Harvest in the winter time as with other vines because the sap is down, although summertime harvesting for wisteria is not out of the questions, since most of the time it’s long, straight runners don’t have any leaves. For example, the place I get most of my wisteria for the year is a man’s house who lives close to me - his wisteria runners run under his deck and have none - ZERO - leaves in the summer. The runners grow about 20-40 feet in length and there are hundreds.
Of you’re planning to plant Wisteria around your house or condo, just make sure you’re ready to keep an eye on it during the growing months and train it where you want it to go. Otherwise you will have a beast on your hands - and PLENTY of weaving material.