The term forcing refers to inducing a plant to produce its shoot, leaf, and flower ahead of its natural schedule and out of its natural environment.
Many spring-blooming bulbs can be forced to flower in late winter and early spring. Tulips, narcissus (daffodils), hyacinths, crocus, and grape hyacinths, are the most common choices. Catalogs and garden center displays often indicate which cultivars and types of bulbs are more suitable for forcing. Choose only top size bulbs for the best blooms.
Almost any container can be used for forcing bulbs. The best containers are clay or plastic with good drainage holes. Hyacinths can also be forced in specially designed vases.
The best soil mix contains equal parts of soil, sphagnum moss, and perlite or vermiculite. Commercial “soil-less” potting mixes can also be used. Do not use ordinary garden soil or potting mixes labeled “potting soil”. These soils hold too much moisture and may cause water-related disease problems.
Fill three-quarters of the container with soil mix and plant the bulbs closely together. Don’t press the bulbs into the soil. Place flat sided bulbs next to the edge of the container as the largest leaf will always emerge and grow on that side. Once the bulbs are arranged in the container, place additional soil mix around them leaving the “noses” of the bulbs exposed. The bulbs should then be watered thoroughly.
All spring-blooming bulbs, with the exception of paperwhite narcissus and amaryllis, must have a cold period of at least three months to initiate bloom at an ideal temperature of 35 – 48 degrees F. The easiest way is to store the pots in an unheated garage or cellar. Bulbs can also be stored in the refrigerator’s vegetable section and should be covered with plastic bags that have a few breathing holes punched in them. Check the bulbs frequently to make sure the soil remains moist and does not dry out.
After the bulbs have been chilled, bring the pots inside, check for visible roots at the drainage holes, and water them thoroughly. Place pots in a cool, sunny location (50-60 degrees F) until active growth is visible. Once active growth begins, move the pots to a warmer location avoiding direct sunlight. Move blooming bulbs to a cooler location at night to prolong the life of the flowers. It generally takes 2-4 weeks before the plants actually bloom although it will also depend on the environmental factors in the home.
Amaryllis and paperwhites can be planted and will bloom without special treatment. Amaryllis should be potted in a light rich soil in a pot that is only 1-2 inches larger in diameter that the bulb. The upper half of the bulb should be exposed above the soil. Water thoroughly and allow the soil to become dry between waterings. Place the plant in a warm, sunny spot until the flower buds show color, then remove it from direct sunlight.
Paperwhites can be easily forced in a shallow container of water using pebbles for support. The easiest after-bloom care is discarding the spent bulbs as they are not likely to flower again satisfactorily.
By Carol Matheson, Penn State Master Gardener, 2011 September/October Newsline