I read online that they do better down here in fall/winter, but in the past I've always planted them in the spring and they usually lasted until around this time of year; figured it was the cold that did them in, but if not, I'd like to have some flowering in my shady area.

It might depend on where in 9b Florida you are located and whether you get frosts and/or freezes in your area. For instance, I think zone 9b along the gulf side of the state is slightly warmer than 9b along the east side but zone 9b inland areas may experience much cooler temperatures during winter than right along the coast. Depending on whether you get frosts and/or the occasional hard freeze during winter, Impatiens may not survive. For light frosts they could be covered with frost cloth or a light blanket or sheet and possibly be okay but if you were to have two or three nights of temps near freezing or below they might not last long.

My husband and I lived in the Daytona Beach area for 43+ years and many years ago I grew Busy Lizzy (Impatiens walleriana) that survived a few years until one winter we had a frost and I'd forgotten to cover them and every few years or so we would have a hard freeze that killed a lot of plants. The New Guinea Impatiens (Impatiens hawkeri) aren't quite as dainty and can take a little suna but I think it just all depends on mother nature as to whether either of them would survive winter.

My sister and her husband lived in southern Broward County/Fort Lauderdale for many years and they couldn't keep Impatiens alive in the summer heat down there, so they grew them as winter annuals.

Impatiens busy Lizzie do fine in my garden, I'm in Central FL close to Sanford zone 9b. Mine are potted and so when we had two nights last winter that dropped to freezing, they were brought in my garage. They also reseed, mostly other potted plants have impatiens around the bottom of other plants, looks nice. New Guinea do great also, they seem to take more sun. Be careful not to do too much overhead irrigation. Mine look good all year long, under trees in filtered shade, a bit of morning sun. They can take temperatures down to upper 30's as long as no frost, they also do fine in 90 degrees, but can wilt if we haven't had rain, a quick watering will perk them right up. After a few years they get leggy, but have started lots of new plants by then. Plant then anytime you find them, best to keep them in the store pot for awhile, the roots are very fragile, I don't think I'd plant them right into the ground, unless you have rich soil. Place the pot down into the ground if you want them around a tree.

alpharalpha said: I've always planted them in the spring and they usually lasted until around this time of year; figured it was the cold that did them in...

Your reasoning seems sound to me.
Up here, the cold snaps usually finish them off.
In Fl zone 9b, I would expect the impatiens planted in a well mulched shade garden to get frosted back but not killed...
I often see the plants continue to grow back from the roots, if the ground hasn't frozen.
As far as planting them now?
I'd probably wait until late February or early March...

stone said: Your reasoning seems sound to me.
Up here, the cold snaps usually finish them off.
In Fl zone 9b, I would expect the impatiens planted in a well mulched shade garden to get frosted back but not killed...
I often see the plants continue to grow back from the roots, if the ground hasn't frozen.
As far as planting them now?
I'd probably wait until late February or early March...

Yes, might as well wait, mid-march is when I usually plant them. But next winter I'll try it out.