I wrote this article a few years ago as filler for our bonsai club's newsletter. If any are suffering the same strain of cabin fever I am, I thought perhaps you might like to get outdoors, prune a few surplus branches, and bring them in to enjoy the show. Though I live in the Midwest, many of in other parts of the country have the same or similar plant material that will lend itself to forcing.
Forcing Woody Plants
When the hustle and bustle of the Christmas and New Year holidays are behind us, our thoughts often turn to spring and a longing for the blooms that come with it. While many are already familiar with forcing bulbs and branches of woody plants, its likely a few might not be as familiar with the woody material as they are with bulbs, so I'll try to give a little overview on forcing twigs and branches mixed with some of the science that drives it.
Branches clipped from flowering trees and shrubs can easily be forced into bloom. Trees and shrubs that bloom early in the spring form flower buds the previous fall before dormancy. Successful forcing depends on the type of plant, cultivar, stage of dormancy, and temperatures. Plants begin preparing for dormancy as soon as the length of night becomes longer than day length, around June 21. Changes in growth includes directing energy to newly forming buds and storing energy in roots and cambial tissues. As nights grow longer and temperatures fall, leaves drop and the plant is moved to dormancy. During true dormancy, the tree is in a deep state of rest and protected from cold. The mechanism by which the plant is released from its dormant stage is an accumulation of chill units or roughly - hours of cold temperatures between freezing and 42-44* F. Different plants require different amounts of chilling, but most growing in MI need from 1000 - 1500 chill units. Once an amount of chilling sufficient to release the plant from dormancy has occurred, the plant is capable of initiating growth - usually after several consecutive days of root temperatures near or above 50*. By mid-January, most temperate plants have had sufficient chilling and are technically no longer dormant. This 'after dormancy stage' is often called a period of quiescence, or quiet. It is in this period that woody branches should be cut for forcing. Those that are cut too early will perform weakly with unimpressive displays.
Select the younger, more vigorous branches which will have a larger number of flower buds. Branches high on the p0lant and on the south side (in the Northern Hemisphere) of the plant will have greater energy reserves. Flower buds are usually larger and rounder than leaf buds. If you have trouble telling the difference, cut a few buds open and look for flower parts. Some fruit trees bear flowers on short fruit spurs. Watch for these on apples, pears, and ornamental crab apples. Select branches at least 12 inches long, pruning them flush with the trunk or main branch. By pruning small branches flush, the wound will heal over quickly, with little danger of insect or disease damage. Be sure to use sharp pruning shears or your concave cutters
to minimize damage. Once the branches have been cut, bring them indoors and place the stem ends in water immediately; or better, totally submerge the branches in room-temperature water overnight. A washtub or bathtub works well for this. This soaking allows the branches and buds to begin growing quickly. Following this, place the branches in a bucket of water. Water may need to be changed often to prevent it from becoming foul. Another method, if soaking is not possible, is to place the cut ends of the branches directly into buckets of water and mist the branches frequently the first few days. You might wrap a piece of damp burlap around the branches to help maintain high humidity.
After spraying or soaking, the branches are ready for forcing. The branches should be placed in a relatively cool place (60 to 65 degrees F.) for best results. Higher temperatures will cause the buds to develop more rapidly, but size, color, and quality may be sacrificed. Along with higher temperatures often goes lower humidity, which may cause buds to dry out and fall off. Branches need light for forcing, but not direct sunlight. Heat from direct sun is too intense. If you remember the springtime conditions when these plants bloom naturally, it will be easy to remember the conditions they need.
How can branches, completely isolated from roots, be forced to give up their blooms? As the plant goes from dormancy to quiescence, root activity increases and stored energy (photosynthate, in the form of starches) is moved upward where it adds to the concentration of starch already stored at the base of each bud. As a water supply is introduced, a complicated chemical process begins, metabolizing starch into usable energy. Turgidity increases, cells elongate & the bud opens.
To help the buds open and keep them from drying, mist the branches occasionally during the forcing period. The closer to spring branches are forced, the shorter the time required until bloom. When the flower buds are well developed and starting to show color, remove the branches from the bucket and arrange them. Branches that are removed from the buckets at this stage are less likely to have bruised and broken flowers. Arranging the branches at this stage also allows the enjoyment of watching the flowers open. The branches should be kept in a bright, but not sunny location and will last longer if they can be moved to a cool (40 to 50 degrees F.) location at night.
Some common woody plants you can force:
Red Maple
Alder
Serviceberry
Quince
Hawthorn
Forsythia
Witch Hazel
Beauty Bush
Honeysuckle
Magnolia
Apple
Cherry
Pear
Rhododendron
Pussy and other Willows
Spirea
And many others I cannot think of. Did I say "Have fun"?
AL
