Best Maple Ever?

The flowering trees look especially spectacular this year.  From the white lace of the native shad to the bright magenta of the redbuds, there is a colorful feast for the eyes on every hillside and in every neighborhood.  Perhaps even more impressive, but rather ominous, are the blooming Norway maples.  A bright yellow-green in flower, they promise to rain down bazillions of invasive helicopter-like seeds in just a few weeks time.  What seemed like the greatest tree going when imported by John Bartram in 1756 is now confirmed as an unfortunate mistake. 

Once proclaimed “the best maple we have for street use” and “one of the finest ornamental trees,” Norway maple today brings cries of derision from ecologists, a shrug of the shoulders by nurseries which still sell it, and blank stares from non-gardeners.  Where did all the angst, ambiguity and ambivalence come from?  Native not just in Norway, but in a broad swath all the way to the Caucasus Mountains, Acer platanoides naturally inhabits lowlands and river valleys, but has many characteristics which allow it to thrive far beyond its original territory.  It can survive, and often thrive, in darker shade than most other trees, and grow in mediocre soil and dry conditions, allowing it to inhabit many niches.  It blooms early, produces copious seeds annually, and spreads them liberally.  The seeds then germinate in high numbers.  It survives in smoke and air pollution, compacted soil, and around road salt.  When selecting a tough, easy-to-grow tree, our fore-gardeners found a good thing.  The hitch is that all this also makes for the perfect invasive tree, one that can jump the garden fence and run amuck, without a glance back over its lower limb.  Perhaps Norway maple is the Norway rat of the horticultural world.

All this is not to say that Norway doesn’t have problems.  This is a tree that is particularly prone to girdling roots, errant underground growths which wrap around and cause self-strangulation.  While sometimes easily visible at the soil surface, trunk cracking and straight or concave (rather than convex) lower trunk conformation indicate girdling roots are lurking down below.  Girdling roots are so common on Norway maples that it is probably more normal than not to see a large Norway maple declining due to this silent killer.

Then there is tar spot, a leaf disease which makes Norway maples ugly, but doesn’t cause them lasting harm.  Two summers ago, weather conditions helped create the perfect storm for this fungus to go on a rampage, and by August Norways were dropping leaves like a shedding sheepdog drops fur.  Since the hills of Troy are covered in Norways, the area looked terrible, and people grew distressed.  When the local TV news came calling, I had a difficult time acting concerned, since not only do I not feel bad when invasive weeds suffer, but I also knew that the trees would ultimately be fine.  Perhaps if we could reduce the Norway maple story to a soundbite, the public would listen.