its technically not a weight issue, but more of a maturity issue. Just like in most things, plants have to reach a level of maturity before they can reproduce, doubly so in perennial plants (as opposed to annuals). If you trimmed every offshoot from a dragonfruit plant and reduced it to a single branch, after a time, usually a growing season, that branch would have developed the chemical production and physical size to create the chemistry necessary to induce flower budding. You wouldn't get much in the way of fruit though, because you would be forcing the plant into an orientation foreign to its natural design. Remember, Mother Nature is a heck of an engineer, and has a way of making things work according to their environment.
Pitahaya is natively a climbing plant, working its way up the landscape to achieve a reasonable size for propagation, which it does in 2 ways:
1. Chemistry changes in the native soil, which correlate with the additional sun and rainfall of the spring and summer seasons, induce flowering, and then fruiting, in order to spread new seeds across the landscape. Sweet edible fruit encourage the process by getting animals to eat the fruits flesh and then deposit the seeds, along with some natural fertilizer, randomly in new places, through hard to digest seed coatings and spotty droppings. BTW, nature's way of adding flowering indicators to the soil is the return of birds to the area, which produce high amounts of phosphorus in their droppings, which gets washed from trees and leaves and into the soil through seasonal rainfall.
2. Branches of plants in low nutrient areas wilt a bit and break off, creating natural cuttings, which also bring new plants, although usually in a more limited radius, but something is better than nothing.
