For anyone who has travelled around the temperate part of the world in spring, one of the most impressive horticultural sights is often an immense wisteria vine in full radiant glory, with its draping racemes of purple or white flowers covering literally walls, windows and even doors of centuries old buildings. Tracing its branches back to their origin usually reveals a gnarled trunk, somehow growing out of an unlikely space from the paving surrounding the building. I remember sitting under a pergola outside of the Villa Carlotta on Lake Como, Italy and being shaded from the warm September sun by an old wisteria vine with a trunk almost 3 feet across. (I could only imagine what sort of historical events were happening at the time that vine was planted.) While one can easily be overwhelmed with the intoxicating fragrance and overall grandeur of wisteria, it is important to also have a healthy respect for its ability to take over the world if not maintained. A healthy wisteria vine can easily grow 20 to 30 feet a year and if not properly pruned, will soon become a gardener’s nightmare. Here is my sage advice on how to peacefully coexist with wisteria.
Wisteria is native to the Eastern US, Korea, China and Japan. However, most of the popular varieties hail from either Japan or China. To tell the Asian species apart there is one little trick. Chinese plants will twine counter-clockwise and Japanese ones will twine clockwise. (I have to confess that in all the years I have gardened, I have never bothered to see which way my wisteria is twining.)
The majority of wisteria that is sold in local garden centers is grown in California by a wholesale nursery called L.E. Cooke. What makes their wisteria so special is that they graft their varieties onto a seedling rootstock. Doing this allows their plants to come into bloom in the first few seasons rather than taking several years, which is what happens with seedling grown plants. If you have a wisteria that has never bloomed, chances are it is a seedling variety that has yet to reach maturity. Your only option is to embark on a vigorous pruning program, which if you are lucky, will bring it into bloom.
The secret to getting wisteria to bloom is in the pruning. Once it is established, you will need to do a summer pruning followed by a winter pruning. In the summer, which is July and August for us, you will need to cut back all the twiggy growth to within 6 to 12 inches of the main stems. This will keep the vine within bounds and start the process of setting buds for spring. In the winter, you will need to again go in and shorten all the twiggy growth. This time you will need to cut it back to within 3 to 6 inches of the main stems (look for 2 to 3 buds). Those 3 to 6 inch stubs that you have left are where the flowers will develop in spring. This is an aggressive pruning program that may seem extreme if you don’t understand the value of it, but in the end you will have a mass of blooms on a very tidy vine, under which you can pull up a chair, uncork a bottle of Sangiovese and pretend you too are under that pergola on Lake Como. Cin cin!