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Forcing bulbs

October 21, 2010
By Stephanie Bethke-DeJaeghere

It is that time of the year when most of us are adding a few spring blooming bulbs to our gardens. Forcing bulbs is a process that actually stimulates bulbs to bloom out of season. Cornell University has some really great information regarding this process.

The commonly forced bulbs are amaryllis, paper-white narcissus, muscari and hyacinths. You can also try your hand at other bulbs as well such as colchicum and miniature iris. These, however, are a bit more of a challenge. Spring flowering bulbs usually require a rooting period of about 12 to 15 weeks at temperatures between 41-48 degrees. Amaryllis and paper whites do not require this period in order to be forced into bloom.

Pot your bulbs right away and keep them in an old refrigerator, a root cellar or cool basement. The best way to store them is in a mesh bag or paper bag with holes that permit ventilation. This is only necessary if you can not plant them immediately. Plain potting soil works well and the best show comes from those plants that are crowded with bulbs. They can touch each other, if necessary. Different bulbs require different periods of time to root well.

This is why you will see the same type of bulbs planted in the same pot. Bulbs will flower about 3-4 weeks after they have been brought into warmer temperatures. So, 12 weeks or so for root development and then another 3-4 weeks until you have actual flowers. To flower in January, plant your bulbs in September or early October or to flower in February, plant early to mid-October and if you want them to flower later, then plant in late October or early November.

The exceptions to the rules are paper whites and amaryllis.

The one key step is that you cannot store spring flowering bulbs in a paper sack, plant them and expect them to flower. They need to be in a pot. Another key element to forcing bulbs is that once they get to the 12 week period for root growth, they should be moved to an area that gets indirect sunlight and the temperatures are about 60 degrees.

Once you note that the shoots are about 4-6 inches tall, move the pot into a bright, sunny window to stimulate blooming. A temperature of about 68 degrees and direct sunlight will produce the best results. Once the blooms start to have color, then return them back to an area where they have indirect sunlight to make the blooms last longer.

Amaryllis bulbs are different. Fertilize once a month during active growth. After the flower is done blooming, cut off the stems just above the bulb nose. During the summer months, move it outdoors and keep it watered and fertilized. In September or October, bring the pot indoors and stop watering it. Keep it in its pot and keep it in a closet for about 10 weeks. After 10 weeks, add a little fresh potting soil or repot the plant. Water thoroughly to get the bulb started up again but after the initial watering, water only sparingly until you see growth.

The amaryllis should start to flower in about eight weeks. A tip with amaryllis is to keep the bulbs away from ripening fruit which emits ethylene gas and can damage flower development.

Paper whites, or colchicum do not require the 12 week rooting period. Paper whites can be easily potted in shallow containers of gravel. Place the container in a sunny spot and water them just enough that the water level will go just to the base of the bulbs. Roots develop quickly (you should see them in a day or so) and in about three weeks to five, you should see flowers.

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