Answer: The most common reasons for this vine not to bloom include lack of establishment, too much shade, too much fertilizer, and/or pruning at the wrong time. Trumpet vine or Campsis radicans can take a year or two to settle in and become rooted and established before it begins blooming its best.
It does best in a full sun location, with direct sun all day or for a minimum of six hours including the hour of noon. In too much shade it will be sparse and leggy with fewer blooms.
It needs only average fertility, so I would not recommend extra fertilizing with a liquid soluble fertilizer. Oversupplying it with nitrogen will encourage vegetative growth at the expense of blooms. A spring top dressing with a good quality compost along with possibly a general purpose slow release or granular fertilizer such as 10-10-10 (or similar proportions) per the label directions should be adequate. If it is growing adjacent to a lawn that is regularly fertilized you may not need to fertilize the vine separately.
Lastly, this is a very large vine. If you need to prune to control size or want to encourage denser growth or more blooms, trim it back as hard as desired in late winter to early spring. This will encourage vigorous new growth. It blooms on new growth of the season, so do not prune in summer. If you prune in summer you remove the flowering wood and/or flower buds. I hope this helps.
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