In your climate, I am not sure how much summer growth you get. If you water, you will get summer growth. If you don't you may not.

We have some in front of windows and keep them cut back. When they bloom we use the flowers on top for cut flowers. You can avoid pruning if you just bend over the top foliage buds when the flower buds start swelling up to open. This is called pinching some times, but is actually just bending over and breaking off the very top foliage buds so the plants don't grow any taller.

I saw a garden in NJ were the owner did this to his entire planting which was extensive. No plant was over waist high. You could stand anywhere in his yard and see all the plants. It was great.

If you move plants this fall when they are dormant, you are best off if you root prune now by going around the plant with a shovel cutting down in a circle just inside the drip line.

"New roots cannot be produced without energy and if the plant just spent a substantial portion of its supply of readily available energy for new roots as a result of root pruning, and the top has not recovered in its capacity to manufacture energy, the plant will be forced to initiate new roots again following transplanting (with minimal reserves). If the level of soluble energy in the plant and particularly in the roots has not recovered, development of more new roots into the surrounding soil following transplanting may be very slow, and as a result the plant may experience stress to the point of death."

--Carl E. Whitcomb, Establishment and Maintenance of Landscape Plants

Benefit of root pruning at any time questionable.

"...with the multitude of factors involved, both internally in the plant and environmentally, the likelihood of striking the right combination is challenging. At this point root pruning may be one of those techniques that is best to talk about rather than practice."

--Same

Here is what rhododendron experts say:

Ebbett Monroe of Wayside Gardens:
"If you've got to move your azalea or rhododendron, the best course is to give it a root prune in early spring the year before you move the shrub."

Dr. Bob Stamper & Frank Brouse of American Rhododendron Society:
"For large plants, root-prune a few months before digging so that a new root system can develop. With a sharp-edged shovel, simply force the shovel deeply into the soil in a ring around the plant. This will sever the long roots. When finally removing the plant, dig around the plant several inches further out so the newly grown roots will not be cut off. Burlapping the plants will keep the root ball intact but is unnecessary for simple transplanting in your own garden if the ball holds together."

Sandy Feather, Penn State University Extension Service:
"Root pruning is the practice of gradually severing roots around the circumference of the rootball you plan to dig prior to actually digging it. This allows fine feeder roots to fill in the rootball, which helps reduce transplant shock. The fall prior to transplanting is the ideal time to root prune. You can root prune one-third of the circumference, wait a month and root prune the second third, wait another month and root prune the final third. Or you can root prune around the entire circumference by sticking your spade in every other space, so that it looks like a dotted line. Wait a month, then root prune the spaces left the first time around. A spade's depth is sufficiently deep for root pruning"