Every December poinsettias appear, like an invasion of Christmas colors wrapped in plastic. But where do they come from? You never see poinsettia seeds in garden catalogs, or little poinsettia seedlings for sale in nurseries. Do they get dropped off from UFOs or manufactured by Santa’s elves? Nope- they’re just a pain in the butt to grow at home.
The tricky part of growing poinsettias is getting those colored leaves (bracts, really) to be large enough and to appear at the right time. Poinsettias are extremely sensitive to light and temperature, which makes them easy to manipulate in a well controlled environment, and difficult to work with at home. Because commercial growers can control when the plants are at their peak, they can target specific sale dates, such as Thanksgiving weekend. Growers are also very concerned with growing plants that are the perfect height, which is why poinsettias usually look like alien clones of each other, except for their color.
When I say poinsettias are picky about lighting, some people start to think about another ubiquitous houseplant in grocery store floral departments, the Christmas cactus (Schlumbergera). Christmas cacti need long nights in order to bloom. I leave my Christmas cactus in the kitchen, where it sees an indoor light whenever I cook dinner, but it still reliably blooms starting at Thanksgiving and peaks a bit before Christmas. Coaxing big, colored bracts out of a poinsettia under the same conditions would be nearly impossible. They need uninterrupted dark periods, and growers are careful not to ever flick the lights on in their poinsettia greenhouses at night, even for a minute. They’ve been carefully bred to be able to handle all-day fluorescent lights without losing their coloring, once they hit grocery stores and garden centers.
I don’t generally buy poinsettias, mostly because I prefer plants that keep giving year after year, like amaryllis bulbs. I also find it more satisfying to watch a plant go through its whole growing cycle, like watching buds form on the Christmas cactus, or seeing the shoot on an amaryllis emerge and then keep growing taller and taller. If you have a poinsettia this year, remember that in Seattle you can toss the dirt and the plant into your city compost bins, and the plastic pot into your recycling bin.
Enjoy whatever holiday plants keep you happy, and have a merry Christmas!