I am in Toronto and I would like to control the spread of some common and glossy buckthorn bushes. I enjoy pruning and I would like to prune the bushes, as close as possible to the ground, twice a year, in spring before any leaves appear and in fall. I would also prune or pull up(?) any new small shoots which appeared. I understand that buckthorn seeds can remain dormant in the earth for up to five years. Would continued pruning eventually kill the roots and the plants by stopping photosynthesis? I would be happy to continue pruning for years if necessary.
Controlling (or, ideally getting rid of) these invasive buckthorns will require persistence, and could take a few years. Pruning them to the ground is a great first step, although stems tend to re-sprout and as long as roots survive and spread, new plants can pop up. Buckthorns tend to establish deep roots quickly, and lateral roots can be up to 3 metres long. So a large part of the solution here is “root out the roots”.
Additional strategies to get rid of or control the shrubs include:
- Pull up small plants/seedlings when the soil is wet. A good time to pull is the autumn (mid-October to mid-November), to minimize disturbance to nearby desirable plants, which should have gone dormant by then.
- Dig out larger plants, be sure to get as many roots as you can, to prevent the plants from re-sprouting. You likely won’t be able to pull out all the roots, but continued vigilance for seedlings will help control spread.
- When you pull/dig buckthorns, disturb soil as little as possible, as open soil can promote rapid re-invasion by these plants.
- Both male and female plants have flowers, which appear from late May to early September.Female plants produce pea-sized berries that change from green to red to dark purple as they ripen, and can be seen from July through September. As birds love the berries – and spread the seeds inside – be sure to get rid of the berries when you see them. You are right, common buckthorn seeds survive for 2-6 years in soil, and glossy buckthorn seeds for up to 5 years.
- As with other invasive plants, the buckthorn waste (including berries) should be discarded in garbage, not composted or put in green bins.
- Finally, be careful – beware of thorns – wear heavy gloves.
One issue that some gardeners might have is to clearly identify the invasive buckthorns. Three look-alike buckthorns grow in Ontario. The 2 you mention are invasive plants: glossy buckthorn (Frangula alnus, formerly Rhamnus alnus), European or common buckthorn (Rhamnus cathartica). The third is the (desirable) non-invasive native shrub, alderleaf buckthorn (Rhamnus alnifolia). For descriptions of these look-alikes, and other species that can be mistaken for the invasive common buckthorn, see the Ontario government’s Invasive common (European) buckthorn. Best management practices in Ontario.
You have your work cut out for you (no pun intended) – all the best in getting rid of these nasty shrubs!