Q. Could you provide some advice on forcing early blooms indoors for flowering trees and shrubs? I tried this past December and had very little success. -- Michelle F., Westfield
A. The process of encouraging early flowering is appropriately called forcing. We can force plants to flower earlier than normal by modifying temperature and light conditions after plants have completed a necessary period of dormancy.
It is important to force spring-flowering trees and shrubs only after the plant experiences dormancy during the cold weather. It is okay to force some plants, such as pussywillow and forsythia, in mid- to late January. For other plants, such as redbud, magnolia and crab apples, you may have to wait until mid- to late February and beyond.
There are methods to overcome this dormancy requirement, but I will adhere to the basics for this article. The dormancy dates will vary each year, depending on outdoor temperatures and other environmental factors.
Selection and timing
Flowering trees and shrubs that will provide excellent indoor flowers when forced include forsythia, pussywillow, magnolia, redbud and crab apple and other fruit trees. Even red maples will provide small reddish flowers for a burst of color.
Mid-January through February: Forsythia's cuttings produce yellow flowers in one week to three weeks; Cornelian cherry produces yellow flowers in about two weeks; poplars produce long-lasting, drooping flowers called "catkins" in three weeks; willows produce a similar type of catkin in about two weeks and witch hazel produces beautiful yellow flowers in as little as one week.
Mid-February to early March: Red maples produce pink to red flowers in two weeks, birch produces catkins in two weeks to three weeks, cherries produce white to pink flowers in two weeks to four weeks, rhododendrons and azaleas produce flowers in a wide range of colors, depending on the variety, in four weeks to six weeks (wait until late February to collect these) and pussy willows produce fuzzy flowers in two weeks.
March: Hawthorns produce white and red to pink flowers in four weeks to six weeks; apples and crab apples produce white, pink and red flowers in three weeks to four weeks; lilacs produce flowers in an array of colors, depending on variety, in four weeks to six weeks, and spirea produces white to pink flowers in about four weeks.
Tips for forcing and care
Select branches that are 12 inches to 14 inches long and contain many large flower buds. Remember that flower buds on most plants are larger and often roundish compared to leaf buds. For plants such as forsythia, shoots at the top will often contain the most flower buds that are closely spaced for a more colorful display. Collect branches on a warmer winter day.
Remove side branches and buds that will be submerged in water to prevent rot. Cut the branches at a 45 degree angle or leave a long slant and place in a tall vase with lukewarm water. Change the water in the vase daily to prevent foul odors and reduce the potential for rot.
Place branches and vase in low light and cool temperatures (60 degrees to 65 degrees Fahrenheit to start). Mist plants two to three times per day to prevent buds from desiccating. Once flowers begin to emerge, move plants to a brighter room, but keep them out of direct sunlight. Keep flowers in a cooler location, away from direct heat sources, to prolong the bloom.
Some plants such as pussy willow and forsythia may bloom in one week to three weeks, whereas other plants such as magnolia and crab apple may take three weeks to five weeks. As the season continues, it will take less time to force indoor blooms.
Avoid excess pruning
Remove only a few select branches of the tree or shrub, being careful to not disturb the overall shape of the plant. Excessive removal of limbs and buds will limit spring flowering and may damage plants. Base your pruning on the size and maturity of the plant and follow proper pruning procedures.