Could be root rot.
Punch extra holes in the sides of that pot for improved drainage/air flow and monitor what times of day you see wilt. Does placing a dome over the plant cause it to perk back up again?

You MUST let the soil become rather dry between waterings or you will see wilt symptoms from not enough oxygen getting to the root zone.

Edit: That last plant actually doesn't look sick to me. Is it FLOPPY (doesn't look it) or just have a general shape that makes you think it's wilted?
stinkyattic Reviewed by stinkyattic on . My plant is out-growing itself. :eek: I NEVER though I would see this. - My plant is growing too fast. - Or, my roots aren't growing fast enough. An aggressive regimen of Wet Betty and Growth Excel has made one plant out-grow it's own roots. These plants are 19 days old. You can see from the first picture that it is my *suspected* Granddaddy Purple plant - the last one on the right. Picture 2 is of one of the other 3 "normal" ones - taken at the same time. *Keep this in mind, look at how healthy the plant in pic. 2 Rating: 5