Wisteria is a flowering plant that has a climbing habit. It has a very vigorous growth habit and can easily take over an area without annual maintenance pruning. There is a Chinese and a Japanese wisteria. Wisteria is a deciduous plant whose leaves turn golden yellow and leave behind a twisted, interesting woody skeleton. The spring flowers are usually purplish blue but may also be white or dark purple. The proper time to prune is right after the flowers are finished blooming and again in winter.
Japanese wisteria can be identified by its white stems whereas the Chinese variety has a grey stem. Both plants have alternate leaves in groups of smaller leaflets. The plant may grow 25 feet long and is an ornamental species that is prized for its spring flowers. Flowers are borne in racemes that may be 12 to 18 inches in length. In most areas the flowers will begin in May. The Chinese flowers will open before the foliage has sprouted while the Japanese form has both flowers and leaves opening at the same time.
It is important to begin training a young wisteria as soon as possible. The plant has a very rapid growth pattern and will begin to grow up and over the wrong areas if you don't direct it. It is necessary for a wisteria to have a strong trellis or other support. The base of the plant will send up suckers which should be removed to prevent a messy stem. You will have to tie in the vined branches as the little plant grows, until it can send out bigger, more vigorous tendrils which will wrap around supports and hold the plant upright.
Pruning Wisteria in Summer
Wait until the flowers are all spent and then cut back the twirling green ends of the stems. This is the current season's growth and needs to be cut back to just five or six leaves. Remove the spent flower stems unless you want the pods for an ornamental effect. Cut the plant away from any windows, utility boxes or other items it may be covering. In rare cases the plant requires severe pruning, especially when it has been neglected. You may cut a wisteria plant to the ground and it will resume growth.
Pruning Wisteria in Winter
Wisteria will grow almost as big again by fall after its summer pruning. Winter pruning will help encourage flowering. The same stems that you cut in summer are cut again back to two or three buds. January or February is a good time to do this when the plant is dormant. Clear out suckers and tie in any stray growth. Neglected plants should have all the extra weak growth cleaned out of the bushy part so you can open up the framework.