It's possible that an excess amount of fertilizer/wrong type of fertilizer did damage the root system. In any case, mid-July is too late for fertilizing. A late flush of soft growth will not have enough time to harden off before winter. Fertilizing in the first year after planting - or any other time - without a soil test indicating a need for it is never a good idea. The weather conditions you describe are ideal for phytophthora infections, but those that effect the roots would be nearly impossible to diagnose from looking at a leaf. Poor drainage is probably the number one cause of root rot problems, so anything that can be done to improve it would be worthwhile. Do cut back to healthy green tissue and be patient. The presence of buds is a good sign and it's highly likely that the rhododendrons will recover.

I'm sorry but it doesn't sound promising :-( Not sure how large of containers we are talking about but warm(hot) weather and exposure to late afternoon sun can dry them out very rapidly. They may need daily watering. I'd recommend planting them in the ground ASAP if that works for you. Helleborus x hybridus is less adaptable to container culture than some of the other hybrids but any hellebore would prefer a permament, inground planting location. xhybridus is the least sun tolerant as well - morning sun and afternoon shade is preferred, not the other way around.

Hi Bernard, I hope I don't repeat something because I only got about halfway through this thread before I got sick of reading and decided to go ahead and post. #1. I don't know where the idea come from that calloused roots are good. Callouses can't absorb water. It's dry scar tissue that keeps in/out moisture, thereby protecting broken stems and so on. When a plant's roots are partially exposed by wildlife digging, etc., the exposed portion callouses to keep the plant from dehydrating, but that calloused portion will never absorb water again. We don't want roots to callous (except maybe Bonsai growers who like to expose some roots over a rock or something). Putting a root system into dry mix is never good for it. I challenge anyone to prove how dehydrating or callousing a root system can possibly be good for it. The previous poster who said the dry mix will dehydrate the plant is correct. Always use damp mix for re-potting a healthy root system. If the roots are dead, it might be a different story. #2. As you've already learned, it's easy to under-water gritty mix. Since it's pretty close to impossible to over-water grit, I'm with the posters who say to soak it deeply and often. If you're paranoid, soak it daily, or even twice daily, but then give the pot a quick, little down-up motion to dislodge any perched water. That way it'll always be just barely moist. If it were mine, and planted in grit, I'd just water every day or two until the roots are well-established. As one who has killed off whole, healthy root systems by under-watering grit (once weekly), I feel confident in telling you that you're extremely unlikely to drown a plant in grit. I'm watering my succulents daily right now, and some are STILL too dry. BTW, Danny, I think mentioned he prefers soil for jades. I don't disagree with him. The one I have in soil has grown much better than the ones I have in grit. Furthermore, the Aeonium I had in a 1:1 soil:pumice mix has a huge, beautiful, healthy root system. The big one in grit has puny roots. These aren't experiments with standardized variables, so something else might be going on, but for now, I'm also not certain that grit is always a better medium.

Be sure you cut away every bit of soft tissue. If you save partial pads, cut into healthy tissue to be sure you've cut away all mush. Bacteria grow rapidly in the damaged tissue and can sometimes spread to healthy tissue when a plant is stressed or dormant, so be sure to get rid of that stuff. Opuntia species are fantastically resilient and easy to propagate. I have seen Opuntia pads root from between blotter papers in a plant press left over the holidays in a cold, dark botany lab. You needn't keep them damp. They have adequate moisture in the pads to feed new root growth, and they can't absorb moisture through the "skin" anyway, so my feeling is that adding moisture will only increase the danger of rot. Personally, I think it will root just fine if you lay it on top of dry soil. Just be sure the damaged portion scars before you let it get at all damp. Some Opuntia species are very cold tolerant. Others aren't. There is one species that grows wild around Boulder Colorado- Opuntia compacta maybe. That isn't your species, but it's easy to see why you thought it might survive such intense cold. I hope you can salvage some. It looks like one of the more attractive Opuntia.