Your trumpet vine, surprisingly, will do best in soil without too much nutrition. Hold back on the fertilizer and do not amend the soil with overly-rich compost. This plant also needs to have exposure to full sun and may take a few years to mature to the point of blooming. 

Finally, do not prune after late winter or you will take the flower buds for the current season off the plant before it can bloom.

Courtesy of NYBG Plant Information Service