In the wild, trumpet vine (Campsis radicans) climbs to 30 feet or more up trees as it reaches toward the sun. Hardy in U.S. Department of Agriculture plant hardiness zones 4b to 10a, it often smothers small trees when planted in home landscapes and can even rip apart siding if it is planted to close to the house. To prevent damage from its unruly character, train trumpet vine into a neat and tidy tree form. When pruning the plant, dip the cutting blades in rubbing alcohol or a 10 percent bleach solution to sanitize them and prevent the spread of pathogens.
Trumpet vines develop a thick, woody trunk as they age, which allows them to be trained into a small tree. However, young vines need a post to hold them up until the trunk becomes self-supporting. A 4-by-4-inch pressure-treated wooden post 8 feet tall sunk 2 feet deep in concrete is sufficient. Put in the post first, and then plant the vine as close as possible to the base. Only one trunk is needed, so all but the single thickest vine should be removed when planting. Rubber tree ties, found in most garden centers, work well to tie the vine to the post.
Maintaining a Tree Form
As the vine grows, prune off any shoots that emerge from the base or along the main vine selected as the trunk. Shoots that emerge from the trunk above 5 feet from ground level should be allowed to grow into the canopy of the future tree. Cut these back to about 50 percent of their length in early summer and again at the end of summer to keep them short and compact. As the vine matures, continue cutting back all long thin vines to conform to a rounded canopy about 10 feet tall.
Training an Existing Vine
Put in a post next to an existing trumpet vine and cut it back to about 5 feet in height to transform it into a tree. Other then the primary stem, all the growth from below the cut needs to be removed to make a clean single trunk. Vigorous new shoots will grow from the cut, quickly forming the tree canopy. An existing vine probably won't have a straight vertical trunk, meaning it will always rely on the post for support, but it can still take on a lovely tree form.
Solution to a Maintenance Problem
Training a trumpet vine into a small tree prevents it from taking over other plants, but fails to address another problem. This species also sprouts vines from the roots away from the main stem, requiring constant maintenance to prevent a thicket from forming. Planting the vine in a container, and then training it into a tree transforms trumpet vine into a well-behaved plant. Use a large, sturdy container, such as a half wine barrel, and place it on a patio or deck to enjoy the profusion of orange-red flowers in summer.