived from baldcypress and pond cypress, which grow in ecologically sensitive wetlands in the Southeast.  Cypress wood is highly valued for is natural decay resistance.  Florida and Louisiana are the leading states for cypress harvesting for timber and other products.  In Louisiana it is unclear if cypress is logged solely for mulch but cypress harvesting for mulch does occur in Florida.  According to Dr. Jim Chambers, professor of Forestry at Louisiana State University and Chair of a governor’s science panel on forested wetlands in Louisiana, cypress mulch production is a sensitive issue.  “Many of our cypress-tupelo forests are in a severe state of decline. As you can imagine, these forests are very important to south Louisiana for many reasons. Areas permanently flooded, areas that are flooded for substantial parts of the growing season, and areas subjected to salt water input cannot regenerate. The amount of forested areas with these conditions continues to increase as subsidence increases, coastal wetlands are eroded by storms and human impacts on hydrology continue to degrade many sites.”

The inability to regenerate new stands of cypress is an important concern and calls into question the sustainability of cypress harvesting on these sites.  Chambers is working with environmental groups and others to develop a process to certify that mulch is produced from sustainable forest harvest operations

Another issue related to cypress mulch is a claim that is circulating in parts of Michigan (and perhaps elsewhere) that cypress mulch is linked to cancer.  I conducted a search of the National Library of Medicine and National Institutes of Health literature database ( on ‘cypress’ and ‘cancer’.  The only hits I found were related to studies looking at falsecypress (Chamacyparis) extracts for anti-cancer properties, similar to taxol.  The claims of cypress mulch and cancer may be an amalgam of the environmental concerns over cypress harvesting discussed above and concerns over use of mulch derived from CCA (chromated copper arsenate) treated wood, which is used for decking and other uses similar to cypress.  Research has shown that leachate from mulch containing CCA treated wood can have elevated levels of arsenic and metals above established health standards.

We all know Linda’s fondness for wood chips as mulch.  My personal favorite is ground red pine bark for its durability and natural appearance.  The key is to look for renewable mulch products that are locally sourced.

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!


My Least Favorite Pesticide

People often ask me about the most dangerous pesticides — the ones which they should be careful to avoid.  There are lots to choose from:  Di-syston (aka disulfoton) is really bad.  Rotenone has some potential problems that make it scary, as does copper sulfate.  But for my money the worst thing out there is something that isn’t even supposed to be used as a pesticide (at least not anymore) but which finds its way into our gardens thanks to recommendations from people like Jerry Baker:  Tobacco.

Despite its obviously “natural” origins, tobacco isn’t allowed by organic growers because of its drawbacks which I’ll mention below, but because it finds its way into so many “how-to” books it’s definitely worth knowing about this beast.

It’s easy to buy chewing tobacco, mix it with a little water, and apply it to whatever aphids or other insects that you see.  What’s even better is that tobacco really does work (just like Jerry says!).  In fact, for some things it works great.  For example, I’ve tried all kinds of barriers against slugs, and tobacco is the one that works the best, hands down — copper is kinda OK, diatomaceous earth takes a while but works fine — but man, tobacco really throws slugs for a loop.  Watching a slug try to go through a pile of tobacco is terrible (and yet morbidly entertaining!)  First, the slug approaches the tobacco at a snails pace (the snail is a close relative of the slug!)  Then the slug touches the tobacco….and then the fun begins!  The slug starts to move really fast — literally mouse walking pace — and then it stops — and then it shakes — and then it dies.  This all happens within four minutes.  The slugs in the picture below are all dead.

Despite my success I have a hard time recommending tobacco for slugs for two reasons.  The first is that it can carry plant diseases which can cause some major problems, and the second is that some dogs like to nibble at the tobacco — and they won’t let you know they’ve nibbled it until you let them back into the house (if you know what I mean)!

When a tobacco spray is used for insects the process is a bit different than just placing tobacco on the ground.  First, you mix tobacco with water, let it soak for awhile, filter the water out, and then spray it on the insects.  In the old days — the 1800s when this type of spray was popular — they would mix about a pound of tobacco with a gallon of water.  Jerry usually recommends much less.  The problem with recommending less than this is that at lower concentrations it doesn’t work nearly as well — but you really wouldn’t want to apply more because then the spray starts to get dangerous (because of higher nicotine concentrations).  So it’s a catch-22.  Don’t underestimate the toxicity of nicotine!  Also avoid underestimating the nastiness of the plant viruses that this stuff carries.

So what should you use instead?  A good insecticidal soap, or a spray with water are what I like to recommend.  If you must use something stronger then look for an insecticide with the active ingredient permethrin and follow the labeled instructions carefully (also make sure that the insect you want to control is on the label — if you can’t identify the insect you’re trying to control, or if that insect isn’t on the label, then don’t use a pesticide).  For slugs my favorite pesticide uses the active ingredient iron-phosphate.

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):

Heron's Glen-6

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.

The joys of arborizing!

It’s Holly’s day…but she’s off playing in a tropical paradise.  So because she seems to be of a sunnier disposition than I am, I’ll post happy thoughts today.

One of my favorite pruning techniques, especially for small urban landscapes, is arborizing.  This is a way of creating small trees out of large shrubs – and often, a large shrub is as much as a small landscape can handle.  Rhododendrons are common landscape plants here in Seattle, and the larger ones lend themselves beautifully to this practice:


As you’ll notice in this example, arborizing not only creates an aesthetically pleasing tree form, but also moves the crown away from vehicular and pedestrian traffic.  This protects the plant from damage and enhances access.

This also works wonderfully in landscapes where you would like to have layers of shrubs, rather than one massive plant.  Look at this Ceanothus:

Arborizing this shrub not only allows planting additional plants underneath, but also allows some light into the house (note the window in the background).

Fall is generally a good time to prune (after the crowns have gone dormant).  It’s easier to see trunk and branch architecture in deciduous trees, and generally places less stress on the plant.

If you’ve arborized shrubs before, which species work well for you?  Which ones not so well?

See?  I can be a happy blogger!