Using plant hardiness zones, we have added a green roof planting guide for Quebec and Eastern Canada. It is not a definitive list but gives members an overview of what plants are potentially useable in these areas.
The authors are not from Canada, We have have visited green roofs in Toronto, Vancouver and Calgary over the last few years. Therefore, we are reliant on help and advice from others. In the light of this, the list has been drawn up by GRT’s good friend Kerry Ross from Calgary. Kerry is a green roof designer and she speaks both English and French speaking Canadian . In North America plant selection is usually undertaken by referring to the plant hardiness zones.
The plants that are listed should be relevant to small scale green roofers south of the border in north-eastern USA as well.
Plant Hardiness Zones
A hardiness zone’s map the geographic areas that specific categories of wildflowers are likely to be able to grow. Being ‘hardy to Zone 10’ means that a plant will withstand a minimum temperature of −1 °C (30 °F). A more resilient plant that is “hardy to zone 9” can tolerate a minimum temperature of −7 °C (19 °F).
We don’t really use plant hardiness as a guide in the British Isles. Over 80% of the islands sit between 8a and 8b hardiness zones. However, it is interesting looking at the plant hardiness map of the UK. London sticks out on the map for it sits in Zone 9a. Obviously the urban heat island effect creates a warmer climate in London during the winter. This shifts it into the zone associate with the extreme south and wests coasts of the British Isles.
We will be hoping to add further plants lists for other parts of North America and the rest of the world over the coming months.