The best time to prune is Spring. So you are ok. Trim backall the dead parts to about 2 ft tall, to encourage new growth. Having a 'die back' is normal, especially when there was a harsh winter. Don't panic!!! Some even say to prune back to ground level. The new growth, after pruning, is where the blooms will form. But you have to get rid of the die back first. Ok? Tianca