Shule, you are getting spring fever about now, huh! I've always planted my sunflowers out of doors but only at date of the so called last frost. Here it is Mother's Day, last year it was June.
Are you thinking of starting sunflowers in your grow room and then transplanting?
The only thing I could find was sunflowers do best planted as seed right in the garden. That is all I've known. But it takes a week to germinate and if there is a freeze, that will kill those little plants. They say 2 weeks before frost date but that doesn't make sense to me. I've never tried starts in the garden but I would imagine sunflowers as tough as they are would do just fine as long as you acclimated them from their grow room to the out of doors or green house.
I wouldn't plant until the frost date. I hate losing plants to a surprise freeze. Sunflowers are very tough but baby sunflowers not so much. Or use row cloth on top of your baby plants? That should work just fine.
Did you know THIS about sunflowers?
Sunflower seeds, leaves and stems emit substances that inhibit the
growth of certain other plants. They should be separated from potatoes
and pole beans. Where sunflower seeds are regularly used as bird feed,
toxins from the accumulated seed hulls eventually kill the grass
below. Harmless to animals or people, the toxins eventually biodegrade
in the soil.