Poinsettias are quintessential Christmas plants and one of the most popular houseplants around the globe thanks to their bright bracts. They are often gifted during the festive season and most people grow them as an annual and then get rid of them in the new year.
It need not be that way though. Poinsettias are a perennial in their native habitat and do not need to be discarded after Christmas. They can be encouraged to bloom again year-after-year with only a few basic steps, which includes giving them a period of complete darkness.
Looking after a poinsettia and getting it to rebloom can be simple. If you do get a poinsettia for Christmas, then think long-term and do not be so quick to discard the plant. We hear tips from houseplant experts for when and how to treat poinsettias to get them to bloom again.
Do poinsettias need darkness?
Poinsettias are photoperiodic plants and their blooming is triggered by longer periods of darkness. Without changing the length of daylight they get, and providing them with this darkness, the plants will not produce any new colorful bracts.
‘Putting poinsettias in complete darkness is crucial for encouraging them to produce their signature red blooms,’ says Ash Read, founder of Indoor Plants. ‘This mimics the short days of winter and tricks the plant into bloom mode.’
If you want your best poinsettia to rebloom for Christmas, then it pays to understand when and how to give the plants that crucial darkness they require.
When do I put my poinsettia in the dark?
To get the Christmas plants to flower again for the following festive period, there are a few steps to complete before giving them the darkness treatment.
Once winter is over, reduce the level of watering the poinsettias get and then prune the stems back to 4-6 inches tall in late spring. It is recommended to repot the poinsettia into a larger container and continue to water and regularly fertilize the plant with a feed for houseplants every 3-4 weeks.
Come fall, it is the time to start the reblooming process. Kayla Gajdascz, the founder of Mental Houseplants, says ‘the dark treatment should begin in early October’. She adds: ‘This timing aligns with the natural decrease in daylight hours and helps simulate the plant's native environment.’
Ash Read claims starting the darkness treatment in October will ‘give adequate time’ for the flowers to be in full bloom by the festive period to take their place as part of your Christmas decorating ideas.
Kayla Gajdascz is the co-founder and president of Mental Houseplants, a company dedicated to spreading the positive impact that plants have on our mental health. One way that the company does this is by partnering with NAMI, the National Alliance on Mental Illness (the Massachusetts chapter), and donating a portion of every sale to them.
Ash Read is the founder of Indoor Plants. He had a career in professional gardening before turning to writing. Indoor Plants aims to make gardening accessible and enjoyable for all.
Miracle-Gro Indoor Plant Food can provide all your indoor plants with the nutrients they require to thrive. It can be applied directly to the soil or mixed with water and added to plants
How many hours of darkness do poinsettias need?
To get poinsettias to rebloom successfully, the trick is to give them a consistent cycle of light and darkness. It is crucial to give them no more than 10 hours of light a day and to keep the cycle of light and darkness consistent for 8-10 weeks.
Vladan Nikolic, House Plant Expert and founder of Mr Houseplant, says: ‘These colorful plants need at least 12 hours of complete darkness within every 24-hour cycle to form the flowers. Ideally, you should enclose them in a closet or cardboard box each evening from 5pm to 7am. ‘
Once the bracts start to show color, then the poinsettia can be brought back into normal light conditions. There is no need for the periods of darkness to continue and it can remain on a windowsill all the time along with your other indoor plants.
Vladan Nikolic is a houseplant expert with over 10 years of experience. He is the founder of the houseplant care blog Mr. Houseplant and is a social media influencer for houseplants with over 500,000 followers.
Tips for keeping a poinsettia in the dark
It is common for poinsettias to be kept in a closet, unused room, or a box as part of its darkness treatment. Maintaining the lack of light is crucial to getting the plants to rebloom. Check the light levels in any room you opt to use and make any adjustments required to ensure there is complete darkness.
‘If you opt for a cardboard box, use duct tape to close all the seams to prevent any light from entering the box, says Vladan Nikolic. ‘It’s vital to ensure complete and uninterrupted darkness, as any light the plants receive during the dark treatment will delay or prevent flowering. ‘
The poinsettia wants to be kept in a room with a temperature between 60-70°F and away from any temperature fluctuations caused by the likes of heaters, underfloor heating, or cold drafts.
Continue to keep the poinsettia moist, but not overwatered or waterlogged, during the darkness process. However, do not fertilize the poinsettia during the treatment or during the holiday period.
Do poinsettias need complete darkness?
Complete darkness is required to get poinsettias to successfully rebloom. Kayla Gajdascz, co-founder of Mental Houseplants, warns that ‘even brief exposure to light can delay or prevent flowering’ and it is vital to ensure there are no light leaks if you want to guarantee a poinsettia blooms for Christmas.
How long do poinsettias have to be in the dark to turn red?
A good darkness routine will see a poinsettia be in the dark for 12-14 hours a day for a period of 6-8 weeks. This consistent cycle of light and uninterrupted darkness should be more than sufficient to trigger blooming.
Maintaining the correct light levels is important for poinsettias throughout the year. Not giving them enough light is one of the main culprits for why poinsettia leaves turn yellow, with overwatering the other usual suspect that causes unhappy plants. You can check the moisture levels in soil using your fingers, or with a soil moisture meter, such as this one available at Amazon.
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Drew’s passion for gardening started with growing vegetables and salad in raised beds in a small urban terrace garden. He has gone on to work as a professional gardener in historic gardens across the UK and also specialise as a kitchen gardener growing vegetables, fruit, herbs, and cut flowers. That passion for growing extends to being an allotmenteer, garden blogger, and producing how-to gardening guides for websites. Drew was shortlisted in the New Talent of the Year award at the 2023 Garden Media Guild Awards.
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