Wisteria that fail to bloom most often require more sunlight than they currently receive, according to Jane C. Martin of the Ohio State University Extension. For best results, select a place in the garden where wisteria plants receive a minimum of six hours of sunlight per day. Neutral to slightly acidic soils work best, especially those with a pH between 6.0 and 7.0.
Notorious for their potentially invasive quality, wisteria plants require pruning and training to maintain size and scale. Unfortunately, improper pruning may compromise a wisteria plant's blooming quality. Winter is the best season for pruning because gardeners have an easier time with the vines cleared of blooms. Be careful not to remove too many of the flowering nodes, warns Gerald Klingaman of the University of Arkansas Department of Agriculture. For neglected and overgrown vines, prune back crowded branches, remove suckers, leaving one strong central leader from each framework branch. After this drastic pruning, it may take two or three years for plants to bloom.
For some types of wisteria, plants must mature before they produce blooms. Growing wisteria from seed is not recommended, as some Asian varieties require more than 15 years to begin to produce flowers, according to B. Rosie Lerner of Purdue University. On average, seed-grown wisteria takes five to seven years to begin producing flowers. Plants grown from cuttings produce flowers within two to three years. Klingaman warns that young plants require an effective support system. Well-supported juvenile plants mature properly, developing healthier growth habits.
In some cases, exposure to harsh winter temperatures contributes to a wisteria plant's failure to bloom. A late-spring freeze causes damage to young flower buds. Provide protection for wisteria in areas where below-freezing weather commonly occurs in the mid- to late spring.
Tips to Encourage Blooming
According to Martin, gardeners may encourage wisteria to bloom with a few simple tips and tricks. Treat wisteria vines with a super-phosphate fertilizer, typically marked 0-20-0 on the container. Apply in the early spring for best results. For established vines that do not bloom, prune new growth back in the late spring. In the early summer, prune wisteria roots.