big plant ... small pot.. and it wilts during the heat of the day ..

not enough available water ... during the heat of the day ....

water it in the morning ... i would not water until it runs out.. you are washing out nutrients ... i might also let it soak in a pot or pan.. to insure all the media is getting thoroughly wet ... sometimes it runs right out ... and doesnt wet it all ... if it floats in the pot.. then the media is very dry ...

your watering pattern sounds perfect.. if it were in the ground ... or a bigger pot .... but the small pot is not holding enough water .. in my opinion ...

ken

Petunias are a partial shade or full sun plant in moderate climates but they don't like excessive heat. I would say your climate is too hot for it so it wilts during the heat of the day but bounces back when it cools off. Your soil is probably wet enough even if it looks dry on top. Stick your finger in it and you will soon find out. If it feels wet then don't water. I agree with Ken that too much water at a time washes out the nutrients in the soil.

Just bear with the wilt. As long as it keeps blooming it's OK.

I live in a climate that has temperatures in the 20'sC with some days going as high as 30C. On those high temperature days the leaves on my snapdragons and petunias in my south facing flower bed will wilt in the daytime and snap back when it cools a bit. They never stop blooming so I chalk it up to the nature of the plant and because I love both plants I keep planting them in that bed.

oh... thanks for the advice. yes, I think i'll try to water more carefully or use the soak method and see if the poor plant does better. if not, maybe like Dow said, it's just the nature of the plant. it keeps blooming for sure, today i counted even more bloom like 12 or so flower, and more buds in progress...