European buckthorn in a GTA yard: why late autumn gives it away

Walk the back of the property in the last week of October and look for European buckthorn: a shrub that is still dark green while the maples, the lilac and the dogwood beside it have gone yellow or bare. Ontario lists it as a noxious weed, the GTA municipalities ask you to keep it out of yard waste, and it is far easier to deal with now, while you can still see it and the ground is still soft, than in May when everything leafs out together.

Buckthorn is usually the first shrub to leaf out in the spring and the last to drop its leaves late in the fall.

Why the last weeks before freeze-up are the time to look

Because the leaves give it away and the soil still lets go of the roots. The Ontario Invasive Plant Council's 2024 management bulletin says common buckthorn leaves stay green longer than most native plants, which makes it easier to identify into late fall and allows manual control until the ground freezes. Working then also disturbs less around it, since the neighbouring plants have already gone dormant.

Birds are the reason it turns up where nobody planted it. The province's fact sheet says birds and animals eat the black fruit, carry the seeds long distances and drop them, so a hedge line, the strip behind a shed and the gap under a fence are the usual places. The same fact sheet says it thrives in a wide range of soil and light conditions, so a shady fence line suits it as well as a sunny one.

1. Stand where you can see the whole back fence, side yards and any shrub border, and pick out every woody plant that still has green leaves.
2. Go to each one and look at the tip of a branch that is at least a year old. A short, sharp thorn at the end is the buckthorn sign the province gives.
3. Check the leaves: smooth, dark green, finely toothed along the edge, 2.5 to 6 cm long, set mostly in opposite pairs.
4. Look for clusters of small black fruit. They form in late summer and fall, and a plant that carries them is a seed source for the whole street.
5. Tie a strip of flagging tape around every confirmed stem. Once the leaves finally drop, a bare buckthorn looks like any other twiggy shrub.

Is it buckthorn or a native shrub?

Check the twig tip and the leaf arrangement together, because the province compares three buckthorns and only one of them is on the noxious weed list. The province's comparison chart separates them like this, and Oakville adds a warning not to confuse common buckthorn with native dogwood.

In a dry suburban back yard, a thorn-tipped shrub with toothed leaves in opposite pairs points to the first row. If you can't find a thorn and the plant sits in a soggy corner, compare it with the second and third rows before you cut anything.

What Ontario's Weed Control Act asks of the owner

"Buckthorn, European" is item 3 on the schedule of noxious weeds in R.R.O. 1990, Reg. 1096, and the province says it is listed because it can host oat rust and the soybean aphid, two problems for farm crops. Section 3 of the Act puts the duty to destroy noxious weeds on the person in possession of the land, which is presumed to be the owner. The same duty applies to poison ivy, covered in the post on poison ivy before fall cleanup.

Section 22 then narrows it. The duty and the inspector's powers to order or carry out destruction do not apply to noxious weeds far enough away from land used for agricultural or horticultural purposes that they do not interfere with that use. Glossy buckthorn, the wet-ground species, is not on the schedule at all. The regulation's own list of acceptable methods starts with pulling or otherwise removing the plant from the soil, and cutting the roots or stalks before the seeds ripen.

Which stems you can pull, and which need a different plan

Stem diameter decides it. The Invasive Plant Council puts the line for manual removal at about 5 cm across, on patches up to 300 square metres, which covers most residential yards. Wear gloves and safety glasses for all of it, because of the thorns.

1. 1Seedlings under 1 cmPull them by hand with gloves on. Plants up to about a metre tall can be pulled at any time of year, and the job is easiest the day after rain when the soil is soft.
2. 2Stems from 1 to 5 cmUse a lever-style weed puller, or dig around the base with a spade. Oakville says anything bigger than a seedling needs one or the other. Get as much of the root mass out as you can, because root left behind resprouts.
3. 3Close the holeTamp the disturbed soil back down or cover it with a thick layer of mulch. Bare, loosened soil is where the next crop of buckthorn seedlings comes up.
4. 4Stems over 5 cmCutting alone usually makes it worse. The bulletin warns that cutting without a herbicide leads to multi-stem regrowth from the stump. Its large-stem method is a cut-stump or basal-bark treatment with a systemic herbicide, and it notes that Ontario's cosmetic pesticides ban allows that only under an exception, with invasive plant programs carried out by licensed exterminators.
5. 5If you cut a big one anywayOakville suggests placing a tarp over cut stems to discourage new growth, and coming back to pull any sprouts while they are still small.

Go after the plants with berries first. The bulletin's strategy is to remove isolated plants and the heaviest seed producers, the female plants, before anything else. If a plant has to wait until spring, Oakville's fallback is to remove and destroy the berries now so it seeds nothing more this year.

Where the branches and berries are allowed to go

In the garbage, bagged, and never in a backyard compost. Every authority read for this post agrees on that, and the berries are the reason: they carry the seed, and the bulletin says seed can stay alive in the soil for up to five years.

• Mississauga (Peel Region): the Region's waste sorter lists buckthorn among invasive plants and says to place them in a plastic bag, tie it, and put the bag in the garbage. It also says not to put them in yard waste or the organics bin.
• Toronto, including Etobicoke: all invasive plants, buckthorn named among them, go in a securely tied plastic bag set out as garbage, not yard waste.
• Oakville: the Town's invasive plants page says to dispose of them in the garbage, not the compost and not in natural areas.
• Burlington and Milton: Halton's curbside guide names giant hogweed among unacceptable yard waste and does not single out buckthorn, so follow the province's instruction for invasive plants and put them in the garbage.

With a big pile of branches, the bulletin offers one more route: strip off every fruit cluster, bag the berries for the garbage, and chip the bare wood. Chipping is safe only when the fruit is gone or the plant is a male that never bore any. The province's last instruction applies to everything here: don't discard it in natural areas such as a ravine or a park edge, where the seed takes hold again.

Fill the gap so it doesn't come back

A cleared strip with bare soil and a five-year seed bank will grow buckthorn again. The bulletin says control works much better when the area is replanted with native trees, shrubs and plants that compete with new buckthorn, and that follow-up removal of new growth is what finishes the job. Autumn planting has its own deadlines, covered in the post on fall tree planting and watering to freeze-up.

Plan on a short check every spring for a few years. Buckthorn leafs out first, so the same trick works at the other end of the season: in April, the first green shoots along the fence line are the ones to pull while they are still seedlings.

A handful of seedlings and a couple of thumb-thick stems is an hour with gloves, a spade and a box of garbage bags, and a job to do yourself. An overgrown fence line, a shrub border where buckthorn has grown up through the plants you want to keep, or stems past 5 cm are when it makes sense to bring in help, and to get the permit question answered before anything is cut.