Forcing Bulbs

Spring bulbs can be "forced" into bloom in containers. Forcing is a term used to describe manipulating bulbs to bloom ahead of their natural time. To avoid disappointment, it is important to understand that for most bulbs forcing involves giving the plants a period of artificial winter when they actively root. There are only a few bulbs that will bloom without a cold period. Persuading bulbs to bloom for you indoors can be fun if you follow a few basic steps to insure your success.

Which bulbs will bloom without forcing? Amaryllis and paperwhite narcissus are the easiest of all bulbs to bring into bloom. Neither requires any cold treatment and will bloom within weeks of planting. Ask for a care sheet for complete information on amaryllis and paperwhites.

Which bulbs require a cold treatment? The best bulbs for forcing with a cold (and dark) treatment are tulips, daffodils, hyacinths, crocus, grape hyacinths and species iris. Chionodoxa, freesias, scilla and a few other minor bulbs can be forced, too.

Why do some bulbs need cold treatment? Most bulbs are programmed by nature to wait until they have developed a complete root system before sending up their blooms. If we don't give them an adequate amount of time at the right temperatures, the bloom will come up but will usually be short and distorted.

How long do the bulbs need to be chilled? This varies from 6 to 15 weeks, according to the variety of bulb. Tulips need the longest cold period, taking from 14 to 15 weeks to root fully. Daffodils take slightly less time, 12-13 weeks. Hyacinths and crocus require 10-12 weeks. Scilla and muscari (grape hyacinths) need 8-9 weeks. Chionodoxa, freesias and iris reticulata require 6-8 weeks. These bulbs need to be fully rooted to bloom properly.

What temperature is needed to force bulbs? For forcing at home, keep the potted bulbs around 40º. Since this is the average temperature in most home refrigerators, it works out great. When forcing bulbs in the refrigerator, be sure to keep them moist (this may be a problem with frost-free units). Also, keep in mind that ripening fruit gives off a gas that can cause buds on bulbs to abort or deform.

Can I force bulbs without a refrigerator? Pots can be sunk directly in the ground or placed in a cold frame and covered with enough loose soil and straw the keep them from freezing. When the bulbs freeze, they stop the rooting process.

Can I force them in the garage or basement? Lots of people try to force bulbs this way, but very few succeed. Usually the basement isn't reliably cold enough and the garage fluctuates between being too warm and too cold, resulting in bulbs that send up undeveloped blooms.

What is a "preconditioned" or "prepared" bulb? All this means is that the first few weeks of chilling have already taken place before you buy the bulbs. This does not mean you can force them without the cold period, but they should root out 2-4 weeks earlier.

Are all varieties of tulips and daffs suitable for forcing?
Some varieties are much better to force than others and it is usually marked on the packages. Generally, the best varieties for forcing are the ones that are early and short. A partial listing is provided at the end of this information sheet, but don't limit yourself  -
be adventurous.

Can I plant more than one kind of bulb in a pot? Blooming dates and chilling dates vary too much between bulbs. Planters that you see with crocus, daffs, tulips and muscari blooming at the same time have been put together at the last minute with individually forced bulbs. If you don't mind the crocus blooming first and then the tulips or daffs, you can plant them together and chill the grouping for the longest time required for any of the bulbs.

How should I plant the bulbs? Pot the bulbs in clean containers using a good potting soil. Shallow containers require less soil and look best with bulbs, but there should be at least an inch below the bulbs so they won't lift themselves up as the roots develop. Place an inch or two of soil on the bottom of the pot. Press the bulbs gently into the soil, spacing them so that they are almost touching. Add more potting soil until just the tips are showing. Other than points go up, there is no real trick to planting bulbs. The one exception is that the flat side of tulip bulbs should be planted toward the outside of the pot, since this is where the largest leaf will emerge.

Once they are planted, how should I care for them? Bulbs should be thoroughly watered after they are planted and then placed in your cold area. Mark on your calendar when the bulbs should be finished rooting. Check occasionally to make sure they are staying moist. If a mold develops, use a liquid fungicide.

What's next after they have cooled the right amount of time? Bring the bulbs out of the fridge and place them in a cool, sunny location and they will be in bloom in a matter of a few weeks. As the plants develop, you can move them to a warmer location. Providing extra light, such as fluorescent or grow lights, will help keep forced bulbs shorter. Generally, the closer to true spring, the more quickly they will come into flower. For a continuous supply of flowers, bring pots in at weekly intervals. Once they begin to bloom, the flowers will last longer if they are cool at night.

Can I save the bulb after they have been forced? Unfortunately, it is difficult to keep the bulbs in good enough condition to be able to reuse them successfully. It is much less frustrating to simply consider forced bulbs as a single use plant.