Hi Jeanne.
Cutting back hardy hibiscus is not responsible for them not blooming. Most likely the cause was lack of food and as you mentioned, the crazy weather we had. You need to feed these guys to encourage blooming. The best is a hibiscus family, Malvaceae, specific food but any 1 tbs per gallon does just fine .. but make it a little richer - about 1.5 tbs per gallon. But only for plants in the ground. They also do best with a minimum of 6 hours of full sun.
I find the best time to cut them back is after the 2nd killing frost. That way they won't be putting out new growth.
