Dianthus Amazon Neon Duo

Ok so this is liek the third year I have planted these, I have really sandy soil and they do great till about July when I go on vacation and its a million degrees and it hasnt rained in months. And I get back and they are fried. This year I planted them in morning sun only so we will see if that helps. If not, its all food I get to enjoy them for a few months from March to July so... much cheaper than my cut flowers. And the butterlies love them. Of all the freaking flowers in my yard that are supposed to attract butterlies, they are forever drinking from these and ignoring everything else in spring!!! What gives?