I grew Penstemon digitalis, put them outdoors in January in 5" deep plug trays covered with row cover fabric. A pot and window screen would be similar. They had one of the best germination and survival rates of anything I sowed.

Thanks, Skip1909. That’s fantastic. Where are you located? And where do I get 5” deep plug trays? Is there anywhere online you can recommend?

Im in NJ but they grow in colder zones. I got the plug trays at the greenhousemegastore website but I've bought penstemons in 3.5 square pots that are 3.5" deep, so you dont need the deep tray.

Curious to know what kind of potting soil or mix you used.

Last year I used Vigoro potting mix from homedepot, which was bought while frozen solid in the middle of the winter haha