Is there a climbing plant that can be used in conjuntion on a trellis with wisteria that has an alternate bloom time?
Hard to find one as vigorous that could compete with the Wisteria. Trumpet vine (Campsis) flowers during the summer with orange or yellow flowers (depending on variety). How big is your trellis? Wisteria is not a vine for small places. Simon
One of the more vigorous clematis might manage to poke it's head (or heads) through the wisteria - try the montana group. You should still endeavour to keep on top of the pruning. An underpruned wisteria is a runaway wisteria. In anycase, wisterias flowers best with regular pruning, keeping the growth of new, adventurous vines in check.
I have armandi snowdrift clematis with my wisteria and it's great! The snowdrift flowers feb mar april white flowers very very fragrant. Also it is evergreen- so when the wisteria loses all its leaves, you still get the green waxy leaves of the snowdrift for color and privacy. Goodluck