Answer: Trumpet vine (Campsis radicans) blooms on new growth of the season, so avoid pruning in summer as this will remove blooming wood. The best time to prune is late winter to very early spring. Cutting it back quite hard stimulates vigorous new growth and should encourage blooming.
This vine will grow and bloom best in full sun (a minimum of six hours a day including the hour of noon) and average soil. In overly rich soil or if overfertilized with nitrogen it will grow excess foliage at the expense of blooms.
Trumpet vine can take several years to settle in and become rooted and established, before it blooms its best, but after four years I would expect it to be growing and blooming vigorously. You might want to consult with your local professional nursery staff and/or county extension to see if they can help you troubleshoot as well.
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