In northern climates forcing bulbs gives you the pleasure of colorful flowers in the dark of winter, plus the satisfaction of creating this indoor garden of delight yourself. Forcing can be a little tricky. It may take some trial and error, but once you get the hang of it you can have fresh flowers every winter. Best of all, they’ll be as pretty as any of those expensive floral arrangements from delivery services or your local florist or grocery store that sells flowers, but you’ll have grown them yourself.
When you force bulbs you are getting them to grow and flower at a time of year that is not their normal flowering time. You artificially give them the conditions they need in order to prepare for flowering. Popular garden bulbs like tulips and daffodils, for example, need to go through a cold winter; to force them you keep them cold for the required amount of time. Other bulbs have specific light requirements.
Bulbs for forcing fall into two general types: hardy garden bulbs like grape hyacinths, early tulips, crocus, daffodils, etc. and tender bulbs such as amaryllis and paper white narcissus. The two types require different treatment; this article focuses on forcing hardy bulbs.
Always use high, quality top-size bulbs and handle the bulbs with care. Don’t expose them to temperatures above 65 degrees. The forcing process involves three steps: Planting, cold treatment, and actual forcing.
Potting the Bulbs
Plant the bulbs close together in clean clay or plastic pots using well-drained potting soil. Bulb pans, which are squatter than regular pots, are ideal but not essential. Fill a pot part way, place the bulbs on the soil without pressing down on them, then cover the bulbs, leaving their “noses” exposed. Arrange the bulbs so the flat sides are next to the rim of the pot. Leave one-quarter inch of space above the level of the soil for watering. Don’t mix different types of bulbs in one pot because different bulbs flower at different times. Water the bulbs right after you plant them and keep the soil moist.
Keeping Bulbs Cold
The potted bulbs need to spend about three months in the cold, so you’ll need to pot them in the fall for winter blooming. To keep them at 35 to 48 degrees you can put them in an unheated attic, room, or cellar or the vegetable section of your refrigerator. If you put them in the refrigerator, cover the pots with plastic bags with a few breathing holes. You can also leave them in an outdoor cold frame, but you’ll need to mulch them heavily to keep them from freezing.
Forcing the Bulbs to Bloom
After you take the pots in from the cold, start them out in a cool area (50-60 degrees) for about a week until shoots and leaves show. Then, move them to normal room temperature, avoiding direct sunlight. They will bloom in three to four weeks. The closer to spring, the quicker they will bloom. Bring out pots weekly for a continuous display. You can prolong the flowering by moving the pots back into the cool at night once they start to bloom.
Sadly, once forced most garden bulbs will not bloom again, either indoors or out. Thank them for their service and send them to the compost pile after flowering.
Want to learn more about winter gardening and forcing bulbs?
To find out more about forcing bulbs, including how to grow paper white narcissus and amaryllis, check out these websites:
Forcing Bulbs for Indoor Beauty in Winter by University of Minnesota Extension.
University of Rhode Island Landscape Horticulture Program factsheet on forcing bulbs.
Forcing Bulbs for Indoor Bloom by Purdue University Cooperative Extension Service.
Lynne Lamstein gardens in Maine and Florida and is currently working on a sustainable landscape. She has a degree in ornamental horticulture from Temple University.