Answer: Knock Out Roses are grafted onto a rootstock. Any growth coming from below the graft or swelling on the main stem can be considered a sucker. All rose leaves are red when they first emerge so that's not a good indication of whether or not the stem is a sucker or growth from the grafted cultivar. I would trace the stem down to its point of origin. If it is coming from above the graft, leave it alone; if it is coming from below the graft, cut it off. If the growth in question is upright growth from a stem you know is the cultivar, you can simply prune it back. It's not technically a sucker, just part of the Knock Out roses' genetic make up and rambling nature. Knock Out roses are vigorous growers once established. You won't need to prune them all over until next spring but you can certain remove any overly long or errant stems at any time. Since these plants flower on new growth, spring is the best time to prune them down. I take mine down by about a third and they grow well. Hope yours do the same!
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