by Jonathan Fillmore
This week’s tree of the week is the London Plane Tree (Platanus x acerifolia). The London Plane Tree is a stately shade tree growing to a height of 70 feet tall. The mature bark is a stunning pale grey with exfoliating brown bark. The leaves resemble the look of a maple having a palmately lobed leaf. However, unlike a maple leaf, the London Plane Tree has a fussy back, giving it a unique character.
Being a zone 5 tree, The London Plane Tree is not commonly seen in Minnesota as it is not hardy to the northern climate. However, there are a few London Plane Trees scattered throughout St. Paul and Minneapolis. The slightly warmer temperature of the cities is often just enough for the London Plane Tree to survive the harsh Minnesota winter.
In the team tree fields, we have three varieties of London Plane Tree, Exclamation!™, Columbia, and Bloodgood. All three varieties grew extremely well this season! It was exciting to see the trees grow from small 4-6 foot whips to a sizable 1″ caliper trees. This fall, we dug out most the London Plane Trees to prepare to plant in root trapper containers next spring! The image bellow shows two of the four rows of London Plane Tree at the nursery. The lush, 12 foot strips of grass like plants growing in between the rows of trees are cover crop that team tree uses in all fields to keep the soil as healthy as our trees. The cover crop is a mixture of millet and buckwheat, both fast growing plants. The cover crop is used to maintain moisture in soil, reduce weed population, prevent wind erosion, and finally, increase soil organic matter. Often times, nurseries keep the soil bare by continuously spraying for weeds throughout the season to reduce the competition for resources. However, the benefit cover crop provides for the soil far out weights the marginal decreased caliper growth.
The vigorous growth of the London Plane Tree is quite typical for the tree. The London Plane Tree is often used as street trees in warmer climates due to the vigorous growth and ability to withstand high compaction and atmospheric pollution. The number of tough tree species for urban situations is becoming less with the loss of American elm to Dutch elm disease and the more recent loss of Ash species to emerald ash borer. Both American elm and ash trees were extremely common street trees due to similar tough qualities the London Plane Tree has. With fewer and fewer street trees to withstand the tough street conditions, it is important to test the winter hardiness of different tough trees like team tree is doing with the London Plane Tree.
by Nick Neylon
When 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.
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.
Chad next to the gravel willow “Rocky” marking it’s original height this season
by Nick Neylon
Arborists from Minneapolis and St. Paul came today to pick up the new city trees. The pot-in-pot field is almost empty now, we sent out 3 truckloads from there, and the container area is almost empty too. It was a long day of lifting trees, and looking around at all the dirt rings left, where my summer work once stood, I had a slight case of “empty-nest” syndrome.
Jonathan and I are going to bike out to Armitage neighborhood soon to help get these trees in the ground with the proper research conditions. We are going to be doing tests on the effectiveness of soil amendments, or putting organic matter in with the trees, not just the usual boulevard dirt, and soil rings, which among other things makes it a lot easier to water the trees.
by Nick Neylon
We have been running a research project for the past 7 years on the Olson Memorial Highway median in North Minneapolis. This is a true proving ground for urban trees. There are multiple lanes of traffic on either side, lots of salt spray from cars, large mowers on small spaces, and compacted soil to name a few challenges. This is not a friendly environment for trees, but it is just the place to do an evaluation on which trees work best in difficult urban environments
There are 147 trees going down the boulevard, almost a mile and a half of them in a line. There have been a few necessary replacements, and most trees show signs of wear, but beyond all the salt damage and mower slashes, there are quite a few trees showing promise of high, wide crowns and stable trunks. On the right, Chad is holding a long (7 ft.!!) basal sprout coming from a Cathedral elm, (Ulmus davidiana var. japonica). Basal sprouts can cause trouble for urban foresters and arborists. Nonetheless it is a good demonstration of the vigorous growth of elms and why they continue to be a popular tree in our urban forests.
The data collection took a whole day, starting and ending with a nice bike along the cedar lake trail (team tree gives it two thumbs up). Thankfully the weather cooperated and wasn’t blazingly hot, or extremely windy. It was the most pleasant trip we have had to that site, and that is saying a lot for 6 hours between traffic.