Yeah, as Mike said, one consideration is the pot.
Think of the shape and size the rose is supposed to have. Now, picture it "naked." No pot. No soil. The roots should have as much volume as the top. That's a lovely lovely pot, but it's not a good shape for a rose. Look for something you could turn the plant upside down, and put the whole top into. That's what the rose needs. Root room.
Also, that one big round drainage hole isn't ideal. It sounds like the water's going straight through.
The truth is, the Good Lord never intended roses to live in pots. So, if you're going to grow them that way, (and I do, too) you need to adapt a bit.
