We cross-posted here, but I agree and disagree with your new comment. It's true that carelessly hosing off the nursery medium could break the feeder roots, but I shake it off in the case of the Trader Joe's medium for mini-roses, and I'll probably soak it off any new potted roses I plant if the nursery has used a bark-based medium. I don't wash the soil off if there's any soil, but some nursery media don't seem to contain any soil. In any case, there's no need to use a strong hose spray to remove anything.
I can't say anything about your fertilizing comment. I've never used fertilizer on anything in my garden, aside from Osmocote pellets in pots of annuals. Daily watering is almost essential here in summer and I can't imagine fertilizing every time I water. For one thing, I'd soon go broke.
