Do I need grow lights to grow the seedlings of such plants as pansies, browalia, lobelia, larkspur and sweet william? I would otherwise just put them on an east facing windowsill with foil below and behind them. I’m just wondering because if they normally grow in the shade, why would they need supplemental light?
Congratulations on your decision to grow your own annuals. You will save a lot of money and you’ll also be sure to have the plants you want.
You can try to grow the seedlings without a grow light, using the reflecting method, but you will probably not have enough hours of sunlight from an east facing window, which receives light only in the morning. A tell-tale sign of insufficient light is that the baby plants start to get leggy in their attempt to reach the sun.
Some websites recommend 14+ hours of light, which Toronto will not receive until the end of April. If your window faced south, you would have a better chance. Grow lights provide a steady, consistent light and can be adjusted to the height of the seed containers.
A good place to look for information would be the websites of the suppliers of seeds and growing materials .
I have attached a link to a Toronto Master Gardener fact sheet on growing annuals. https://www.torontomastergardeners.ca/index.php/factsheet/growing-from-seed-a-toronto-master-gardener-guide/
Here is a link to a past answer on grow lights.