Poinsettia and Photoperiodism... what is it?

Published on September 10th 2018
With their beautiful and distinctive red bracts, Poinsettias (Euphorbia pulcherrima) are synonymous with Christmas.
But these delightful seasonal leaves often don't make it as far as Christmas, or they fade as soon as the festivities are over. Poinsettias are notoriously tricky to get right.
As you can see in the post above, Tom lovingly nursed his poinsettia through winter, spring and summer. His hard work has paid off with lots of lovely green leaves.
But why aren't they red?! If you want red leaves for Christmas, the preparation needs to start now. Because it all comes down to photoperiodism.
This sounds more complicated than it is. Photoperiodism is a term that describes a plant's visual response to day length and daylight hours. Poinsettias display photoperiodism by creating colourful red bracts around the small yellow flowers in response to winter's shorter days and lower light levels.
It might not sound very festive and cheery, but the best thing for a Poinsettia in autumn is to place it in a dark room during the day. That should cause photoperiodism to kick in and stimulate the transformation of those gorgeous red leaves.

How to prepare your Poinsettia at home

  • Start moving your Poinsettia into a darkened room on 1st October and continue for 8-10 weeks. Your plant will need 14 hours of complete darkness a day.
  • Each day, once your Poinsettia has had 14 hours of darkness, it will need 6-8 hours of strong sunlight.
  • Use a general liquid fertiliser to help your Poinsettia retain its vigour.
  • By the end of November, you should see a marked difference in your Poinsettia, with the red leaves really coming through.
Commercial growers do essentially the same thing, just on a bigger scale. They use blackout cloths, artificial lighting and growth regulators to ensure the Poinsettias on the shelves will be ready for Christmas. And they've got a lot of work to do, with over 4 million Poinsettias bought and sold in the UK every year!
The classic red Poinsettia is always by far the most popular, but pink and white varieties are available if you want something a little more unusual.

Remember to share your Poinsettia progress with us on the app!

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