Help! I think I'm killing my helleborus
I have three helleborus hybrids I've been growing in pots. I'm not sure exactly what cultivar they are. Anyway, I got them back in March, and they have been thriving until the last few weeks. They were all root bound when I bought them but I cut back the tops and sorted out the roots, and re-potted them. They re-paid me by growing quite a bit and blooming up through May. Its been blistering hot on the east coast the last month so my potted plants have been drying out very quickly. I assumed that was the problem with the helleborus too so have been giving them a good soak whenever they looked droopy. They were also on my front step which faces southwest and gets lots of hot afternoon sun, so I moved them up to the porch which gets more dappled sunlight in case that was the problem. Still seemed droopy/unhappy so I gave all of them a small trowel full of compost. Since then one by one the leaves have dried up, and the stems look dry rotted. It's hard to imagine that I over-watered them because in general I under-water and its been so hot and sunny that all of my potted plants have needed to be watered every few days.
I still have one with a few non-droopy leaves though it looks quite bad. Is there anything I can do? And is it worth keeping the two that look dead to see if anything might come back? I've read that helleborus don't like container culture - is that the problem? Other helleborus preferences like sun and pH sound like they're pretty flexible so it seems unlikely that those were the culprit? I'm very sad to have killed such lovely plants, and for as easygoing as they sound, it's making me doubt the greenness of my thumb!
Thanks in advance for any help and advice!!!