Trick your spring-flowering trees and shrubs into thinking it’s spring this winter, and into blooming. This is what you do by cutting branches and bringing indoors. The process is called “forcing.”
Trees and shrubs, which bloom in spring, form their flower buds the previous fall. After at least eight weeks of cold outdoors (under 40 degrees F), their branches are capable of blooming if you provide the right conditions. To make sure they receive enough cold, don’t cut branches until after January 1 in a “normal” year or after January 15 in a “mild” year. Branches harvested in late winter often come into bloom indoors sooner than those harvested earlier.
Carefully prune out branches so not to injure the plant or ruin its shape. Use sharp pruners, and cut branches at least 12 inches long. Select branches with a large number of flower buds. These are often on younger branches. Make sure you are looking at flower buds and not leaf buds. The flower buds are usually larger and rounder. If in doubt, cut a few buds open to look for leaf or flower parts inside. Branches force more readily if cut on a sunny afternoon or when temperatures are above freezing.
Bring the cut branches indoors, placing the stem ends immediately in water. If branches are in a bucket, mist them frequently the first few days or enclose in a plastic bag out of direct sun. If possible, submerge the whole stems in water, such as in a bathtub, overnight. This allows buds and stems to quickly absorb water and begin to break dormancy.
The old recommendation was to smash the stem ends with a hammer to improve water uptake by the stems. Sometimes this works, but it may have the opposite effect if stems are mashed too hard. And the mashed ends may make the water more dirty, which will decrease water uptake. The best method is to make a slit or two in the bottom of the stem before placing in the water, such as in a cross or star pattern as viewed from the bottom.
Keep branches in a bucket of water in a cool area (60 to 65 degrees F). Warmer temperatures cause buds to develop too rapidly and not open properly. Change the water every 2 to 3 days to ensure it stays clean.
(Source: Dr. Leonard Perry, Extension Professor, University of Vermont)