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Poinsettias grow in a greenhouse at Gulf Coast Research and Education Center in Bradenton

A curfew for poinsettias!

Advent red variety poinsettia plants

Advent Red variety poinsettia plants (Euphorbia pulcherrima) growing in a University of Florida greenhouse. [CREDIT: UF/IFAS, Tyler Jones]

Let’s talk poinsettias: most people either love them or hate them – there is little middle ground. Many people love their cheery colors, while many others hate that the plants can be temperamental, dropping all  their leaves if given too much water.

When a flower is not a flower

That being said, the fascinating thing about the poinsettia is that those cheery red ‘flowers’ are not flowers. Rather, they are bracts.

A bract is a botanical term for colorful, modified, accessory leaves which surround flowers. The poinsettia’s true flowers are actually the tiny yellow  buds and petals hidden among the large red, white, or variegated bracts which make the plant a popular holiday decoration.

The bougainvillea is another common plant which is more popular for its bracts rather than its true flowers, which are the tiny cream-colored buds and petals at the center of the plant’s colorful bracts. But, I digress.

Lights out!

Poinsettias grow in a greenhouse at Gulf Coast Research and Education Center in Bradenton

Poinsettias grow in a greenhouse at Gulf Coast Research and Education Center in Bradenton. [CREDIT: UF/IFAS]

Another fascinating thing about poinsettias is that they must receive 12-14 hours of low-light/darkness every day, starting in late summer, or they won’t turn red!

This means that from summer onward, poinsettia growers gradually impose a daylight curfew on their plants by blanketing their grow-houses in black shade cloth. This process is called “flower initiation,” and it provides poinsettias with the required amount of daylight hours for their bracts to turn from the usual green to the many poinsettia colors available at the garden center.

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