Knockouts should do fine in big pots but do better planted in rose bed areas along the deck. No more than one rosebush per pot though as the root systems will otherwise get into a battle for water and nutrients that will cause them to strangle each other. For winter the pots will need to be moved into a garage or shed and insulated or the root systems will likely freeze. You may not have trouble with that were you are though. I am in Colorado and we do need to think of such things here! Be sure the big pots have drainage holes in the bottom as no drainage holes leads to root rot which will kill the rosebushes. If the pots have drainage catching saucers, do not let the water sit in the saucer more than 30 to 45 minutes after a good watering, as this too can cause problems with root rot.
Answered on May 22, 2015
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