How big are the plants? If they're big you'll need to prune them to reduce the strain on the root system, so losing this year's flowers. I think I'd wait til the soil's a bit warmer anyway. And you'll need to keep them thoroughly watered in dry spells for a year or so til they're established again.

Agree with you Beattie but personally I would wait until Autumn unless the move is unavoidable. Soil still warm but the poor plant won't have to try and get established through the warm/hot summer when evaporation is at its highest.