Forcing Bulbs for Winter Bloom
The two easiest flowering bulbs for winter forcing are paperwhite narcissus and amaryllis. Both of these bloom with a modicum of preparation, consisting of placing the bulbs at a shallow depth into potting soil, providing a few weeks of darkness and then bringing the pots out into a brightly lit room. However, spring blooming bulbs such as the common daffodil, hyacinth and tulip can also be forced to bloom in December. These bulbs require the additional step of chilling to induce bloom.
It's best to begin the project with the largest bulbs available on the market. The larger bulbs have greater amounts of stored food and nutrients. This equips them better to grow and bloom in potting mixes, pebbles or even a vase full of water.
Position the bulbs halfway into the growing medium with the root side down. The nose and upper third of the bulb will be exposed. Paperwhites are often placed into a shallow (6" deep or so) dish of pebbles; amaryllis bulbs need a large and sturdy pot filled with soil to support the heavy top growth that will emerge. Spring flowering bulbs should be planted in a growing medium that drains well. The bulbs can be crowded slightly to create a dense area of blooms.
Now it's time to condition the pots. Bulbs require at least four weeks spent in cool, dark conditions to develop roots. Amaryllis and paperwhites are warm-climate plants, so they can be kept in a cellar or garage that stays around 50 degrees Fahrenheit. Spring flowering bulbs need to be chilled. This emulates conditions in nature during which they are exposed to temperatures that hover just above freezing. Depending on the flower type, this period needs to be anywhere from 6 to 10 weeks long. These pots should go into an unheated outbuilding or a root cellar. Moisten the growing medium and put the pots in the dark.
During the dark period, the soil needs to be kept moist in order to encourage root growth. There will also be green shoots beginning to sprout. These are good signs as they indicate the bulbs are viable and likely to produce flowers. By the end of the dark period, the bulbs may well have as much as two or three inches of green showing.
After the dark period has ended, bring the pots into a room in the house that receives several hours of sunlight daily. There is no need to put the pots into direct sunlight; as long as the room is bright, the plants should thrive. The warmth and brightness will stimulate the bulb to send up flower stalks in short order. Paperwhites and amaryllis often flower within three weeks of bringing them into the light. From that point forward, care for these plants as you would any other house plant. Keep the soil evenly moist, feed with a half-strength water soluble fertilizer monthly and trim off the spent blooms.
Sadly, most bulbs can't be forced more than one season. However, many of the spent bulbs can be replanted outdoors. As they go through a normal growing cycle and replenish their food supply from the soil, eventually they can become part of the landscape.