Why I’m Getting Rid Of My Boxwood Shrubs
(Photo: Getty Images)
A lot has changed about my approach to gardening—and life—in the nearly twenty years since I moved into my house. I used to garden purely for aesthetics, planting boxwood shrubs—an evergreen species introduced from formal gardens in Europe and Asia—in a failed attempt to lend my dilapidated front lawn some grandeur.
But my growing appreciation for nature, birds and biodiversity has meant learning about how native plants benefit more than just my curb appeal—they offer essential food and shelter for the animals and pollinators that have evolved along with them. And as my garden grew wilder, I questioned those long-ago planted boxwoods—they didn’t seem to be doing much for birds or pollinators. They also didn’t thrive in my yard, growing spotty and yellow despite regular watering and mulch. My neighbours were having similar problems, with visibly ailing boxwoods vanishing from at least one front lawn on my daily dog walk. I didn’t think much about it until I read a story in my hometown newspaper, the London Free Press, about how the city is removing the boxwoods in a prominent park and won’t plant any more due to box tree moths, an invasive species that targets the shrubs.
So were my boxwoods also victims of the spreading pest? Here’s what I found out about boxwoods, box tree moths and whether or not you should rip out your shrubs.
What is the box tree moth—and where is it found in Canada?
I spoke to Javier Maldonado, the acting manager for the horticulture section at the Canadian Food Inspection Agency (CFIA), which has been monitoring the box tree moth since it was first detected in Canada in the GTA in 2018. Originally found in Asia, the pest spread quickly through Europe into the U.K., and it’s now found in Ontario, Quebec and in the Atlantic provinces, as well as in the northeastern U.S.
The moth feeds almost exclusively on the boxwood plant. “It is pretty devastating,” Maldonado says. “Its larvae eat the leaves and they are voracious—they tend to remove all the leaves from the plant and then start to eat the bark.”
And, because the moths can fly five to 10 kilometres in a year (and even farther with wind), it’s prone to spreading, Maldonado says. “If your neighbour has it, it’s quite likely your boxwoods will become infested too.”
Do box tree moths target anything other boxwoods?
No.
How do you know if your shrubs are affected by the box tree moth?
Box tree moth infestations can be hard to spot at first, says Aruna Panday of Toronto Master Gardeners. If you look closely at the plant and see caterpillars, or webs, that’s one sign. (Note that webbing can also be from spiders, which are harmless to boxwood shrubs.) Another way to check is to shake the boxwood like you’d fluff a pillow and check if moths fly out. Toronto Master Gardeners has more on spotting the moths in its helpful guide, and you can find photos of the eggs, the larva, caterpillars and the damage they cause via the CFIA.
Can you treat a box tree moth infestation?
Yes, but it’s a fair bit of work and there are drawbacks to consider. You can use BTK, a biological insecticide that targets moths. While it’s not dangerous for people or pets, it can be harmful to beneficial insects, including other types of moths. BTK is available as a powder, which can be mixed with water and sprayed over the plants. This should be done between early May and mid-June,mid-July or mid-September, when the boxwood larvae are present. It’s crucial to make sure you’re only spraying the larvae, not the moths, as BTK won’t kill eggs, pupae or adult moths.
One treatment doesn’t mean you’re in the clear—because the moths are now present in large areas of Canada, reinfestation is possible. Whether or not you can save your boxwoods is also a matter of how much damage it has already sustained.
Should you remove your boxwoods entirely?
If you decide to go this approach, Panday recommends sawing the shrub down first, cutting it off at the base, then digging out the roots using a shovel or pitchfork. “If you water the soil first, it’s easier.”
How should you dispose of affected boxwoods?
When handling boxwood shrubs affected by box tree moths, put them in a garbage bag and throw them out. Do not compost them.
My boxwood isn’t thriving—is it because of box tree moths?
Not necessarily! It could be boxwood blight, a fungal disease that’s also spreading across Canada—infected leaves turn brown or yellow before dropping off. Treating boxwood blight requires either cutting off the affected leaves, using a fungicide, or both.
“Another boxwood pest is the boxwood leafminer,” Panday says. “The leaves will look swollen or bumpy. If there’s not a lot of infestation, cut away the leaves. Insecticides are only helpful before the adults can lay eggs—here you're trying to kill the adults.”
Should I avoid planting boxwoods?
It depends on what you want from your garden—and where you live. “Box tree moths are not currently present in British Columbia or in the Prairie provinces,” Maldonado says. (If you’re in B.C., Manitoba, Saskatchewan or Alberta and think you’ve spotted box tree moths, report it to the CFIA.)
Panday suggests considering plants and shrubs that benefit pollinators and animals, like migrating birds. “It’s really important to think about your environment. Why is it important to have these really controlled hedges, rather than planting something that is not only aesthetically pleasing, but beneficial to the environment?”
What are some alternatives to boxwood?
Panday recommends the ilex glabra, commonly known as the inkberry holly, which is native to North America. “It has a similar look to boxwood, and dense foliage, which you can trim into hedges.” It also provides food and shelter for pollinators.
It’s still not certain what was wrong with my boxwoods—Panday thought it could be blight after I described the issue to her—but I have dug out some and am working on removing the rest. I’ve planted snowberry in their place, another North American shrub, because I read that birds go crazy for it. Right now, it’s sprouting pretty pink flowers; later on they’ll become the white berries that give it its name. It’s not green all through winter like boxwoods but, to me, it’s beautiful.
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Born in London, Ont., Gillian was Chatelaine’s former deputy editor, digital. She has also worked at Toronto Life and the National Post. Gillian cares deeply about fighting climate change and loves birds, sad lady singers, bikes, baking and wide-legged denim. She lives in Toronto's east end with her partner, two children and Rosie, her very exuberant Bouvier des Flandres.
