i don't have much experience with bedding begonias (wax, semperflorens or tuberous for that matter), but rhizos and canes should NOT be in direct sun.

-ming

The fibrous rooted semperflorens group are fine in full sun here in the UK where they are frequently mass planted in civic displays. The larger flowered tuberous types are better planted out into dappled shade.

Peter.

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this is getting over my head here... there are 3 different types? I bought some at my feed store and I have no idea which group they were... But they sure were pretty. Is there some way to tell the differece?

lol. there are actually 8 different types! if you're interested, try the "virtual greenhouse" at the american begonia society site.

-ming

Here is a link that might be useful: virtual greenhouse

In your zone you can grow in direct sun. If you have a south facing area next a white fence which get hot afternoon sun, this may not be the ideal place, but even half or most-of-the-day in sun will be ok in zone4/5.

They plant the semperflorens in mass plantings in public areas here in full sun, and while I agree in a cooler climate it would probably be fine, I have yet to see any here that didn't look awful. In fact, I would say 'perfectly awful' lol! So for anyone who's reading this in a hot climate, please consider giving them at least a little afternoon shade.