My hibiscus are wilting mid afternoon in the sun and partial shade

more water!! even the 'hardy' varities are not drought/heat tolerant .. water at night to give them a good head start for the day; just let the hose drip on them ....

make sure they have adequate WATER. If it's been raining every day and suddenly stops for a day or two, the plants thinks they're thirsty. Mulch around roots to retain moisture

I agree with all the suggestions above. I have mine in pots and they receive a thorough drenching minimum every other day when it is real hot out. I have a number in self watering pots and they empty out that almost gallon of water in one day no problem. They like their moisture, but at the same time don't like wet feet, that can cause root rot, especially since they seem to like being root bound. Mine don't like the afternoon sun so much, so mine haven't wilted yet this year, but when I had a couple last year that got the hot afternoon sun, they wilted a couple of times and weren't flowering like the others were that were in less sun, I moved them to where the others were and within a week they were putting out loads of flower buds and growing like a weed. Good luck with your hibiscus, Charlotte, they are such beautiful flowering plants!