Where I live, the first very hot days with driving sun cause my plants to wilt, both the potted ones and the ones in my garden. There are times during the summer when the prolonged heat can make them suffer. This tends to happen even if they've been watered deeply prior to the day's heat.
If you have an ice maker, you can place ice cubes at the base of your plants and they will provide a slow, cool drink as the sun rises. If you don't have an ice maker, you can fill plastic bags with water and freeze them overnight. Poke some holes in them and place them at the base of your plant(s) and again, they will provide a slow, cool drink.
This would obviously be a lot to do if you have some serious acreage, but for those of us with small gardens, especially patio gardens with potted plants, it's perfect. It's also great for newly-planted plants who need that extra bit of nurturing.
I have a lot of pots on my deck and in the hot days of summer I can easily sprinkle ice cubes in all the pots that need the cool down. 
