Answer: Weigela may fail to bloom due to insufficient light, winter damage, or incorrect pruning. This shrub needs full sun all day long to bloom its best, or at a minimum for half the day including the noontime hour. It blooms on old wood that grew the year before. For this reason any pruning should be done right after it blooms and ideally would consist of only some light thinning, meaning removing a few of the oldest branches each year. If winter kills back the branches, and you are thus forced to trim them back, this will limit flowering. You might try a windbreak to help with winter damage. A well drained planting site is also helpful in reducing winter damage.
Wisteria grown from seed can take about eight years to bloom, but 20 years is not unheard of. So if your plant was seed grown then it may just be a matter of time. Otherwise, it might be related to your pruning or to overfertilizing. Oscillating temperatures in the spring can also damage flower buds before they open. The following information should help you troubleshoot the wisteria and its care in great detail.
I hope this helps!
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