Hello, this is my first time overwintering several potted forsythia and heucheras in an unheated garage. I want to “force” them to bloom late April for a nice container effect by our front porch. These potted plants seem to be ready to bud already (January 2) I assume due to the warm weather since October. Also the soil is dry, should I water them or will that only increase the chance of budding too early? Or should I place them outdoors where it’s colder to “slow them down”? If the temps outside drop severely I could take them back in the garage for protection. Any advice appreciated! Looking forward to Spring!!
Thank you for contacting Toronto Master Gardeners
Our website has extensive information on overwintering perennials in pots. You have a shrub and a perennial. Both are very different plants. Our website provides basic information on pot size and location that you may use to make decision on the two different pots: Overwintering Perennials
Insulating round pots – Toronto Master Gardeners:
https://www.torontomastergardeners.ca/askagardener/overwintering-shrubs-and-perennials-in-pots/
As you have not provided a photo or advised of the size of pots your perennials are currently resting, or the size of the plants, the information on when to start bringing them inside the house will be an assumption. You can bring in the Forsythia inside the house at least three weeks before placement in April. Forsythia with buds ( you did mention your forsythia has buds, if the plants do not have buds they will not have blooms) will bloom once inside a house in a sunny warm window. You will need to start watering the forsythia once it is inside the house. I bring forsythia branches with buds inside the house every year and place the branches in water, depending on the how much sun, heat and water, it can take 10 to 15 days for the forsythia to bloom.
You do not mention the variety or type of heuchera: As a native perennial it does not overwinter well in pots. Heucheras are shallow rooted, required good drainage (they die off in clay soil as they do not like to sit in water) The leaves in our climate can become quite ragged and should be removed leaving a crown. You can try to bring indoor to break dormancy in early March. It may not survive the winter or the indoor climate in a pot. Here is information on heucheras and potting up heucheras : https://www.youtube.com/watch?v=I7tIO-w9nOo
https://www.youtube.com/watch?v=kscxpQ4sdME&t=632s
Good luck with the April planter.