re: How should I apply fertilizer to these Roses?

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I'm trying to discourage growth at this point, so I'm gong to try a warm season cutback to put them in check.

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Just read this:
Overall, Knock Outs can be taken back by about 1/3 of their height, keeping in mind overall finished shape. Knock Outs tend to grow in phases (bloom - rest - bloom). If a mid-season trim is in order, it is best done following a blooming period while in the resting phase. Deadheading will also help to stimulate new bloom clusters and overall growth. Knock Outs tend to produce a lot of rose hips that inhibit flowering (triggering dormancy), so trimming these off will keep your Knock Out blooming.

I think I’ll try the mid season prune and then get them back in shape next February. But for now, we don’t mind the lush look and I think they’ll still flower pretty well.
Last year was spectacular.