When you water them, SOAK them thoroughly and slowly, don't sprinkle a bit every day.

Mulch the ground thickly - water when the soil is barely damp under the mulch.

And yes, they tend to curl when hot.

It's been hot as hell here too for the last 6 days, and very humid too. I STILL haven't had to water a single time yet this season. We get rain about every 3rd or 4th day. So far. But, with the temps up in the 90s, I have noticed a little leaf curl now. I went out today and thought I would probably have to water, but, after sticking the moisture meter in the ground, the soil is still 'wet'. I am positive I watered way too much last year (my rookie year).

Make sure when you do water to put the hose at the base of your plants and try to not get the leaves wet. We put in a soaker hose this year and mulched heavily over it, but so far we've only had to use it once.