ARTIFICIAL ‘NIGHT’ FOOLS POINSETTIAS INTO BLOOMING NEAR CHRISTMAS
Early winter is when poinsettias come into the limelight, showing off their colors in homes and shop windows. But a poinsettia is more than just seasonally flamboyant.
To check out more of this plant’s botanical flair, set your holiday poinsettia on a table in good light so that you can look closely at its flowers. The flowers are not those large, red, leaf-like structures; those are just that — modified leaves called bracts. The bracts are for attracting pollinating insects.
The flowers are in the cyathiums, the little, greenish, cup-shaped structures above the bracts. Each cyathium contains a single female flower surrounded by a harem of males.
Have you ever wondered how stores always manage to have blooming poinsettias for the holiday season? The poinsettia can be fooled into blooming at any time of year merely by exposing it to artificially shortened days.
Along with chrysanthemums and most strawberries, poinsettia is a “short-day” plant. That is, short days induce it to form flower buds. (“Short-day” plants actually are responding to long nights, but the phenomenon was originally thought to depend on day length, and the term stuck.)
To bloom for Christmas, commercial poinsettias are given artificially long nights by being covered with shade cloth. You can use this trick to make your poinsettia bloom again whenever you want. But first, your plant needs a rest. In the weeks following the holiday season, dropping leaves and fading flowers will tell you that it wants to be left alone, watered just enough to keep its stems from shriveling.
The plant should start to perk up in about April. Shorten the stems and give it good light — preferably outdoors, once the weather warms — and fertilizer and water as needed. In late summer, move the plant back indoors, to a sunny window.
Begin the light treatment three months before you would like the plant to bloom. Make sure it gets 14 hours of uninterrupted darkness daily by moving it into a dark closet or covering it with an opaque bag.
After eight weeks, flower buds will be evident, and you should have a blooming poinsettia within a month. If you want it to bloom for Christmas next year, start the light treatment in the middle of September.
Poinsettias, like other members of the spurge family, ooze a white sap when their leaves or stems are cut. That sap is bitter and irritating and can cause stomach upset, but, contrary to popular myth, it is unlikely to be fatally toxic to a dog or cat.
Reich writes for The Associated Press.