Misadventures in the blueberry patch

There's been a death in the garden. Our green thumbs have been done in by the blueberry bushes. We don't know if its because we used too much fertilizer or too little. Or if it's because the weather was too hot and then too cool. The adventure started out well. As soon as we got the twiggy starter plants into their pots in early April, they began to thrive, adding shoots, growing green leaves and looking healthy.
The first sign of trouble came suddenly. On the first 90 degree day of the season, a few weeks ago, our Chippewa bush burned to a crisp without so much as a warning. That morning it was green. That evening, it had turned brown and crinkly.
We called Miller Nurseries where we had purchased the plants by mail order and they were quick to send another bush. We planted it a over week ago, but so far, it has yet to sprout even a leaf.
Meanwhile, the Polaris seemed to be doing well. Until last weekend, when it too began wilting in the heat. I'm afraid it has since gone the way of its Chippewa sibling. In an effort to save it, Mitch replaced the soil, which ws heavy with a fertilizer specific to blueberry plants (they like it acidic.) But it appears the move was to no avail. He also ordered a PH tester from Miller, which has yet to arrive. It may give us an indication of where we went wrong. Either way, this is a pretty disappointing development. We may have to wait until the fall to try again. If any experienced blueberry growers have suggestions, please post a comment!