November 2001 - Forcing Bulbs

Provided by the Western Massachusetts Master Gardener Association

A pot of daffodils or tulips blooming indoors in the middle of winter can cheer anyone suffering from cabin fever. You can always buy flowers prepared by the florist, but it’s more fun to do it yourself. As long as you can provide the proper temperature conditions, it's easy to force bulbs.

“Forcing" may sound cruel, but it is simply speeding up the natu­ral process by tricking the bulbs into thinking winter is over early. It doesn't harm the bulbs, which can be planted in the cutting garden to bloom again in subsequent years.

The critical factor for success is providing the proper tempera­ture. The potted bulbs cannot be allowed to freeze; that is, they must be above 32 degrees. They also must be kept below 50 degrees or else they will attempt to flower prematurely and will "blast,” or fail to bloom.

How can you provide the preferred temperature range of 38 to 50 degrees? An extra refrigerator is ideal, but most people don't have that luxury and don't want their family refrigerator crowded with messy pots of soil.

An alternative is a cold frame. If you use this method, place the pots on a chicken wire grid over sand to prevent them from freezing into the ground.  A few mousetraps will deter rodents. Fill the frame with leaves after the ground freezes. The cold frame should be near the house to facilitate retrieval of the pots in snowy winters.

Another method is to place the pots in heavy-duty plastic lawn or leaf bags stuffed with leaves, and keep the bags in an unheated basement, garage, bulkhead or barn. For added insulation put the bags in clean trash cans or cardboard appliance boxes also filled with leaves.

Now for the easy part: planting the bulbs. Use sterile pots and sterile soil. Squat bulb pans or azalea pots are recommended but regular-shaped pots can also be used. Half fill the pots with moist soil, arrange the bulbs in the pots and cover them with soil. Place the flat side of tulips toward the outside since this is where the first leaf will develop. It's okay if the tips of the bulbs remain uncov­ered. Water well, drain and then put the potted bulbs to "sleep."

Sleeping is a misnomer, however, for the bulbs will develop roots in cold storage and eventually the tops will start to sprout. It's time to bring them inside for "forcing" when the green shoots are about an inch or two inches high.

Daffodils, tulips and hyacinths require 10 to 12 weeks of cold storage. The "little" bulbs--crocus, snowdrops, or scilla only need 6 to 8 weeks.

When you bring the pots inside, acclimate the plants slowly to light and warmth. Keep them out of bright sunshine for the first few days until the tops are truly green, Then place in a sunny window and keep watered, but not soggy wet, while the flowers develop. Cool temperatures are essential to proper forcing.  Don't keep the pots near the woodstove or other heat source.

The bulbs will bloom for a week to 10 days. Keep the leaves growing and plant them outside in late April or early May. They won't bloom again in 2002 but should produce flowers in future years.

Provided by the Western Massachusetts Master Gardener Association