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What to do when invasive insects attack your garden

We have lost track of the number of times we have heard, “I lost my ash tree to the Emerald Ash Borer.” Major Canadian cities lost over eight percent of their tree canopy when this invasive insect moved through.
Autumn blaze maple. CONTRIBUTED

We have lost track of the number of times we have heard, “I lost my ash tree to the Emerald Ash Borer.”

Major Canadian cities lost over eight percent of their tree canopy when this invasive insect moved through. The result has been a vacuum where majestic, hardwood trees once stood.

Now what?

One lesson learned from this experience is to plant a diversity of trees. We should have learned, when the Dutch Elm disease decimated our American Elm population in the 1960’s, that it is unwise to plant monocultures.

We love ash trees for a variety of reasons: they are relatively fast growing without being space hogs (think Manitoba Maple), they grow straight, provide abundant shade, produce leaves late in the spring and drop leaves relatively early the fall and they are moderately tolerant of clay soils. They turn a brilliant yellow colour in the autumn, adding to our palette of fall colours.

What can you plant that would perform the same job?Here is our list of alternatives that might help fill the bill.

Autumn Blaze Maple. (Acer x freeman ‘Autumn Blaze’) A remarkable tree. A cross between the native rubrum and soft maple, it bears the best qualities of both species. Autumn Blaze grows fast, produces a well-balanced crown, is relatively disease and insect resistant and it is somewhat tolerant of clay soil. Best of all, its autumn colour will knock your socks off. Wherever a line of Autumn Blaze is planted, people stop and take pictures at their peak colour performance each October. Matures to 16 metres high and 10 metres wide. Not for small yards.

Little Leaf Linden(Tilia cordata) Fast growing and perfect for a medium sized lot. Mark has five large specimens in his 10-acre garden where they attract lots of nesting birds and provide dense shade, without the root-competition of many other deciduous trees, like Norway Maple. You can grow many shade loving perennials under a linden. Mark has lily of the valley, lamium, hosta, boxwood and yews thriving under his. Matures to 12 metres and eight metres wide.

Ivory Silk Lilac(Syringa reticulata ‘Ivory Silk’). This is a dramatic departure for the ash lover as it does not grow as fast or tall and it flowers dramatically every June around Father’s Day. But then, that might be just what you are looking for. Unlike other lilacs, this one does not feature heavy fragrance, or any fragrance at all. It is insect free and fills in a small space about 5 metres wide very nicely. Hardy to Edmonton, zone 2, so it is well equipped for winter.

Sugar Maple(Acer saccharum) This is Mark’s favourite, but it requires space. The new cultivars are more pollution resistant than the original species tree and they are moderately tolerant of our clay-based soil. Plant on an incline, allowing water to run away from their root zone for best results.

City trees.

While we are on the topic, it is important to note that almost half of the trees in major cities grow on public property. There are efforts underway to replace the lost ash. But let’s face it, there is constant pressure on government budgets everywhere to reduce expenses and spend tax dollars responsibly.

On that note, trees fit the bill very well. The TD Economics‘Value of Urban Forests in Cities Across Canada’ study of urban trees states that for every dollar spent on tree planting and maintenance, $1.3 is returned. We like making 30% on our money, how ‘bout you?

The point of course is that we cannot let up in our efforts to encourage government at every level to continue to invest in our urban tree canopy.  And a good place to start might be in our own back yard.

Mark Cullen is an expert gardener, author, broadcaster, tree advocate and Member of the Order of Canada. His son Ben is a fourth-generation urban gardener and graduate of University of Guelph and Dalhousie University in Halifax. Follow them at, @markcullengardening, and on Facebook.



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