Forcing bulbs is one method of starting spring a little early indoors. Forcing bulbs to bloom when you want them to, rather than when they normally do, is possible because of the growth habits of most spring-blooming bulbs.

Bulbs have a general growth cycle. In late summer, most are dormant with little if any active root growth and no shoot growth. As soil temperatures cool, the bulbs begin root growth. This growth continues until cold temperatures stop or reduce to a minimum root growth. As temperatures begin to rise in spring, shoot growth begins, with flowering following fairly rapidly.

After bloom, foliage continues photosynthesis and replenishes food stores in the bulbs. Offsets are being produced, and formation of next year’s flower buds is occurring. As foliage begins to die back, the bulb returns to a dormant state, and the cycle is ready to begin again. Forcing is simply manipulating this cycle.

Choosing bulbs—Most spring-blooming bulbs can be forced into bloom. The most common choices are hyacinths, tulips, narcissus, grape hyacinths, and crocuses. Catalogs and garden center displays often indicate which cultivars and types of bulbs are more suitable for forcing. Choose only top size bulbs.

Containers—Almost any container can be used for forcing bulbs. Specially designed vases for forcing individual hyacinth bulbs are available. Paperwhite narcissus can be easily forced in a shallow container of water using pebbles for support. More extensive forcing projects are best done in clay or plastic pots that have adequate drainage holes.

Soil mix—Bulbs for forcing should not be planted in ordinary garden soil. Potting mixes that are labeled potting soil also should not be used. These mixes are often no more than a fine form of peat moss. This type of material holds too much moisture and often causes water-related disease problems. The most desirable mix is one containing equal parts of soil, spaghnum moss, and perlite or vermiculite. Commercial “soil-less” potting mixes also can be used.

Planting—Fill three-quarters of the container with potting mix. Spacing considerations that apply to planting bulbs in the garden do not apply when the bulbs are to be forced. Purchase enough bulbs to “fill” the container. Place tulip bulbs with the “flat” side facing the edge of the container. After you arrange the bulbs, place additional media around them. Do not fill the container to the surface with the potting mix. The tops of tulip and narcissus bulbs do not need to be covered. The bulbs should then be watered in.

Cold period—All of the spring-blooming bulbs, with the exception of paperwhite narcissus, must have a cold period of at least three months to initiate bloom. You can supply this cold period in a variety of ways. Potted bulbs can be stored in a refrigerator. This method is only practical if an extra refrigerator can be devoted to bulbs for a three- to four-month period. Pots in a refrigerator tend to dry out rapidly so check them periodically to ensure there is enough moisture.

Bulbs can be chilled in a cold frame. If you use this method, make sure you open the cold frame on sunny winter days. Even when the outside temperature is under 40°F, the inside of the cold frame can rapidly heat up, which can initiate early flowering.

A simple method involves chilling the pots under natural cold conditions outdoors. Dig a trench or pit in the vegetable or flower garden approximately as deep as the containers. Place pots in the trench or pit and cover with loose, dried leaves; straw; or spaghnum moss. Then cover the mound with plastic, and anchor it with soil, bricks, or rocks.

The leaves, etc., act as a buffer zone. Bulbs will receive the cold temperatures they need but won’t freeze. It isn’t absolutely necessary to cover the pots with plastic, but it makes it much easier to remove the pots after the cold period has been completed.

The length of the cold period needed depends on the specific bulb and, in some cases, the cultivar. The following table gives cold treatment guidelines for bulbs that are easily forced.

Crocus - 15 Daffodil - 15 Glory of the snow - 15 Grape hyacinth - 14-15 Hyacinth -n 11-14 Iris - 15 Iris reticulata - none Iris danfordiae - 14-20 Paperwhite - none Tulip - 15-17

Forcing—After bulbs have been chilled long enough, bring the pots indoors for forcing. Check the pots to see if the bulbs have produced an adequate root system. (Look to see if any roots are visible through the drainage holes.) The number of weeks it takes before the plants actually bloom depends on the environmental factors in the home, but the average is two to three weeks.

Indoor Care-When you bring pots indoors, clean off excess garden debris. Water pots thoroughly. Place pots in a cool area of the home (high light intensity is not important at this point). Leave pots in a cool location until active growth is visible. Take care not to over water. Once active growth begins, you can move the pots to a warmer location that receives more light.

Forcing bulbs slowly is more desirable than placing them directly in a bright, warm location. The quick transition from chilling to warm temperatures can sometimes “blast” the buds, which means everything moves too fast and the bulbs do not bloom.

Because of the warmer indoor temperatures, flowers from bulbs that are forced indoors do not last as long as outdoor flowers. Forcing several containers of bulbs on a staggered schedule extends the indoor display.

After-bloom Care—Forcing is hard on most bulbs. The easiest after-bloom care is pitching the bulbs on the compost pile. If you wish to recycle these bulbs for the garden, after-bloom care is critical. The key to success is keeping the foliage actively growing as long as possible.

Bulbs will need to be fertilized with a water-soluble fertilizer. (Follow label directions.) After the foliage has died back naturally, the bulbs can be planted directly in the garden or stored for later planting. If they do not perform well in the garden, do not be disappointed.

Forced bulbs are most useful for indoor enjoyment. By all means, do not try to force the same bulbs the next season. It is difficult to re-create the natural bulb cycle indoors. Most homes simply do not have the necessary light conditions to be successful.