Here’s the skinny on poinsettias, and why I buy mine every year instead of growing them. First, poinsettias are known as a short-day, or photoperiodic, plant. That means they can’t be exposed to more than 12 hours of daylight. If they are, they will not initiate flowering to eventually turn that beautiful red color. The plants will stay in a vegetative state. By the way, what looks like a flower on a poinsettia is actually a cluster of small flowers surrounded by leafy bracts. A bract is a modified leaf that may be highly colored, like on poinsettias.
A commercial poinsettia grower purchases rooted cuttings from specialty growers for the purpose of producing stock plants sometime between March and May. The stock plants will be grown in 6-to 8-inch diameter pots until August to late September, when they will be used for propagation. At this time of year, the day length is still short enough to produce flowers (remember the 12 hours or less rule), so the grower must extend the day length to keep the stock plants from developing flower buds. No, they don’t do as Joshua did in the Bible, and ask God to keep the sun in the sky so he could finish his battle. Instead the growers take a simpler approach — a 60-watt incandescent bulb. These bulbs are placed 3 to 4 feet above the plants and turned on from 10 p.m. until 2 a.m. every night. This is enough light to fool the plant into thinking days are still long, thus no flowering is initiated.
The plants grow fastest when night temperatures are 65 degrees and day temperatures are 80 degrees, but not above 90 degrees or plants will stall. By the time summer has arrived, the days are long, so the need for the incandescent bulbs is gone. The stock plants will stay vegetative for now. From August until mid-September, cuttings are taken from the stock plants. Any later and there won’t be enough time for plants to grow before Christmas. As day lengths get shorter again, out come the incandescent bulbs. The grower needs the vegetative growth first, and then the color. Again, the plant is fooled into thinking day lengths are longer, and continue to grow and not flower. This produces compact, lush and full plants. Nobody wants a tall, skinny poinsettia.
The bracts are the reason we buy poinsettias and the time we buy them is very specific. You probably aren’t going to buy a poinsettia in July. You likely will buy one in November and December. The plants need to be ready to adorn Holiday tables — this means healthy, full, red, white or pink poinsettias ready in time for the holidays, just like your festive dinner.
From October until Thanksgiving, your grower is fertilizing (poinsettias need lots of fertilizers); maintaining proper temperatures; watering; pinching shoots on a schedule to get good growth; turning lights on and off to prevent flowering (or to initiate flowering); and watching for unwanted light from street lamps or shopping malls that may interfere with the plants’ growth.
White flies are an issue too. They can wipe out a producer’s crop, so scouting for those insects is a full-time job. Spacing the plants (while using every available square inch of space for more crops, which equals more money) is important for air circulation. And last, the growers prepare for market.
Poinsettias, which hail from Mexico, do not like the cold, yet they are a winter plant in the eyes of American consumers. Shipping them to market is no easy deal. An unprotected plant can be damaged by the cold in the short time it is carried from the greenhouse to a car. Sleeves are used for protection, put on by the grower before shipping them out.
So, after purchasing rooted cuttings which become stock plants for propagated plants, which eventually become the plant we purchase for our Holiday tables, surely the grower goes home and takes a long winter’s nap.
— Cinthia Milner gardens in Leicester.