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Bulb Forcing Tips and Techniques: Home

Purple Hyacinthus (hyacinth); photo by Mark Pfeffer
Purple Hyacinthus (hyacinth) forced indoors at NYBG; photo by Mark Pfeffer


Forcing is a technique that imitates the environment bulbs encounter outdoors, thereby tricking them into flowering earlier. Most bulbs need to experience a cold period to flower successfully. Different types of bulbs require different chilling periods, generally 12 to 16 weeks. As long as they have had the minimum time that they need, the bulbs should perform well.

For chilling, the basic requirement is a cold, dark space where the temperature is below 50°F and above 32°F; generally 40 to 45°F is best. An unheated garage or a cellar is usually an ideal spot. Cold frames and window wells are also suitable; cover the containers with dry leaves or several inches of straw and lay pine boughs on top to help insulate the bulbs. The vegetable compartment of your refrigerator is also a good option. However, do not store bulbs with fruit such as apples, which emit ethylene gas harmful to bulb growth. Store the pot in a plastic bag with air holes punched in it.

After the appropriate chilling period, the pots will start to show top growth and roots should be visible through the drainage holes. Bring the pots into a well-lit, unheated room (approximately 50 to 65°F) for about a week. If your basement is the right temperature but not bright enough, fluorescent lights will do the trick; you do not need direct sunlight during this phase. Bright light is best; you are mimicking the arrival of spring with increased temperature and light. If light is coming from one direction, rotate pots every other day to keep flower stems straight. After this adjustment period, you can bring them into a warmer area of your home, but temperatures in the 60s are best for the first 3 weeks until they are ready to flower.

Exposing bulbs to high heat too soon will cause the stems to flop and the flowers may not open. In general, don't place bulb pots close to heat sources; the cooler the location, the longer the bloom.

Bulb Planting Tips

  • Plant containers from September through November.
  • Select a pot with drainage holes. If you would like to display your bulbs in ceramic containers with no drainage holes (cachepots), you can plant the bulbs in a plastic pot and slide it into the ornamental container when ready for display.
  • Plant containers with a good commercial potting soil. All bulbs need good drainage.
  • Since the bulbs are in the containers for such a short time, feeding is not essential. They generally have enough food stored in the bulb.
  • Plant bulbs closely together in pots to create a full container, but give them enough space so that they are not touching each other.
  • Plant bulbs with the pointed end facing upward.
  • Cover bulbs so that they are just below the soil surface. After you water, the soil level will settle so that the tips of the bulbs are just poking above the surface.
  • Label your pots with type of bulb and the date of planting.
  • Water the pots thoroughly.
  • Unlike clay (terra cotta) pots, plastic pots do not "breathe." Water carefully so that they don't become waterlogged.
Tulips forced indoors on display at NYBG; photo by Mark Pfeffer
Tulipa (tulips) forced indoors on display at NYBG; photo by Mark Pfeffer

Bulb Types for Forcing

  • Tulip (Tulipa)

    bulbs are asymmetrical--one side is slightly flattened. The largest leaf of the tulip grows from this side. Therefore, plant the flattened side of the bulb facing the outside of your container. Tulips need a 14 to 16-week chilling period for best results. Good varieties for forcing are 'Apricot Beauty', 'Bing Crosby', 'Jingle bells', 'Attila', 'White Dream', 'Princess Irene', 'Monsella' and 'Estella Rijnveld'
  • Dwarf iris (Iris reticulata) and spring crocus (Crocus vernus)

    ideally need to be chilled for 10 to 14 weeks, but can be forced in as few as 6 weeks. Good varieties of crocus for forcing are 'Pickwick', 'Remembrance', 'Peter Pan', 'Flower Record', 'Jeanne d'Arc' and 'Purpurea Grandiflora'
  • Hyacinth (Hyacinthus orientalis)

    bulbs can be bought pre-chilled from some mail order catalogs and can be grown hydroponically (in water). If not pre-chilled, hyacinth bulbs need a chilling period of 10 to 12 weeks. If the bulbs come pre-chilled, they will still need a cold treatment, but a shorter one (the directions accompanying the bulb will specify the length of time). For hyacinths grown in water, place the bulb on the top of an hourglass-shaped hyacinth glass. The bulb should rest above, not touching, the water. Store in a cool, dark place for 4 to 8 weeks, and check to make sure that the water level does not drop. Once a good root system has developed, slowly bring the plant into warmth and light. Hyacinth stems are hollow, so if they start to bend over when flowering, you can stake them or insert a small piece of wire in them to keep upright. Good varieties for forcing are 'Amethyst',' Blue Jacket', 'Jan Bos', 'L'Innocence', 'Pink Pearl', 'Delft Blue' and 'Carnegie'
  • Daffodils (Narcissus)

    require a minimum cold treatment of 12 weeks but do best when chilled for 16 weeks. Miniature daffodils are ideal for forcing. Most daffodils require bright light to flower well; inadequate light results in leggy plants with few flowers. Good varieties for forcing include 'Barrett Browning', 'Bridal Crown', 'Dutch Master', 'Ice Follies', 'Salome', 'Pink Charm', 'Tete-a-tete', 'Jenny' and 'Cheerfulness'
  • Paperwhites (Narcissus tazetta cultivars)

    don't require a chilling period. To grow paperwhites, all you need is water, pebbles and a bowl or pot that is at least 2 inches deep and can hold 3 to 12 paperwhites. Fill the container halfway with pebbles. Place bulbs close to each other but not touching. Add more gravel until 1/3 of the bulb is covered. Fill with water until it comes just up to the base of the bulbs (pull gravel away from one bulb to see water level). It is often best to keep the bulbs in a cool, darker room (60 to 65°F) for several weeks until they are well-rooted before moving to a sunny location. Either way, the bulbs will flower in about 3 to 5 weeks.
  • Amaryllis (Hippeastrum)

    also doesn't require a chilling period. Plant them with at least 1/3 of the bulb above the surface and leave a 1-inch space between the bulb and the edge of the container. Water your amaryllis well after planting, but then keep the soil on the drier side until you see the flower stalk emerging. Once the flower stalk appears, start watering on a more regular basis. Amaryllis needs a well-lit, warm place to grow until the buds begin to open. Then it can be moved to a cooler, shadier location where the blooms will last longer. After the bulb finishes blooming, cut the flower stalk close to the base. Grow the plant in a sunny location and add houseplant fertilizer regularly. Stop watering and feeding in August, and allow the plant to dry out completely. It generally will need an 8-week resting period. In late September, cut back foliage and repot the bulb in fresh potting soil. Place in a sunny location and water sparingly until growth begins again.

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