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P8090287.JPGWhen we are growing trees to send out to our research partners, or for study in our research nursery, we are looking to set a permanent canopy at around 12 feet. With the conditions most trees are growing in, they would be shrubby and around 7 feet tall. To get them higher, and keep them straight, we have a lot of methods, like pruning, staking, and tree therapy.

Tree therapy isn't really an official term. It is simply the bending of trees to get them to develop caliper and grow in the direction we would like them to. When you bend a young tree, you can almost feel the fibers inside of it breaking. When a tree bends and moves, it responds by growing stronger, similar to human muscles after exercise. This also occurs naturally, from the blowing of the wind. This response is called "thigmotropism," which I talked about earlier in relation to staking.

Tree therapy can be a tricky thing. If you bend too lightly, you aren't going to do much. If you bend too hard, the tree snaps. Either of these results doesn't help much. It takes quite a bit of practice to get it down correctly, and every once and awhile you will have a snapped limb.

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In the nursery, we are proud of all the trees. They all give it all they can, every day, rain or shine, sleet or snow. Sometimes trees die, sometimes trees don't make the cut, and sometimes trees are never even given a chance. That is just the nature of the work.

At the begining of the season, we notice a willow had germinated in the gravel pile that is going to top off our drainage ditch. We never got around to filling it up this year, and the willow steadily punched its way through the season, growing in terrible soil with zero attention from Team Tree.

Today, this brave willow is aorund nine feet tall. That is tree-spirational. That deserves the "Rocky" soundtrack. Gravel Willow, you are the Contender of the Season. Congratulations. We will probably put this tree in the rain garden, to help bioremidiate the soil, which is more gravel and chopped up elm trees. It has a rocky road ahead of it, but I believe in this tree.


P9280665.JPGChad next to the gravel willow "Rocky" marking it's original height this season

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At the beginning of the summer we began two European-style pruning experiments, Les Trognes, and Der Dachplatane. The trees will take quite a few seasons to develop, but the end results will be very interesting.

Thumbnail image for IMG_4004 (1).JPGFor some background, Les Trognes is a very common practice in European cities. We chose a non traditional species for it (poplar), so it will be interesting to see how it reacts. Les Trognes, also known as "pollarding," is the yearly pruning of a tree down to one point. This, over time, develops a nubby club of scar tissue with a large amounts of yearly sprouts.The large quantity of callus (woundwood) tissue allows pruning off all of the sprouts without having as much danger for decay and infection. Les Trognes should not be confused with topping, which is where important sections of the main trunk are removed at the top to satisfy height requirements. Les Trognes is a pruning method that requires annual care and does not remove important parts of the tree, topping is a dangerous method of making trees fit that removes important natural defenses. As the photo on the left shows, pollarding can produce old, healthy, trees, that are also quite small. This one is from my friend Andrea in Oslo.

The method was said to of originated in France, where a king, to control deforestation, 


decreed a maximum diameter on available firewood. Les Trognes then developed out of this, with people trimming trees down to a certain diameter every year for firewood and animal food. Eventually this became a very common sight. In the US, this is very unusual, and, outside of San Francisco, it isn't seen in urban environments. In a few seasons, hopefully ours can develop the Les Trognes look, right now it hasn't had time to develop sprouts (there one of them is on the right).

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Why are you attaching a stick to that tree?

Jonathan and I spent a day and biked over to the high bridge dog park. During the arbor day celebration we planted a bunch of trees there, and went to check up on how they were doing. As part of the checkup, we removed the metal conduit poles that had been attached to some of the trees. Someone asked what the poles did, and there are a lot of answers, dependent on how old the tree is and where it is in development.

For the high bridge trees, the poles are there to act as a support while the trees develop enough roots to support their own weight. When transplanting trees they need support while developing enough roots to support themselves. Once the tree has had some time to establish itself, the pole should be removed. The conduit helps the tree stand up, but also takes away the effects of the wind on the tree. When a tree blows in the wind, the force against it tells the tree to grow stronger. This is called thigmotropism, the growth response as a result of force, and is important for tree development. Stakes also can rub into a tree repeatedly, causing lacerations in the bark.

In other circumstances, staking a tree is used to train a leader. This is the branch that is headed most vigorously towards the sky. The leader is trained to keep the tree going upwards. Trees naturally have no intention of shading bikers, picnickers and others. They are most concerned with growing just tall enough and far enough out to grow and spread their seeds. In a forest they have the job of getting through the canopy, but in an open field or park, a tree has no reason to grow taller than around 6 feet. This is why through pruning, staking, and a lot of other work, shade trees grow much taller than they naturally would.

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Yesterday at the research nursery we had a unique and fun opportunity to do some pruning work with Louise Levy of Levy Tree Care in Duluth, MN.

Besides her work in Minnesota as an ISA Certified Arborist, Louise has had many opportunities to travel and work in France, Belgium, and Germany - studying and practicing pruning techniques and styles that are both very old and, in many cases unknown to American audiences.  We've been talking about "alternative" pruning and training practices for some time, we finally brought it back home!


Dachplatane - Before

One of the first techniques we experimented with is called Dachplatane, which means "roof tree" or "umbrella tree" in German.

While normally applied to a London Plane tree (Platanus x acerifolia) we tried it on a Northern Acclaim honeylocust; definitely not a direct comparison, but the tree was already moving toward this canopy structure - and additional work made sense!  One interesting and inspiring approach to this tree was Louise's desire to work with existing leans or bends (due to wind) rather than our typical "pull 'em up straight" mentality.  The resulting tree is interesting and should provide for many years of discussion and continued experimentation!

Dachplatane - AfterHere is link to a site Follow this link to a website showing the steps for creating Dachplatane (in German). 

This also shows the support structure used to create the "roof", which we have yet to install.

Tower Poplar - BeforeNow, moving on to pruning practices seen commonly in Belgium and France, we chose a "volunteer" Tower poplar (Populus x canescens).  This tree is a root sucker from a parent right next door and almost begged to join in the pollarding party!

Tower Poplar - After

Jonathan, one of our summer research assistants tested his saw blade with this foreign, yet exciting, method of pruning!

We'll be sure to continue the intensive and recurring pruning required to establish the callus/woundwood heads on this tree!

Black Alder - Before

Our final subjects included a couple European black alder that had severe winter kill last winter. 

Lacking their definitive central leader and upright habit these trees were great candidates for something new and different!

Black Alder - After

Using techniques usually described to create "Les Trognes" in Belgium and France, we brought these trees into a new light and hope to have many more years to follow their progress and continue their work.

PLEASE NOTE:  This should be considered experimental work for our region.  We are working with species not normally used for these techniques and are interested in testing their suitability for success! 

These pruning and training practices have undergone centuries of practice throughout Europe - but on native-European species that have a very long track record of success. 

We're testing local species and varieties, hardy to Minnesota and the Upper Midwest to track and test both their response and performance after this work.  Please check back often for more updates!


...and one final shot for inspiration!

Les Trognes in Paris (photo courtesy of Russell Kennedy)

Les Trognes - Paris

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Pruning Young Elms - Cover Promo.jpg

Elm Selection Guide
Green Bay Elm Guide - Varieties

Elm Pruning Tips

Green Bay Elm Guide - Pruning

Pruning Young Elms
  • book available at the WAA registration desk and at the Brown County Landscape Short Course ($12.00)
Book Excerpts

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Pruning Young Elms is still in print!

If you are interested in this book please contact Chad Giblin at:

Thumbnail image for Pruning Young Elms - Cover Promo.jpg

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Urban forestry and arboriculture has changed quite a bit over the last 100 years.

Many old practices like cavity filling and wound painting are gone for good. Oftentimes, though, we can learn from the old-timers, like Theodore Wirth.

Wirth & Co Photo - Calhoun.jpg

Wirth was appointed Superintendent of Parks in Minneapolis in 1906 and was instrumental in creating this "City of Parks".

In this photo we see Wirth (far left) and other Park Board Commissioners, posing with bare-root American elms.

Fast-forward 100 years to 2010 and we are applying pruning practices from this bygone era to trees in the 21st Century.

Craig - Theo Wirth.JPG

Craig Pinkalla, arborist with the Minneapolis Park & Recreation board, stands next to a Princeton American elm he's just finished pruning at Fort Snelling. 

Since his days maintaining the urban forest in the City of Milwaukee, Craig has been a strong advocate of giving young trees a chance to become mature, productive shade trees. 

In a sense, we've gone "back to the future."

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Chad - Smiley.JPGChad Giblin will be at the 48th annual Minnesota Shade Tree Short Course at Bethel University in Arden Hills, MN on 16 & 17 March 2010 signing his new book Pruning Young Elms and discussing structural pruning techniques for young elms and other popular trees in the urban forest.

Stop by for some great continuing education for arborists, urban foresters, and tree advocates.  A copy of Chad's book is included in the registration price for the Short Course.

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