Why you've been in the dark about making your poinsettia bloom again

Poinsettias can be tricky, but it takes a rather counterintuitive trick in the fall to ensure they bloom again.

The key is to keep the plant in mostly darkness at a certain time of year

An Ontario based poinsettia grower displays varieties for the holiday season in 2016. (Roger Dubois/CBC)

So you want to keep that poinsettia alive and blooming for next year's holiday season?

 It's an uphill battle, but it can be done.  

"With the right care, poinsettias can stay alive for many years. The trick is to get them to bloom again," said Anita McDonald, partner at Kuhlmann's Greenhouse in Edmonton.

The key bloom period for poinsettia starts in late September and peaks in January.

McDonald explains the red parts of the plant that look like flower petals are in fact a variation of leaf called bracts, and the yellow bits in the middle are flowering buds. Keeping your poinsettia alive requires the acceptance that the bracts won't last all year. 

"The bracts that you have on your plant right now should last another month or two," says McDonald. "Then you probably want to look at pruning your plant."

McDonald suggests cutting the stems back in March to about a third of the length.

"This will start to create lots of new growth through when our days get longer," she said, adding that water about once a week is all the plant needs during the winter months.

Darkness is the key

There's one counterintuitive step that most people miss when trying to encourage their poinsettias to bloom again — keeping the plant in the dark. 

"They need at least 12 hours of darkness a day," McDonald said. "They say even a streetlight outside your window can be too much light."

Jim Hole owns Hole's Greenhouse and Gardens in St Albert, which produces about 50,000 poinsettias each year. He said growers need to make sure that poinsettias are getting more darkness than daylight during the bloom cycle. 

They need 12 hours of darkness a day.- Anita McDonald, partner at Kuhlmann's Greenhouse

"You can put them in the closet at night to ensure you have uninterrupted darkness, but then it's critical to get them out into the light so they can keep producing growth and they can absorb sunlight and grow properly," Hole said.

Gardening experts suggest leaving poinsettias in a closet between 8 p.m. and 8 a.m. from late September to early December.

Locally grown

The poinsettia, Latin name Euphorbia pulcherrima, is native to Mexico and parts of Central America, growing best in United States Department of Agriculture (USDA) plant hardiness zones 8 - 11

Mexico and Alberta are in disparate plant hardiness zones, making poinsettia care difficult in Alberta. (United States Department of Agriculture)

In the home, both McDonald and Hole recommend keeping the plant away from hot and cold drafts.

"Poinsettias like it fairly warm and like humidity," said McDonald. "Keep them away from heat registers that may be blowing dry air."

As for water, McDonald says it's important to keep the soil moist but not saturated.

If you have to move the plant to another building, wrap it up from the cold in a layer of paper then plastic.

Dangerous for pets?

While poinsettias are cited as a plant that is dangerous to pets, Sherwood Park veterinarian Dr. Louis Kwantes said poinsettia poisoning is not a major concern.

"They do cause irritation, you may see some hypersalivation or maybe even a little bit of vomiting or some gastrointestinal upset," said Kwantes.

At this time of year, Kwantes says mistletoe and daylilies are more toxic to pets than poinsettias.

"Obviously, keep your pets away from [poinsettias] but by and large if they do get into it, unless there's an underlying disease or problem going on, there shouldn't be a big issue," he said.

About the Author

Tanara McLean is a producer and journalist at CBC Edmonton. She grew up in Red Deer and has spent her entire career in Alberta, working in print, radio and television.