Bulbs can store energy (food) in the form of starch to fuel their seasonal growth cycle. Because they contain a miniature plant with flower, stem, leaf and root parts, bulbs are ready to spring forth when conditions are right. Many bulbs native to tropical climates adapt well to classroom conditions and, with minimal care, will produce resplendent flowers during our winter months. Others, typically planted outdoors in fall, your students can simulate or "force" to bloom indoors during winter.
You can purchase (or try to get donations of) flowering bulbs in the fall at nurseries, garden centers, and through mail order catalogs. When buying spring-flowering bulbs such as daffodils, tulips, crocuses, or hyacinths, buy, if available, ones labeled "good for forcing." Pick bulbs that appear smooth and firm and feel heavy. Very inexpensive bulbs are sometimes small and may take a long time to bloom, or produce fewer blooms.
Materials and Planting
If you can't plant your bulbs as soon as you get them, store them in a cool (35 to 50 degrees F) spot until ready to plant. Whether you're growing tropical bulbs like amaryllis or forcing spring-flowering bulbs, you can use any type of well-drained containers. One teacher reported a successful bulb project using recycled plastic containers from a local deli. Barbara Dixon's 1st graders in Loveland, OH, raised crocuses in recycled school milk cartons. Containers should be about twice as deep as the length of the bulb.
You can grow bulbs in a commercial, well-drained potting mix. Should you want to make your own mix, try combining one-third commercial potting soil, one-third peat moss, and one-third sand or perlite. To improve drainage, consider covering the drainage holes in the bottoms of the boots with pebbles, rocks, pot shards, or white plastic "popcorn" used in shipping. Then fill the container half full of moist potting mix and set each bulb with it's flat end down and it's tip half an inch below the pot rim. You can but more than one bulb to a pot as long as you leave half an inch between bulbs and to the edge of the pot. Continue adding soil until only the tips of the bulbs are showing, then water thoroughly.
Coaxing Spring Bulbs
Spring bulbs are typically planted in the ground in the fall where they spend a cold winter, not resting but growing roots which give them a head start on the spring. Because true bulbs contain a miniature plant and stored food (starch), they're ready to spring forth when conditions are right for flowering. By simulating the natural conditions that bulbs experience outside, you and your students can coax bulbs to bloom during mid-winter.
Why not challenge your students, as a class or in small groups, to brainstorm how to provide a "winter" for your potted bulbs? If you have enough bulbs to spare, have students test several of their ideas, even those you think may not succeed. Ideally, the potted bulbs should be kept at temperatures between 35 and 50 degrees, and placed in paper bags or under boxes or burlap to exclude light. Consider leaving them in a cool cellar, unheated garage, or refrigerator, or buried in a cold frame under soil or leaves. Check to soil every four weeks, and water if it's dry to the touch.
Leave the bulbs under these cold conditions for 10 to 15 weeks by which point a root system and small pale shoots will have emerged. To encourage strong shoots and to acclimate them to their new conditions once you bring them out, keep bulbs out of direct sun or bright light for several weeks. Water when dry to the touch and watch as the white shoots turn green as they photosynthesize. As soon as flower buds appear, put them in brighter light on a windowsill or GrowLab. Once the flowers bloom, in about 2 to 3 weeks, less direct light and cooler temperatures will encourage them to bloom longer.
Although most bulbs cannot be forced to bloom indoors more that once, many stand a chance of blooming the following year if planted at the recommended depth outdoors once the weather has warmed in the spring. (Note: tulips that have been forced will typically not bloom again.)
Paperwhites -- No Need to Chill
Paperwhite narcissus can be forced to bloom in the winter without cooling. Thy do best when planted in a container without drainage holes, filled with pebbles to one inch below the rim. Add water to barely below the top of the pebbles, then set bulbs on top and add enough pebbles to cover a third of the bulb. Maintain that water level and leave the bulbs in a cool location with little or no light for a week or two. Tug gently on the plants from time to time to test for root development. Once they feel rooted, move them to a well-lit spot without direct sunlight. They should flower in 3 to 5 weeks.