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.

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 (www.pubmed.gov) 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!

Building a better tree? Not in the long run!

One of the landscape tree production practices that drives me absolutely nuts is heading back trees in the nursery to create “columnar” specimens.  It’s easy to find examples of these in Washington state nurseries, like the pathetic oak shown below:

 

Aesthetics aside, let’s focus on how the tree responds to heading back.  The removal of the dominant leader encourages lateral branches below to become more upright; from these laterals, a new leader is selected.  This new upright growth habit is highly prized by many landscape architects and urban planners, as such trees fit more neatly into small urban spaces without interfering with vehicle and pedestrian traffic.  Sure, it works great for a few years.

Now let’s look at these trees a decade or two later.  Branches grow in diameter as well as length.  All of these acutely angled branches begin to grow into each other, creating bark inclusions:

 

What effect do bark inclusions have on the trees?  These fused branches are not strongly connected; in fact, they are likely points of branch failure.  As these branches become larger and heavier, they can create hazard situations if they are near people or property.  What’s happening here in Washington, and probably elsewhere, is that arborists must be hired to prune out some of these branches to reduce the risk of failure and injury.

 
This…most definitely will lead to this…eventually

I can’t understand why this practice is perceived as “building a better tree.”  To me, it looks like creating a maintenance and liability problem down the road.

Shoot your favorite ash

One of the biggest issues facing urban and community forestry in the eastern half of North America is the Emerald Ash Borer (EAB).  As most people are aware, EAB was accidentally introduced in Michigan some time in the late 1990’s.  By 2002 when the insect was found and identified, thousands of ash trees in and around Detroit were dead or dying.   Since then the insect has continued to spread, partly by natural dispersal but also by hitchhiking on logs and firewood. As of July 2009, EAB now occurs in 13 states and 2 Canadian provinces.  To date, researchers have not found any indication of resistance to EAB in North American ashes.  This includes green ash and white ash.  Based on our current understanding of the insect, EAB has the potential effectively eliminate the ash genus from North America, similar to effect of chestnut blight on American chestnut or Dutch elm disease on American elms.  To help stave off the demise of ash to EAB a veritable army of university and government researchers are conducting wide array of trials to identify chemical or biological controls that can save ashes.  Several insecticides can be effective but so far are only feasible for use on high-value landscape trees due to the cost of application and the need to re-apply treatments every 1-3 years depending on the chemical.

To help build awareness of the destructive potential of EAB and the impact of losing ashes in North America, I invite readers of the Garden Professor’s blog to share photos of their favorite ash.  Photos can be e-mailed to me @ cregg@msu.edu and I will post them on the blog.  Include any pertinent information about the tree(s).  To get things started I have included photos of ash trees surrounding the Gateway arch in St. Louis.  In the early 1970’s over 500 ‘Rosehill’ white ash trees were planted along the sidewalks in the park area surrounding the arch, which was completed in 1967.  The ash trees frame the famous ‘Gateway to the West’ and provide shade to cool visitors during St. Louis’s sweltering summers.  Unfortunately, the ashes may ultimately serve as a cautionary tale of the perils of monoculture in landscape design if they are lost to EAB.  The National Park Service, which manages the Gateway Monument grounds has begun to plant new trees from a variety of species.  However it will be years before those trees will be anywhere near the size of the existing ash trees.  To date, EAB has only been found in Missouri in an isolated outbreak in the southeast corner of the state but the insect has a firm foothold in Illinois and is moving westward. The ashes in the Gateway monument are being monitored for EAB and presumably the Park Service will begin treating the trees with trunk injections of systemic insecticide if EAB are detected in or near the Monument.
Ash trees frame the Gateway to the West

Over 500 'Rosehill' ash trees line the walkways at the Gateway National Monument

Take it all off (cue bow-chicka-bow-bow music)

OK, I know there are skeptics out there including many of my dear colleagues.  Though it seems that at least some of my photos are making an impression.  So here is another little photo tour through bare-rooting – this time with a bigger tree.

This demonstration was given at the 2006 ISA conference in Washington.  This is a good sized tree…

…that we plopped into a Rubbermaid watering trough after removing the burlap…

…and washed off all the clay.  It is deceptively easy to do.

Oh!  I almost forgot!  We put some duct tape around the trunk just above the burlap before we started this procedure.  Look where the tape ended up:

So there is another really compelling reason to bare root trees.  Had we not, this tree would have been planted 10 inches below grade.  But I do have to say the burlap made pretty patterns on the tree:

Another plus – with the clay gone, these trees are really easy to pick up and move around!

And it didn’t need staking once it was mudded in…

 

And it looked great seven months later with little to no maintenance and lives happily ever after.  The end.

Health care reform (of trees)

Nothing is more frustrating to a gardener than watching a newly installed tree or shrub slowly die.  In performing “post mortem” analyses on failed landscape plantings, I’ve identified four common errors that can be easily avoided:

  • inadequate root preparation
  • improper soil preparation
  • planting below grade
  • inadequate aftercare

This blog entry will be dedicated to the first point – but before I do so, we need to understand how nursery plant production has changed over the last several decades.

A brief history of propagation
Many years ago the only way to obtain young trees and shrubs was as bare-root plants.  Plants were field grown, then dug up during dormancy for storage and shipping.  Bare-root trees and shrubs are usually only available during a narrow window of time, but in general these plants are healthy and structurally sound.  Most importantly for our discussion, growers can see the woody root system of bare-root plants and cull those that are not well formed.

The development of containerized production methods meant that plants could be grown and sold year around.  When plants are grown in a production greenhouse, they are generally started in small liner pots and gradually moved through a succession of increasingly larger pots.  Ideally this is done before roots become potbound, or the roots are corrected when “potted up” (moved to a larger container).  What we found, unfortunately, in a study of nursery plant quality, is that root systems are often ignored in an effort to produce large quantities of plants quickly and cheaply.  It is not considered to be cost effective to examine and correct root flaws during potting up, so the entire root mass is moved into the new container.  Structural root flaws are not self-correcting and will become more severe the longer they are ignored.

Based on our study, as well as evidence collected by numerous researchers and arborists, it is apparent that poor root quality is a significant problem in containerized and balled-and-burlapped trees and shrubs, at least in this part of the country.  Therefore, we need to correct root flaws before installing woody plants into the landscape.

A quick intro to correcting poor root systems
Balled-and-burlapped plants have a clay rootball; despite its appearance, it is fairly easy to remove the clay simply by removing the burlap and twine and soaking the entire rootball in water.  You can facilitate the process using your fingers to work out the clay, or use a gentle stream of water (Figure 1).

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Figure 1.

Once the clay is removed the root system can be evaluated.  If you find woody roots that are circling, girdling, or in general not growing horizontally and away from the trunk (Figure 2), they should be pruned (Figure 3).  You want to develop an evenly distributed structural root system.

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Figures 2 and 3 – before and after

The pictures in this post are from my own Cercis tree, which I planted in April of 2004.  This is not a great time for planting, since Seattle has notoriously dry summers.  Nevertheless, that’s when I planted and as you can see from Figure 3, I had to remove close to 70% of the root system.  I mudded it in well (which eliminated the need for staking), mulched, and kept the root zone well rooted.  It sat for about 3 months and did nothing (Figure 4), except of course the flowers died quickly!.  In July it leafed out (Figure 5), and 3 years later had doubled in size (Figure 6).  It is now close to 15 feet tall and is in excellent health.  Given its initial root system, it’s doubtful it would have done this well without intervention.

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Figure 4 – April 04              Figure 5 – July 04               Figure 6 – July 07

(I have performed radical surgery on hundreds of tree and shrub root systems and have only lost one small shrub, whose root system is in Figures 7-8.  Kind of tough to prune something as fatally flawed as this.)

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Figures 7 and 8 say so much more than I can.