Woody plants: Let’s look into the science of forcing branches of spring-flowering trees and shrubs to bloom indoors.
As soon as you see buds swelling, forcing can begin. Forsythia and pussywillows can be forced as early as mid- to late February, but it’s best to wait until March for more difficult-to-force plants, such as crabapples, magnolias, spring-blooming witch hazel and redbuds. Forsythia and pussywillows usually take one to three weeks to force, but magnolia branches may take three to five weeks. The closer it is to the plant’s normal outdoor flowering period, the less time it will take to force cut branches indoors.
First, choose branches to force that won’t destroy the natural shape of the shrub or tree and have round, plump flower buds. Narrow, pointed buds are usually leaf buds, though in the case of forsythia, flower buds are usually long ovals. Many flower buds are larger though, and have a more rounded shape than the leaf buds.
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Make clean, slanting cuts at about a 45-degree angle 1-2 feet from the tips of branches with a disinfected sharp hand shears. You can use rubbing alcohol as a disinfectant. If possible, collect branches when temperatures are above 32°F when branches are not frozen. While forcing, keep the branches in a tall container of water in a dimly lighted, cool (60-65°F) location. Mist them a couple of times a day to prevent the buds from drying out, and change the water in the container daily to inhibit bacteria and fungi that could block the vascular system from absorbing water.
When the flower buds begin to open, move the branches into a bright room. Keep the flowering branches out of direct sunlight and in a cool location to prolong the bloom period. Don’t place near a heat register, fireplace or window with direct sun. Branches may last up to seven to 10 days.
— Lisa Johnson, Dane County UW-Extension horticulture educator