Alien Invasion – We Have Buckthorn

Here at the Baie-D’Urfé Journal editorial offices we sometimes get asked for information on things people are concerned about or we are urged to “Do Something” on their behalf – usually that means spreading some information.

Recently we have been hearing quite a lot about Buckthorn and have been asked what can be done to stop the spread of this highly undesirable plant. One of our enquirers has been in touch with the Town Hall and was told (we paraphrase) that they don’t have the resources to do much at all so we are on our own for the most part. It’s present on town land and it’s almost certainly present somewhere in most of our gardens – this is certainly an alien invader. Rather like cockroaches, left to its own devices this shrub will try to take over the world. It was brought to Canada from the Old World as a robust hedging plant … it’s certainly that … but it escaped from captivity and now we have a problem.

Buckthorns grow aggressively and out-compete native vegetation for space, light, water and nutrients.

It was mistakenly believed that birds and animals benefited from eating the abundant fruit. However due to its laxative nature, wildlife get no nutritional value from eating it. The fruit has a cathartic (laxative) effect (note the species name ‘carthartica’) and is eliminated without digesting and get widely dispersed. Seeds stay viable up to 6 years on the ground.

The first step to successful buckthorn removal: Know your enemy! While not incredibly remarkable in any of its physical features, buckthorn is the only tree with all of the following characteristics:

  • It is a tall, understory shrub, or small tree, reaching up to 20′ in its maturity.
  • The base of the shrub often contains multiple stems and its bark is extremely flaky.
  • Nicking the bark will reveal an orange cambium or inner tissue distinctive to this species.
  • The leaves are arranged alternately, though sometimes oppositely, bearing a broadly elliptical shape and tipped at the end. The sides are finely serrated, or small toothed, and the texture is waxy. Because buckthorn leaves remain green even into late autumn, they are perhaps most easily recognizable at this time.
  • They have ‘thorn’ in their name because they carry wicked thorns on the stems and branches.
  • They produce black berries that are only eaten by birds in extremis when nothing else is available
  • It has no known enemies in North America other than you

One of the major problems with this plant is that the roots secrete chemicals into the soil that inhibit the growth of nearby plants you actually want to grow in your garden. This photo shows what happens when it gets out of control – nothing grows near it at all. There is an area like this in the Arboretum if you want to experience it in all it’s glory – you will find it in the south-eastern corner of Pullen’s Pasture.

So it has to go – if you find any on your garden, and you probably will, please start an eradication programme. Your neighbours will thank you and your garden will too.

Removing smaller plants
For removing seedlings and smaller, younger buckthorn plants, simple hand removal works quite well. Pliers or a small shovel may also be used. With immature seedlings, roots are not yet deep, so it should be fairly easy to get the job done. Remember to shake the soil free from the roots so smaller plants can detach and decompose.

For very young stems no more than 2 years old mowing the infested area in the early spring and again in the fall, after nesting season, will control the spread of buckthorn and eventually kill the plants and deplete the seed bank.


Removing larger shrubs
This is why you really want to get the plants out while they are small. For larger shrubs, simple hand-removal techniques are hard to use successfully. Dynamite is not an option, though you may be tempted.

Stems larger than 1⁄2 up to 2 inches in diameter can be dug up with a shovel. Start digging about 6 to 8 inches away from the stem completely severing the lateral root system from the ground. Pull out the whole plant and shake off excess soil to fill in the hole, tamp down loose soil. If possible replace the organic matter and leaf litter as well as any desirable plants. Single stems are easier to treat with this method than multiple stemmed plants.

One tried and trusted technique – though it takes time and patience – has been employed at the Arboretum. Simply “ring-bark” or “girdle” the stem and wait for the trunk and roots to die. Girdling involves removing a strip of bark including the cambium layer around the circumference of a tree or shrub. If the strip is too narrow or not completely cut through the tree will heal and survive. Without the cambium layer, water and sugars are prevented from feeding the top of the plant and it slowly dies. This method works best with single stemmed trees or shrubs with stems < 3 inches in diameter. If there are more than 2 trunks, the method is less effective and may result in basal sprouts.

Use this method in the summer after the leaves have fully developed or winter after leaf drop; not during the spring growth period nor in the fall when sugars are moving into the roots. Just above the base of the plant, remove a 1 inch wide strip of bark, including the cambium (green layer just under the bark), by cutting two parallel lines, about an inch apart into the stem or trunk. Be sure you are slicing through the thin cambium layer but not deeper than that. Bang on the strip between the two cuts with a blunt object like the back of an ax and pull away the strip. For stems less than 2 inches in diameter, the cambium can be killed with a torch by applying 5-seconds of flame in sections to completely scorch the circumference of the stem.

If the steps listed above are properly followed, the chances for successful buckthorn removal are high. However, because each buckthorn berry contains up to four seeds, seedlings may reappear despite your vigilance. It’s best to revisit the site to check for seedlings because they can remain viable in the soil for several seasons. Ideally try to get the buckthorn out early in the year before fruits appear.

Lets make 2019 the year of buckthorn eradication around the bay

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