Ask Mr. Smarty Plants

There are numerous cultivars of the Trumpet vine which are derived from the native species Campsis radicans (trumpet creeper). The main reason for planting Trumpet vine is for the showy, trumpet-shaped flowers, so when the plant doesn't produce, it can be disappointing.

Its hard to know why plants won't flower, but let's look at three possibilities. From the Floridata write up of Trumpet vine, there are two pieces of information that may be pertinent. The first is that the plant can grow in shade and full sun, but flowers best in full sun. Secondly, the plant is native to the southeastern and Gulf  regions of the U.S., but can survive in USDA Hardiness zones 6-9. Lowell appears to be in zone 4, so the plant may not be happy enough to flower in its current location.

Another factor that affects flowering in plants is the amount of fertilizer that they receive, particularly the balance between nitrogen and phosphorus. When the nitrogen:phosphorous ratio is too high (more nitrogen than phosphorous) many plants won't flower. If your plant is in a location where it receives regular lawn fertilizer which is higher in nitrogen than phosphorous, this may be a part of the problem. This article from Gardening-Advisor has some good advice about fertilizers and fertilizing.

For help closer to home, you might contact the folks at the UMass Extension Office in Waltham, MA.

I'm including the Davesgarden website to make you aware of problems other people have with Trumpet vine besides lack of flowering (scroll down to the"gardeners' notes").

Campsis radicans