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Forcing Bulbs for Winter Bloom Indoors

Posted: December 13, 2016

Colorful flowers can be yours throughout the winter if you act now.
Photo Credit: Julie, Penn State Live

Photo Credit: Julie, Penn State Live

A pot of amaryllis (Hippeastrum spp.) at Christmas, paperwhite narcissus (Narcissus tazetta) in early January, Dutch hyacinth (Hyacinthus orientalis) before the end of February and bright, yellow daffodils (Narcissus spp.) in the middle of March are a few examples of how you can fool Mother Nature by forcing flower bulbs for indoor bloom. Amaryllis and paperwhite narcissus make lovely Christmas gifts and you can give spring bulbs for Mother’s Day and for spring weddings.

The Meaning of Forcing

Forcing means causing bulbs to flower in other than natural conditions. The word ‘bulb’ is not always accurate but we use it as a simple way of referring to true bulbs, corms, tubers, tuberous roots and rhizomes. They all store food to nourish the plant no matter the environmental conditions. It is important to know that there are two types of bulbs for indoor forcing: those that need a cold period and those that do not.

Bulb Forcing Without Cooling

The easiest bulbs to force are those such as amaryllis and paperwhite narcissus that do not need a period of cooling.

  • Amaryllis
    You may purchase pre-planted bulbs in starter kits; however, it is simple to plant your own amaryllis. Choose large, firm bulbs free of cuts or bruises, remembering that larger bulbs have larger flowers and produce more flowering stalks. Use a container that is twice as deep as the bulb itself, allowing about an inch all around the bulb’s sides. The pot must have a drainage hole. Fill the bottom of the container with two inches of soilless potting mix. Center the bulb and add potting mix around it so that a third of the bulb is sticking above the soil level.  Water well and place in a warm, sunny spot. Then water sparingly until the first sprouts appear when you can begin watering more frequently. Rotate the pot every few days to keep the stems growing straight. Beautiful flowers will open after six to eight weeks. They will bloom longer if you place the pot in the coolest part of your home.
  • Paperwhite narcissus
    Paperwhite narcissus, its yellow cultivar ‘Soleil d’Or’ and the Chinese sacred lily (Narcissus tazetta var. orientalis) are effortless bulbs to force. Use a three to four inch high pot with no drainage hole and add two or three inches of pebbles or pea gravel. Water to just below the surface of the pebbles. Place the bulbs close together in the gravel so they remain in place. The tips of the bulbs should be even with, or slightly below, the rim of the container. Place the pot in low light until the plants become rooted and some shoots appear. Bring the container gradually into direct sunlight such as in a south-facing window. Monitor to maintain moisture below the top of the gravel. Blooms will appear within three or four weeks. By making successive plantings of paperwhite narcissus every two weeks starting this month, you could have flowers by Christmas through the end of March.

Bulbs Needing a Cold Period Before Forcing

Hardy bulbs such as daffodil, grape hyacinth (Muscari armeniacum), Dutch hyacinth, and tulip (Tulipa spp.) should be cooled after planting in a container. (Some bulbs are precooled so check the bulb package.) The method for forcing bulbs that need cooling is as follows:

  1. Containers and Potting Mix
    Choose a container (with a drainage hole) that is twice as deep as the bulbs. As with amaryllis, use a soilless potting mix.
  2. Planting
    Put about two inches of mix in the bottom of the pot. Plant larger bulbs (like daffodils) with their tips showing above the potting mix and smaller bulbs (such as grape hyacinths) with about one inch of soil on top. Do not pack the mix down too much to allow good drainage. Plant the bulbs closely together, but not touching, in order to ensure more flowers at bloom time. Place tulip bulbs with their flat side toward the outside of the pot as this will create a uniform appearance when their first leaves emerge. Water immediately and do not allow the soil to become dry afterward.
  3. Cooling
    Cool your bulbs in a location where the temperature is 35 to 55 oF. It should be a cool, dry place with enough humidity to prevent the bulbs from drying out. A basement, unheated garage or the crisper drawer of a refrigerator work well. Cover the pots with plastic bags in which you have punched holes before putting them in the refrigerator. Avoid placing pots near fruit because it produces ethylene gas that may cause the bulbs to deteriorate. Cooling times depend on the bulbs: daffodils need a minimum of 13 weeks, grape hyacinth a minimum of 14 weeks, Dutch hyacinth a minimum of 10 weeks, and tulips need 14 weeks minimum. Mark your calendar to keep a record of when to stop cooling and start forcing.
  4. Forcing
    Bringing the pots into warmth and light triggers the growth of leaves and flowers. Place them in indirect sunlight with a temperature of about 60 oF until the shoots are four to six inches tall, then move them to a bright sunny window at about a 68 oF temperature. Return them to indirect sunlight when the buds are beginning to open to make them last longer. On average your bulbs will flower in three to four weeks.
  5. After Care
    After blooming, discard your forced bulbs, as they are unlikely to bloom again – amaryllis being the exception. After the last frost, put your pot of amaryllis in a sunny spot outdoors. Cut off all the leaves in early fall, stop watering and allow the plant to rest for two months. In late fall begin the forcing process all over again.
Forcing bulbs is inexpensive, easy and fun. It is refreshing to see a pot of spring flowers on the windowsill when the snow is still falling. Their cheerful blooms regenerate my determination to survive another Pocono winter, reminding me that spring will eventually return. 

Contact Information

Pamela T. Hubbard
  • Penn State Master Gardener of Monroe County