Here's a seasonal tip from the archives of Growing for Market. (I am just now trying this myself, so I can't vouch for its success. If you want to experiment, read the directions carefully and try it on only a few bulbs.)
The paperwhite narcissus is a popular bulb for winter forcing, but often the stems get so tall they flop over before the plant has finished flowering. New research reveals an unexpected solution to the problem: watering with alcohol.
William Miller of the Flowerbulb Research Program at Cornell University found that paperwhites watered with dilute solutions of alcoholic beverages will be one-third to one-half shorter, with flowers as big and long-lasting as usual.
Miller suggests planting paperwhites in stones, gravel, marbles, glass beads, etc., as usual. Add water as you normally would, then wait about one week until roots are growing and the shoot is green and 1-2 inches above the top of the bulb. At this point, pour off the water and replace it with a solution of 4-6% alcohol made from just about any hard liquor such as gin, vodka, whiskey, rum, or tequila. To get a 5% solution from a 40% distilled spirit such as the aforementioned, add 1 part liquor to 7 parts water. Do not use beer or wine, as the sugars will cause problems for the plant. And don't exceed the 6% alcohol solution as any more may be toxic. If you don't have liquor in the house, you can use rubbing alcohol, which is 70% alcohol, and may be diluted at the rate of 1 part rubbing alcohol to 10 or 11 parts water.
Use the alcohol solution instead of water for further irrigation of the bulbs. The plants will start to show effects within just a few days.
Researchers aren't sure why the alcohol stunts the plant's growth, but suspect it is simply water stress, in which the alcohol makes it difficult for the plants to absorb water.