Forcing Flowering Bulbs
Choosing the Best Bulbs for Forcing
Not all varieties of bulbs work for indoor forcing. In general crocuses, daffodils, grape hyacinths (muscari), hyacinths, paperwhite narcissus or tulips are good choices for forcing. Below is a short list of good varieties to force:
- Daffodils: Dutch Master, Mount Hood, Tête-à-Tête, Large Cup Carlton, Ice Follies
- Paperwhite Narcissus: Ziva, Inbal. These don't need pre-chilling.
- Hyacinth: Delft Blue, Jan Bos, Orientalis Mix, Aida
- Crocuses: Pickwick, Mammoth Yellow, Large Flowering Mix
- Tulips: Tulip Affaire, Tulip Hemisphere
In addition to choosing the right variety, choose bulbs that are firm, large (for that variety) and undamaged.
Container and Soil Selection
The container can be made out of any material but should be twice as deep as the bulbs you are planting and have drainage holes. Pre-chilled hyacinths can be placed in a special hourglass-shaped vase filled with water.
The soil is primarily for anchoring the bulb and providing moisture. A good well-draining potting soil is fine but a special mix of one part garden soil, one part peat and one part perlite can also be used. Paperwhites can also be planted in small pebbles, marbles or soil.
The bulb contains all nutrients needed to grow, so additional fertilizer is not needed.
How to Plant
Here are general guidelines to planting:
- Partially fill the container with soil, place the bulbs on the soil and adjust the bottom soil level to so the tips of the bulbs are even with the rim of the container.
- Put the blunt end of the bulbs in the soil. Don't press them into the soil, it might cause damage.
- Place the bulbs in densely. Fill in with enough soil so just the tips are showing for tulips and half the bulb for daffodils. Crocuses, snowdrops and grape hyacinths should be set one inch below the soil surface.
- Water thoroughly and get ready to chill.
Chilling the Bulbs
The potted bulbs need to be exposed to chilling temperatures between 40-50 °F for 12-16 weeks. This allows time for the roots to grow. If root growth is inadequate due to insufficient chilling, the flower may be abnormal.
Outdoor storage - dig a trench deep and wide enough to accommodate the pots. Make sure the pots are sitting on something so they won't be floating in water (gravel, saucers turned upside down...). Cover with straw or a tarp.
Indoor storage - Dark basement of root cellar will work as long as the temperature is between 40-50 °F. If chilling in a refrigerator (must be kept dark), don't store near fruit such as apples. They give off ethylene gas which can inhibit plant growth and flower development. Also beware of freezing zones in the refrigerator and keep the soil moist.
Check after about 10 weeks for root development. Roots should be emerging from the drainage holes. Yellow shoots should also be sprouting from the bulb. If the bulbs are bigger, like daffodils or large tulips, check after twelve weeks.
If you have good root growth, the bulbs are ready for forcing. Move the pots to a warmer (50-60°F) location that receives low to medium light until the leaves start to turn green, usually 4-5 days. After this time, move to a bright, warm location (60-65°F) like a sun porch or sunny window. After about 3-4 weeks you should be rewarded with beautiful flowers. For a succession of blooms, bring in a few pots every 2 weeks. The blooms will last longer if kept in a cooler location.
Enjoy springtime in the winter by forcing some bulbs. These bulbs can't be forced again the following year. Some say to discard the bulbs but try putting them out in the garden in the spring. You just might get some flowers in a couple of seasons.
- Forcing Bulbs for Indoor Bloom, Purdue University Cooperative Extension Service
- Forcing Tulip Bulbs Indoors, Iowa State University Extension and Outreach
- Forcing Bulbs, Wisconsin Horticulture, University of Wisconsin-Extension