Tender evergreens and tropicals
These plants don’t require a period of dormancy. Examples include bay tree, rosemary, French tarragon, phormium, mandevilla, passionflower and jasmine. The goal is to slow the growth of these plants so they can survive indoors during the winter and be put outside again once all danger of frost has passed.
A few weeks before fall frosts are expected, gradually introduce plants to life indoors by moving them inside for half a day, working up to a full day over a week or so. Don’t wait until nighttime temperatures are only slightly above freezing—plants may go into shock and drop leaves. Lightly prune, if desired. Place them in the sunniest location you have and water sparingly but regularly over the winter; high humidity helps, too. Don’t fertilize until just before you reintroduce them to outdoor living.
Tender tropicals that grow from tubers, corms or bulbs
Examples include cannas, caladiums and elephant’s ears. The goal is to store the tubers so they neither rot from too much moisture nor dry out completely and die.
When frost kills back the tops of the plants, trim the stems to 10 to 15 centimetres from the base and gently dig up the tubers. Allow the tubers to dry for a day or two, then store them in vermiculite or dry peat moss in a crate or box; place in a cool, dark area, such as a basement. (Check websites or gardening books for more detailed instructions for specific kinds of tubers, corms and bulbs.)
Tender perennials most often grown as annuals in cold climates
First consider whether it’s worth your time and effort to maintain these plants over the winter; most are easily acquired at a reasonable cost in the spring. Examples include geraniums, coleus and impatiens. The goal is to continue growing these plants to use them again next year.
Trim back individually potted plants and place on a cool, bright windowsill or under grow lights. Alternatively, take cuttings of your favourites and start new plants indoors. By spring, they will be large enough for containers.
Balconies can be especially brutal for potted plants. Your best hope is to use large containers insulated on the inside with thick pieces of Styrofoam or fasten pieces on the outside during winter (bungee cords are good for this). If possible, move pots to a sheltered spot, out of wind and sun. Cluster them together with the hardiest plants on the outside and the most tender ones in the centre. For extra protection, wrap the huddled pots in a large tarp, but leave the top open for air circulation.