Growing Under a Norway Maple

(Question)

My friends have a Norway Maple in their north facing backyard (North Toronto, clay soil, medium moisture). They love the shade but are having problems growing plant materials underneath because of this tree. I think the main challenge is the grass area (for kids play) but the garden beds are also problems. I want to suggest sweet wood ruff as a ground cover, and maybe ferns, hostas and coral bells underneath. Any advice you can provide regarding grass and plant materials would be greatly appreciated. Thank you.

 

(Answer)

Thank you for writing on behalf of your friends, and very happy to reply, particularly as the Norway Maple (Acer platanoides) has been receiving very mixed receptions by urban gardeners, and city and woodland arborists, alike. The Norway Maple, native to Asia and Europe, is a very good looking, robust, deciduous, medium/large sized tree that thrives in poor soil conditions, and survives drought. These are huge assets.

While you’re suggesting very good options for shade-tolerant ground covers and perennials, the issues at hand are a bit more serious than this. As your friends appreciate, the broad, opaque leaves provide a particularly dense shade from very early in the spring, to very late fall. But, flip side of the coin, so much so that the tree literally prevents the sun’s ray from reaching plant life below. Further, the fall leaf drop creates an equally dense mat that resists natural composting, and, if left to lie, prevents light from reaching other plant life in the spring. Add to this the fact that the especially shallow root system hogs all available moisture, and nutrients, and your friends’ back yard problems are apparent: lack of light, water and soil nutrients. Plus, depending on the breadth of the tree, the drip-line on either side, and the width and depth of  their property, perhaps their neighbors’ problems as well.

The City of Toronto, not too long ago, planted Norway Maples on homeowners’ frontage: this has now ceased. The City has declared this species an ecological threat: in the city’s ravines and forests, the shallow roots of this invasive tree discourage surrounding plants from growing, most specifically, killing off native saplings.

This is why neither grass plants, nor ground covers, nor other garden bed plants will thrive under this tree. Regardless of your thoughtful suggestions for alternative plantings, their Norway Maple is the elephant in the room. At this point, contacting an arborist would be the very best advice: depending on their priorities, the tree could be bottom-pruned, thinned throughout to allow a bit more light to reach ground level — or removed altogether. If this might be the decision, their arborist could advise on a new tree planting that would better suit your friends’ wishes for gardening, shade and play areas.

Below are a few links that people can use to connect themselves to Ontario arborists:

City of Toronto: Hire an Arborist

Landscape Ontario: Arborists

Further reading on invasive species:

Tree Canada

Minnesota Dept. of Natural Resources