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How do I force branches of spring-flowering plants indoors?
Branches of many spring-blooming shrubs and trees can be forced into bloom indoors several weeks ahead of their normal schedule. For most spring-flowering shrubs and trees this is February and March. Very few plants will force earlier than February because the minimum chilling requirement has not been satisfied. Other plants will not force well until after March. As a rule of thumb, flowers on woody branches can be forced after the buds begin to swell in late winter and early spring. Normally, this is about one or two months ahead of the natural bloom schedule. Branches collected too early result in smaller flowers or shriveled buds that fall off.
The earliest branches to force are pussy willows and witch hazel in January. Followed by forsythia and Cornelian cherry dogwood in early February and Japanese flowering quince, silver bells, flowering cherry, redbud and flowering barberry in late February. Flowering dogwood, magnolia, crabapple, flowering pear, serviceberry and azalea can be collected in early March, but wait until the end of March to force mock-orange, lilac and spirea.
Pick branches you would normally prune anyway. Winter is a great time to prune deciduous trees and shrubs since you can see the entire branch structure without the foliage. Using a sharp pruner and leaving no stubs, take cuttings that have plump flower buds. These can be found on growth of the previous season or old growth of several previous seasons. They are also distinguished from leaf-producing buds by their size. Buds that will produce flowers are typically larger.
After the branches are cut, immerse the cut ends into a container of warm water so that the stems begin to take up water quickly. Some sources recommend that cut branches be totally immersed into lukewarm water for a few hours after cutting, again to prevent a loss of water and keep the buds swollen. Another recommendation is to wrap the branches in wet newspaper until the buds start to open. In any case, store the branches in a dark and cool area (60 to 65 degrees) for 2 days, then slit and scrape the bark off the cut ends up a couple inches. Transfer them to a container of water at room temperature. The water solution should be changed weekly to prevent a buildup of bacteria that can clog up the stems. The stems should also be re-cut each week to promote water uptake. To begin forcing the flowers, move the container to a bright and warmer area. Once the flowers appear which will take between 2 and 4 weeks, the length of the flower show can be increased with the use of a floral preservative mixed with the water.