"Forcing" is the term used to describe the process that stimulates bulbs to bloom out of season. Among the most commonly forced bulb flowers are muscari, tulips, daffodils, amaryllis, paper whites and hyacinths.
Spring flowering hardy bulbs require a rooting period of about 12 to 15 weeks at temperatures between 41-48°F in order to produce a good root system. Store bulbs in a location where this temperature can be maintained throughout the entire rooting period. Non-hardy bulbs such as amaryllis and paper white narcissus do not require this type of rooting period.
Bare bulbs can be stored for several weeks in the refrigerator prior to potting without damage if they are packed properly, in an onion bag or paper bag with holes in it to provide airflow. However, they will still require the rooting period after they have been potted, as storing them was just to keep them from rotting.
Some locations to consider when rooting the bulbs include a working refrigerator, putting the bulbs into the vegetable crisper drawer. Be sure they are no where near apples which gives off ethylene gas. Another thought would be to use an unheated basement or root cellar, or even an unheated garage as long as the temperature does not go below freezing.
Some bulbs like hyacinths can be forced in special forcing vases. These vases have a narrow neck that allow for the bulb to sit above the water, with just the roots in the water.
Another popular vessel for forcing bulbs is using a decorative or plain pot. Use clean pots with drainage holes. Try to allow for 2 inches of plain potting soil below the bulb and select a pot large enough to allow the top of the bulb to be even with the rim when placed on the soil.
Place soil in the pot, then carefully place bulbs into position. Add enough soil to fill the pot, firming the soil gently around the bulbs. too vigorous handling can bruise the bulbs so be gentle. Water well.
It may be helpful to label each pot with the name of the variety, planting date, and the date to bring it out of storage for forcing. This is especially helpful if you are targeting a certain date for gifting, such as Christmas or Valentine’s Day.
Bulbs will flower in 3-4 weeks after they have been brought into warmer temperatures. From time of planting to flowering, allow a period of 15 weeks, determined by needing 12 weeks for rooting, and 3 additional weeks in warmer temperatures to flower. Here is a guide but remember that plants can vary.
To flower in January, plant in September or very early October
To flower in February, plant early- to mid-October
To flower later, plant in late October or early November
The actual forcing begins when you remove the bulbs from the cool environment into warmth and light, which triggers the growth of leaves and flowers. Sunshine and warm, not hot , temperature are the most important factors in promoting successful flowering. Transfer the pots to a place indoors with indirect sunlight and temperatures about 60°F for a week or two.
When the shoots are 4-6 inches tall, move the pots to a bright, sunny window to stimulate blooming. A temperature of about 68°F and bright sunlight will produce the best results. When the buds take on color, return the plants to indirect sunlight to make the blossoms last. Keep the soil moist at all times.
After blooming, hardy bulbs such as hyacinths and tulips cannot be forced again, however, they can be planted outdoors where they may re bloom within a year or two.