How to PRUNE Wisteria… If you grow wisteria you might be familiar with the pruning, and understanding it needs to be pruned twice a year BUT… This summer hair cut is only needed IF you are happy with the size and shape of your wisteria. If you are wanting to spread it, make it bigger, cover more fence, twist it around a pergola then DONT SNIP! You want to be tying in those fresh whippy shoots. They are really soft and so easy to work with. You can tie with string and this will hold them in place