Plan now for beautiful blooms in the middle of winter! Forcing provides the proper temperature conditions to allow bulbs to flower indoors, usually much earlier than would happen naturally outdoors. Paperwhite narcissus and amaryllis are the easiest bulbs to force and don’t require a long time for rooting. You can have blooms of paperwhites in 3-5 weeks, while amaryllis can bloom in 6-8 weeks. Other spring-flowering bulbs require a longer conditioning period to induce bloom. Plant batches in succession and you’ll enjoy fresh flowers throughout the season.
Paperwhites are often forced in a shallow pot or bowl (without drainage holes). A clear container lets you see the roots developing and makes it easier to gauge the water level. After filling the pot about two-thirds with pebbles, gravel or soil, place as many bulbs (flat end down) in the container as will fit without touching each other. Then fill in around the bulbs. Add water to the pot until it just reaches the bottoms of the bulbs. Place the container in a cool, dark spot (45-50°F) to encourage root growth.
In about three weeks, after roots have developed, move the pot to a cool, sunny spot. Sprouts will quickly develop and soon thereafter blooms. Keep the water level just at the base of the bulbs. The fragrant flowers will last 10 days to several weeks in cool conditions (less if it’s warm). You can adjust the bloom time a little, by adjusting temperature and watering. If the plants are developing too quickly, move them to a cooler spot and reduce watering but if you need to speed them up, put them in a warmer place. You can stake the stems if they start to flop over.
Plant amaryllis (Hippeastrum hybrids) bulbs in containers with a drainage hole (and saucer to catch water run-off). These large bulbs are often potted individually in a pot an inch or two larger in diameter than the bulb but several can be combined if you have a large enough container. Soak the bulbs and roots overnight in lukewarm water before potting. Place a layer of gravel in the pot and add a few inches of soilless potting mix. Place the bulb on top of the potting mix so that the top of the bulb is barely above the rim of the pot and fill with more potting mix around the bulb, leaving the neck exposed. Water well and place in a cool, sunny spot. Water sparingly until a sprout forms, then water more frequently to keep the soil moist. It will take six to eight weeks for the plant to bloom.
All other spring-flowering bulbs need a longer period of chilling to bloom. Crocus, daffodils and tulips are all suitable for forcing but some varieties work better than others (and are often listed as suitable for forcing in catalogs). Shorter varieties tend to make a better indoor display and won’t flop over as easily. Regardless of the type or variety, use the largest bulbs you can get since the flowers will be larger. Tulips tend to be more difficult to consistently force with daffodils less so. ‘Tete-a-Tete’ is a very good variety of small daffodil for forcing. Hyacinths, crocus and grape hyacinths are easier to force.
Preparing the bulbs for forcing is simple. Choose pots with a drainage hole(s) and fill the containers partway with a light, well-drained soilless potting mix. (You may want to put a layer of gravel in the bottom of the pot before adding the potting mix.)
Place as many bulbs as you can in the pots without them touching each other or the sides of the pot – crowding them in gives a better show of flowers. Add enough potting mix over the bulbs so they are sticking out of the soil about halfway. Water the pots well.
The planted pots then need to be chilled for 12-17 weeks at 40-50°F. You can just place them in a refrigerator but some people have good results keeping them in an unheated garage or a cold frame as long as the temperature doesn’t drop below 20°F. Too much freezing and thawing will cause the bulbs to rot, so the consistent temperatures in a refrigerator ensures success. Check the pots periodically and water as necessary to keep the soil moist but not wet. If you’re using a refrigerator, you can cover the pots with an open plastic bag, which reduces the need for frequent watering. If you’re potting bulbs on more than one date, label the pots so you know when to take each out.
Two to four weeks before you want them to bloom, take the pots out of the refrigerator and move them to a warm spot in indirect light for a few days.
When the sprouts have greened up, transfer the pots to the sunniest window you have and continue to water as necessary. In early spring, containers can be moved outdoors as long as the weather is not too cold but the plants need to be acclimated to the change of conditions if they are near to or are already blooming. Forced bulbs can be combined with other cold tolerant plants such as lettuce or pansies.
If you want to plant your forced bulbs outside when they’re done blooming, cut off the flower stalks but leave the foliage until it’s completely dead. Then plant the bulbs outside at the appropriate time in the fall. It will probably take a year or two for the bulbs to bloom again.
If you don’t have room in the refrigerator for a bunch of pots of soil, try forcing hyacinth bulbs. Simply put them in a paper bag in the refrigerator for 4-6 weeks. Bring them out and put them in specially designed forcing vases filled with water just up to the base of the bulb. Place them in a bright window and in about four weeks you should have beautiful, scented hyacinth flowers!
– Susan Mahr, University of Wisconsin – Madison