I moved to Toronto last year and this spring there is a large corner of the garden where the attached plant is growing. It is very prolific. Can you help me in identifying it?
What you have in your garden is most likely garlic mustard, Alliaria petiolata, an invasive herb native to Europe which is classified as an invading species in Ontario. You are seeing it in its second year, when it produces flowers and hundreds of seeds. Stands of garlic mustard proliferate rapidly, as you’ve noted, and the seeds are easily dispersed. Garlic mustard resembles some other Ontario native plants and one way to identify it for certain is to crush it in your hands – if you smell a garlic-like scent, then it is certainly this invasive species.
The best method of eradicating it in a garden is by hand-pulling, and now is the ideal time to do this, before seed production and dispersal. Garlic mustard seeds can remain in the soil for many years, and soil disturbance can stimulate additional seed germination from that “seed bank”. You will likely have to watch this part of your garden closely and continue to pull out any additional plants that emerge. Identifying this weed in both its stages will also be helpful in eradicating it – In its first year, garlic mustard grows a low cluster of leaves shaped like a rosette while its root system develops. In its second year, it resembles the picture you attached.
Below is a link to a website that provides comprehensive information on this invading species.