Poinsettias are ubiquitous holiday plants. I always feel like I need at least one to complete my Christmas decorating. Some years I go for the traditional red hue, others I opt for something more unique, like variegated leaves or bright pink bracts. Poinsettias are native to Mexico and Central America, so these tropical plants often don’t last in a home beyond the holidays. However, if they survived, it is possible to keep them for the following year and, after a period of darkness, get them to rebloom for you. So, if you’re wondering, when should I put my poinsettia in the dark, I will explain how to care for your plant throughout the year, until it’s time to display it once again for the holidays.
Trendy houseplants, like Monstera and Pilea may be popular, but the poinsettia is still the number one potted plant in America. Every year at my local nurseries, there are rows upon rows of poinsettias in different colors and shades of red. I’m willing to bet that a great deal of the 65 to 80 million (depending on which reports you read) that are sold each year end up in the landfill. So if you’re up for the challenge, why not try keeping yours around until next December.
How are poinsettias different than other houseplants?
What look like majestic petals on a poinsettia, are actually colorful bracts. Bracts are modified leaves that protect flower buds. On a poinsettia, you have to get really up close and personal to see the flower part of the plant. These little yellow and green spheres lie in the center of a bract and often look as though someone has added little flecks of gold to them as they open.
Like a kalanchoe or Thanksgiving cactus, poinsettias are what’s referred to as a “short-day plant.” The plant needs lower light levels to encourage it to rebloom. In the case of a poinsettia, the dark period after short days prompts healthy leaf growth and the bracts to change from green to the vibrant holiday red that is so popular (or whatever color it’s been bred to be). The aforementioned plants are a little easier to keep alive throughout the rest of the winter, spring, and summer.
Poinsettias are more finicky. They need to be protected from freezing temperatures just to get them from the store to your car, never mind the complexity of environmental growing conditions that are present in a modern home. If they’ve been well cared for where you bought them, they should at least survive the holidays. I’ve had years where my poinsettia was just not living its best life, despite my best efforts. Other years, it’s still gorgeous and lush come January. That’s the plant you’ll have the most success saving.
So, when should I put my poinsettia in the dark?
Not yet. After the holidays, the plant has just come out of its bloom cycle. It needs a chance to establish fresh growth before you put it in the dark.
Indoors, poinsettias need lots of light. When you first bring one home, keep your plant near a window where it will receive lots of bright, indirect sunlight during the day. But here’s the catch. It can’t be a drafty window. Avoid other warm and cold drafts from places like air vents and fireplaces. The temperature inside should be about 65°F to 70°F (18°C to 21°C).
Poinsettias need to be watered about once a week through the winter. Before watering, check the surface of the soil in the pot to ensure it’s dry. At this point I also remove any dead leaves that are sitting in the soil. Too much moisture can lead to root rot. But don’t let it dry out so much that it starts to wilt. I hold my plant over the sink when I water, allowing the water to drain out the bottom before placing it back in its decorative pot or foil after it’s sat on a plate for a bit. Before taking your plant home, some stores will recommend that you lightly mist the leaves and bracts regularly as the plants enjoy a bit of humidity.
Keeping your poinsettia alive beyond the holidays
In the new year, if you see new growth in January, add a half a recommended dose of water soluble houseplant fertilizer. I’ve seen green thumbs recommend a fertilizer high in potassium, like one you would use to fertilize tomatoes. Continue to fertilize every three to four weeks. If the plant starts to get a bit leggy, you can prune the stems back to about five inches (12 cm).
The trick in the summer is not to keep your house too cold with the air conditioning. Anything below 55°F (13°C) is too cold. A consistent temperature is best.
Before the summer, you may want to repot your poinsettia in new potting soil. I find the soil can get quite hard-packed. If it feels almost impenetrable when you’re using the finger test to see if the plant needs watering, it’s time to repot. Choose a well-draining indoor potting soil.
This is when to put your poinsettia in the dark
To recreate shorter days that will stimulate a poinsettia plant to change color, it needs 12 hours of complete darkness. Each night, put the plant in a dark room. That means no glow from night lights or outside street lights. Poinsettias need a period of absolute darkness for at least two weeks. One way to achieve this is to place your poinsettia in a dark closet or completely dark, unused basement room between 8 pm and 8 am every day. This should happen around mid to late September or early October.
If you don’t have a completely dark room, use a cardboard box. Make sure there aren’t any holes in it to let light through. And also make sure it’s big enough to cover the plant without disturbing the leaves. Just don’t forget to remove it in the morning. Any extra light during the dark period can interrupt the process and result in a completely green plant.
During the day, make sure your poinsettia gets lots of natural sunlight. This will help it develop lots of new healthy growth.
If you follow all these steps, you should have colorful leaves by around a mid-November timeframe.