Can a Rosemary plant in the garden survive winter in Toronto and how to protect it in winter? Thanks.
Rosemary or Rosmarinus officinalis, is a native of the Mediterranean region. It prefers full sun and a warm climate. While most varieties are way too tender to overwinter in Toronto, several varieties have been cultivated to withstand colder winters- up to minus 21 celsius, given adequate protection.
Rosmarinus officinalis ‘Arp‘, Rosemarinus officinalis ‘Madeline Hill‘ aka Hills Hardy Rosemary and R. officinalis ‘Nichols Select‘ are all varieties labelled USDA Plant Hardiness Zone 6, but have been known to survive Zone 5b conditions if they are protected.
Plant your rosemary in a sunny position with at least six hours a day of direct sunlight. Rosemary doesn’t like wet feet, so a good draining soil is essential. Find a sheltered spot, away from bitterly cold winter winds. Prune your rosemary back after the first frosts and then mulch heavily with a good 4-6 inches of coverage.
If you don’t have the right conditions or want to eliminate all doubt, bring the plant indoors for the winter. You will need a sunny spot, like a south facing window sill, in a cool room (around 18 c). Make sure you have a very quick draining soil mixture and water lightly, very occasionally. Standing your pot on a tray of fine pebbles and adding water to the tray is another way to provide humidity overwinter without overwatering.
Grow lights can be used to increase the daylight hours. Rotate your pot to give the plant even light exposure. The leaves may dry out and brown off, but don’t be tempted to increase watering until spring when shoots of new growth appears.
Its hard to predict how cold Toronto’s winters will get, so you can always hedge your bets and take cuttings from your outdoor rosemary late summer to sprout inside, for planting next spring.