Dragonfruit grows on the tropical vining pitaya cactus. A deep red, the fruit is more than 4 inches long. The cactus may reach a height of 20 feet if supported properly. Trellising is a must for this cactus; otherwise, it sprawls over the entire garden, and the dragonfruit becomes prone to disease and rot. A standard lattice trellis is not strong enough to support the weight of the cactus. You need to build a sturdy trellis tree for each plant.
Dig a 2-foot deep hole with a post-hole digger. If building more than one trellis, space the holes 4 to 10 feet apart so plants have room for top spread on each trellis.
Set a 6-foot-tall, 2-by-4-foot wooden post 2 feet deep in each hole. Firm the soil around the post so it does not shift or buckle under the weight of the plants.
Cut a 4-foot-length of 2-by-4 wood. Set it on top of the wooden post to form a T-shape. This two-by-four is the trellis crossbar.
Drill the appropriate size hole for your bolts through the cross bar and into the post. If possible, drill two holes side by side to allow double bolting. Screw the bolts in tightly to hold the cross bar to the post.
Plant your dragonfruit cactus at the base of the trellis. Guide the cactus up the post, tying loosely in place as necessary with cloth plant ties. Once tall enough, allow the cactus to spill over the crossbar so it resembles a tree.