I have planters with combos of geraniums, petunias, and calibrachoa ready to go onto my balcony. I live in a Toronto condo, on the 9th floor. When is it safe to put my flowers outside?
Thank you for contacting the Toronto Master Gardeners. Your question is on the minds of many gardeners right now. This is a tricky time of year when a few warm days can be followed by unseasonably cold temperatures, making it difficult to decide when to move tender plants outside. A general recommendation is that tender annuals can be planted out when night time temperatures are consistently above 10ºC. Although our daytime temperatures are becoming warmer, overnight temperatures are still in the single digits. The ‘last frost date’ in Toronto is somewhere around May 4th, however, you can find dates ranging from April 30th to May 20th depending on the source. It snowed on May 9th in 2020!
Your situation is further nuanced by being on the 9th floor where conditions may be different (cooler) than at ground level. Temperature, wind, moisture and sunlight are all factors to consider in your space. For example, an exposed, windy spot in shade is harsher than a sunny, protected corner next to a warm brick wall.
A further consideration is acclimatizing your plants to the outdoor conditions. Plants coming from a Nursery or Garden Centre will have been ‘hardened off’ already. But if they spend days or weeks indoors before planting outside, a gradual re-introduction to the new environment will help to prevent stress and improve your overall plant health. The hardening off process is explained in this Toronto Master Gardener Tip hardening off plants
Having said all of this you are safest to wait another couple of weeks before setting out your balcony planters. If they are easily moved, you may be able to start the hardening off process in the daytime before then. Follow the weather forecast and remember that your balcony climate may differ from what the forecast predicts. If you are interested in further reading about balcony gardening, these references may be helpful Blooming our Balconies, Balcony Pelargonium (Geranium).
Best of luck with your balcony garden this season!
May 5, 2021