Hello! I'm generally pretty successful with container plants but I'm having trouble with my first rose bush (double pink Knock Out.) It looked very healthy when I got it about 2 weeks ago, but now the leaves are yellowing and/or drying and falling off (however, there are still a lot of new buds.) It's in a good size container, I used a little bit of rose and bloom food, and I've kept it moist but not soggy. It's on a very sunny open balcony. The only thing I can think of is that I live in New England and the temperature has fluctuated between 50 and 80 degrees every few days. I'm attaching a few photos. Any advice is much appreciated!
It's not dying. You have black spot. You probably brought it home from the store with it. Black spot is a fungal disease that causes the leaves to get those spots, turn yellow, then brown and fall off. There are many fungicide products available from organic ones to chemicals. Find one you like and follow the package directions carefully. For now just remove the damaged leaves and keep them picked up from the ground. It should put out new leaves in a few weeks.
I also think maybe it needs more water and some sun relief during the hottest part of the day. Newly planted roses take time to acclimate to their new surrounding. Pamper it a little and see if that helps. No fertilizer though! It's stressed and fertilizer now would only stress it more. Wait until after it's done blooming and when you see some new leaves starting to grow you can give it some more fertilizer.