I read that you should plant Dahlia bulbs until outside temperature reaches around 60F or about 16 Celsius. Can I get a head start by planting them in container indoor and next to the window?
Thank you for contacting Toronto Master Gardeners.
Dormant dahlia tubers are generally planted into the garden in early Spring; the rule of thumb is about one week before your area’s last frost date. The last frost date for Toronto is around May 9, with local variations influenced by distance from Lake Ontario and the micro-climate. They usually bloom 8-12 weeks after planting. If you want earlier blooms, starting them indoors is a great idea; in that case, transplant the actively growing dahlias into the garden only when all dangers of frost is past, as the plants are very sensitive to frost.
Since Dahlias are originally from Mexico and Central America, they are sun-loving plants and thrive in warm weather; but they are also surprisingly tolerant of cool, rainy summers. The key is to give them good soil, lots of nutrients, plenty of water, and did I mention as much sunlight as possible? They hate hot and dry, however, so if they are in a spot with full afternoon sun, then make sure they don’t get dried out, and perhaps even provide a bit of shelter from the harshest of the sun’s heat in summer.
We wish you the best of luck with your Dahlias.