Bud swelling generally begins in the second stage of flowering development, according to the University of Wisconsin Horticulture Department. "Bud swelling" is a term that is used by botanists to describe the phases following bud inactivity and precedes bud break in the developmental morphology of flowering trees and plants.
Buds are embryonic flowers or fruits. According to Cornell University's Department of Agriculture and Life Science, all buds follow a systematic developmental process, but differ in size, stem growth, number of phases and whether the plant produces flowers and seed, or flowers and fruit, which contains the plant's seed.
Modern horticulturists and plant biologists have developed terminology for explaining the developmental stages relevant to specific flowering plants and trees. The cranberry, for instance, has about nine developmental phases. The inactive or dormant bud, the tight bud, the swelling bud, "cabbagehead," "bud break," "bud elongation," "roughneck," "hook" and "bloom." The cabbagehead is the pinnacle phase of bud swelling prior to bud break. The burgeoning cranberry bud resembles a head of cabbage at this stage. Other fruits have specific terms as well -- also named for the changing appearance of the buds -- apple buds for instance have stages that include "silver tip," "green tip" and "tight cluster," while plum, pear and peach bud-swelling stages include "swollen bud" and "bud burst."
The bud-swelling phase marks the point where the plant moves into an active growth phase from its dormant period. According to horticulturist Judith Adams, writing for Canada's "Garden Making" magazine, it is unwise to force a plant out of dormancy. She advises gardeners to utilize plant stimulants such as bone meal, transplant supplements and supplements with vitamin B1 only when the plant begins to show it has begun a growth phase. Generally warmer days and longer days produce natural plant hormones and small bud swelling is visible on woody stems that signal the growth cycle has started.
Shrub roses and other perennials should be pruned during the bud-swelling phase, before leafing out. Pruning during this phase is healthy for the shrub and encourages more flowering. It is a good time to remove suckers and dead branches from the shrub, according to "Pruning A Shrub Rose" in the online edition of "Horticulture." Pruning other shrubs and trees depends on whether the plant blooms on new or old wood. Plants that, like shrub roses, bloom on the current season's growth, such as butterfly bush or crape myrtle, can be pruned at this time. Plants that flower on last year's growth, like oakleaf hydrangea or lilac, should not be pruned until just after blooming.