Paperwhite narcissus are favorite bulbs for winter forcing. Their white or yellow blossoms are a lovely antidote to winter's bleakness. But unlike tulips, daffodils and other hardy bulbs that need to be tricked into thinking they've had a winter sleep before they'll bloom, these tender bulbs need no chilling period before producing their fragrant flowers. This makes them a great, easy choice to add color and fragrance to your classroom windowsill this winter.
You don't even need any soil – just place the bulbs, pointed end up, in a shallow pot filled with pebbles. Add enough water to just reach the bottom of the bulbs, set the container in a cool spot with bright light, and enjoy sweetly scented flowers in 2 to 6 weeks. Start pots of bulbs in succession and you’ll have plants coming into flower all winter long. (Bulbs forced in the fall will take 4-6 weeks to come into bloom; bulbs potted later in winter may bloom in as little as 2-3 weeks.) Forcing exhausts the bulbs and they aren't hardy in most parts of the country, so when the flowers fade, simply toss the bulbs onto the compost pile.
A common problem with forced paperwhites is that, in the warmth of our school rooms and homes and with the short, dark days of winter, their foliage grows tall and flops over. While you can keep leaves from tumbling with stakes and string, some enterprising researchers came up with a novel way to keep plants lower and sturdier – give 'em a drink!
Experiments done at Cornell University's Flowerbulb Research Institute found that when paperwhites were watered with a 4-6% solution of alcohol rather than pure water, the plants were 1/3 shorter and didn't need staking to remain upright, but the flowers were as large, fragrant, and long-lasting as usual. This technique seems to work by causing mild water stress for the plants, enough to stunt their growth somewhat, but not enough to affect flowering.
To try this technique, plant your bulbs and irrigate with water alone until the roots are growing and the green shoots are 1-2 inches tall. This usually takes about a week. Then pour off the water from around the bulbs, replacing it with a 4-6% solution of isopropyl (rubbing) alcohol.
To figure out how to make a solution of the correct dilution your students will need to use some simple math skills. Note the percentage of the alcohol (rubbing alcohol is usually 70% alcohol). To make a 5% solution, divide the percentage of alcohol by 5, subtract 1, and you have the number of parts of water (13) needed to mix with one part of rubbing alcohol. For a 4% solution, do the same calculation, but divide by 4, and so on for other dilutions. While the higher the concentration of alcohol, the shorter the plants, as with people, excess consumption is harmful. Don't go any higher than a 10% solution to avoid harming the plants.
If you’re forcing paperwhites at home, you may choose to use liquor instead of rubbing alcohol. Any hard liquor is suitable, such as gin, whiskey, vodka or tequila, but don't use beer or wine as the sugars in them can harm the plants. To figure out how to make a solution of the correct dilution, take the "proof" of the liquor and divide it in half to get the percentage of alcohol. For example, "80-proof" liquor contains 40% alcohol. Then proceed as detailed above.
For an interesting and easy experiment, have students start several pots of paperwhites at the same time. Water each with a different dilution of alcohol (be sure to water one pot with plain water as a control). Students can monitor and record the differences in growth and flowering and decide for themselves if “pickled” paperwhites result in a better show!