The only things that will stop a trumpet vine from flowering are not enough sun (they would prefer at least 7 hours of direct sun and more is even better) or a lack of phosphorus.  Avoid high nitrogen foods (those with a high 1st number (like 30-10-10) and feed it with a plant food with high middle and last numbers.  I’d suggest Espoma Flower-Tone (3-4-5) in spring as soon as the ground warms up a bit.