Neil,
When will your first frost date be? Ordinarily, you wouldn't fertilize roses plants now because they should start going dormant in a month or so. Meaning, their energies should be concentrated in keeping their roots healthy. Fertilzing would encourage more foliage and flower growth and this could deplete the plants energies when it should start to go dormant (in my area that's in a month or two).

Fertilizing is done best in spring to early summer. In my case, I use composted manure and bonemeal. That does the trick.

Thanks , we probably should expect frost by mid Sept. or sooner. I'll save the fertilizer for spring..
Neil

NO!NO!NO! new growth will not develope in time to survive freeze.
Bill A very long time gardener.