The mid-winter landscape is still fast asleep, the scents and colours of spring flowers months away. But an armful of bare branches and some simple conditioning methods can fill the house with bursting blossoms to tide us over until spring catches up. The trick is to understand how shrubs produce flowers, then mimic the natural process indoors to force them into bloom.
Many flowering shrubs such as forsythia, quince and lilac set their buds on one-year-old wood that produces flowers in early spring. After the spring blossoming period, the shrubs produce new wood and, by late summer, have set flower buds on it for the following year. As summer turns to autumn and air temperatures begin to drop, the buds enter a rest phase, which reaches its apex in early winter when they're entirely dormant. They must be thoroughly chilled for a specific period of time (which varies by species) in order to bloom in spring. For example, branches from fruit trees require an outdoor chilling temperature consistently below 7°C. Apples require a longer chilling time than peaches, peaches more chilling hours than almonds.
It isn't necessary to know the exact number of chilling hours for individual shrubs: forsythia, for instance, requires a relatively short chilling period and branches can be cut in late January, while magnolia needs more time and should be cut in early March. (See our chart on last page for more species and when to cut them.)
In general, cut branches four to six weeks before they would normally bloom outdoors, selecting wood on which immature buds are clearly visible—the closer buds are to their natural blooming time outdoors, the faster they will bloom indoors. Try to select shrubs that have extra twig and cane growth, and would therefore benefit from shaping. When choosing a branch, look for wood 2.5 centimetres in diameter or less. It's possible to cut larger wood using a small pruning saw, but handling large pieces and keeping them hydrated is more difficult. Using pruning secateurs, make a slanted cut in the branch just above a bud—slim, elongated ones contain foliage, while larger, rounded buds form flowers.
If branches are cut on a day when the temperature is below freezing, bring them inside and try to submerge them entirely in cold water (in a deep sink or bathtub) for two hours so they can warm up gradually while remaining totally hydrated. This will also prevent buds from cracking in the warm indoor air. If the outdoor temperature is above freezing, make a slit in the bottom of each branch, using pruners to slice upward about 2.5 centimetres. This allows a greater area for water uptake. Don't crush the tips with a hammer (a practice suggested by some sources), as this damages plant tissue and encourages bacterial infection.