We live in Toronto and spent our summer abroad this year. When we returned, we found an enormous (some 6 ft high), thorny, shrub- or tree-like weed growing in our back yard in partial sun. We are planning to remove it, although this may be somewhat difficult because it is huge, and it has substantial thorns. We would like to know what it is. Thank you!
There are various possible IDs for this plant, one of the most likely being Ailanthus altissima, also known as Tree of Heaven.I suggest this because of the rapid, tall growth of the plant over the summer when you were away, and because of the presence of thorns, and because of the ubiquity of this urban, invasive seedling in gardens, on roadsides, in concrete cracks. Please refer to this link on our website which describes the plant and its management along with a photo. Another response from our website on getting rid of this weedy tree is here.
If this isn’t your weed, please contact us again with more descriptive information about leaf, thorn size and location on stem, colour of bark, and/or photo of your tree. We’d like to ID it for you.
Other possibilities are Gleditsia triacanthus (Honey Locust) or Juglans nigra (black walnut), or Rhus glabra (Sumac). These all have compound leaves similar to Ailanthus. Another possibility is Rhamnus cathartica (European Buckthorn) which is a fast-growing invasive species that is more and more frequently seen in the Toronto area. Please click here for a description and photo.