Azelea problems

[crab apple]

I'm not having much luck with azeleas. I'm not sure the variety, just Lowes or HD Azeleas but they seem to grow good around here. You can see them everywhere in ppls headges, They seem to grow great without much maintaints. Anways the last year or so I've tried to add some to my collection by giving them a pretty good cut back and root work at the same time. Most work done in the spring and most of them initialy survive and do well, even flowering. But eventually most seem to wither away. They're planted in everything from potting soil to Kanuma and they all seem to suffer eventualy. Lately some plants have had mealy bugs but it doesnt seem too hard on them, I just spray them off with the hose or in some cases use a little 7 on them. All my stuff is usually watered with rain water and lightly fertalized about once a week with miracid.
Any suggestions on whats going on here?

 

[Glaucus]

So the tips of the leaves are brown? If you forget to water, the new shoots will go limp. And you can water then and it will recover 100%, no damage.
But if that never happened, I suspect fertilizer burn. Fertilizing weekly is quite a lot if you use the recommended dose. Is it in an organic mix?

 

[crab apple]

That one is in pretty much inorganic, maybe a little pine bark but not much. The ones in a more organic mix seem to have problems too. I'll be more carefull with the fert and see what happens. Do they need to get really dry between waterings like a Bouganvillia or pine?