Norway maples (Acer platanoides) have a bad rep in Canada and the U.S. these days and there’s no denying that they’ve earned it. Introduced to North America from continental Europe in the mid-1700’s, the tree’s impressive adaptability (see What’s Not To Love, below) made it first a desirable ornamental for gardeners and nowadays the dictionary definition of invasive.
Norway maples can take over a natural area and wipe out native plants in the process because, in botanic wonk speak, they have competitive superiority. Here’s why:
1. They grow fast–faster than companion native trees such as sugar maples.
2. They keep their leaves longer than native species.
3. Once they’re bigger than all their competitors, they cast a dense shade that makes it very hard for many native plants to thrive and the diversity of plants suffers significantly.
4. For a big tree (growing up to 18m/60 ft. high), Norway maples have a shallow root system inhibiting the growth of competing trees.
5. Their leaves have a natural toxin that can kill soil fungi and other critters crucial to soil health.
6. They’re prolific producers of seeds that wing through the air up to 165 feet away from the mother tree. Someone actually figured that out at the US Forest Service.
7. They’re even better at things like photosynthesis and “nitrogen and water use efficiencies”. Click on this link if you’re aching to know more about that.
Sounds like Norway maples are the deciduous version of Lord Voldemort, right? These trees have used their awesome powers to spread from southern Ontario across to Newfoundland and parts of southern British Columbia as well as the northwest and northeastern regions of the United States. In most of these places, the tree is now considered invasive, notoriously putting our beloved native sugar maples at risk among others. So why would you want to plant a Norway maple?
You may want or need to plant a certain kind of tree in your urban garden for the very reasons it does so well in the wild. Your tree may have to tolerate shade from buildings, neighbours’ trees, and established shrubs in its seedling stage. It may have to deal with soils compromised by all the nasty pressures of city living including compaction, pollution, and drought. The Norway maple, for better or worse, makes a great so-called street tree in the new urban ecosystem. When you think of all the reasons why you’d want to plant one…
…what’s not to love?
- It’s remarkably tolerant of any soil, including sandy and clay
- It’s OK with air pollution, including ozone and sulfur dioxide
- Though mature Norway maples prefer sun or part shade, the seedlings are very shade tolerant.
- They’re much more tolerant of drought than many native species.
So how do you sidestep that not-so-lovable habit the non-native Norway maple species has of out-competing native species in the wild? Go with the un-natural flow and get a Norway Maple cultivar. I’ll get this party started by suggesting A. platanoides ‘Medzam’, Norway maple Medallion™. Medallion is hardy to Canadian plant hardiness zone 4a and only grows to about 40 feet in height. It tolerates heat, drought and air pollution. In spring, its green leaves are tipped in bronze and then, after staying green until late fall, turn red and gold. But, best of all, this tree is seedless. This baby ain’t going to invade anything.
There are other Norway maple cultivar options that are virtually seed-free or produce far less seed than the original species. For instance, ‘Crimson King’, a maple with leaves that start out and stay a lovely maroon red throughout the growing season, is reported to produce less than 10% the amount of seed of the original species and, of that seed, less than 1% is actually viable.
Check out more nice and perfectly unnatural Norway maples in the post Research Shows: Some Norway Maple Cultivars Are Not Invasive.