I'm in Tampa. I've grown them in the ground and in pots...I prefer growing them in pots. I've heard it said that they need to be in at least 10 gallon pots but I've grown them in much smaller pots. I've used those low & wide pots (squat pots) and I'd say those are only about 3 gallons. The trick with the smaller pot is getting enough water on them in the heat of the summer. Right now I am growing them in 7 gallon pots.

I like that I am able to control the conditions of roses better in pots. We like to use Fafard 3B potting mix which I'm sure is available some where in your area.

A trick that an EXCELLENT rose grower told me was that after a couple of years in a pot they need to be root pruned. Remove them from the pot and prune the roots as well as the top. At this time it is also possible to divide the plant. The roses I am growing now are young...none over 1.5 years old so I haven't tried this method of rejuvenating them.