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You Can Grow It: Poinsettias for the holiday season

The poinsettia's color change is triggered by the length of daylight, just like outdoor trees and shrubs.

BOISE, Idaho — Poinsettias don't grow wild in Idaho, or even in landscaped yards and gardens.  But one look at these brightly colored blossoms, and you know it's the holiday season.  

Poinsettias are an iconic symbol of Christmas. But have you ever wondered where they come from, and how they get from a green plant to these colorful beauties?  

Poinsettias are native to Mexico, and were unknown in the U.S until 1828, when an American named Joel Poinsett, a botanist who was serving as the U.S. Ambassador to Mexico ran across them growing wild. There, they were known as the 'flor de nochabuena', or the Christmas Eve flower.  Poinsett sent samples back to the u.S., where they soon became known as poinsettias in his honor.

Poinsettias thrive outdoors in warmer climates, even in some parts of America, including Hawaii, Florida, and parts of the southwest. They can grow into large shrubs up to 15 feet high.  But while Idaho's climate is too cold for poinsettias to grow outdoors year-round, inside Edwards Greenhouse in Boise, conditions are ideal.

Starting in June, poinsettia cuttings called plugs are set out in the greenhouse to be watered and fertilized. They'll continue to grow to various sizes, depending on the size of their containers.  

The poinsettia's color change is triggered by the length of daylight, just like outdoor trees and shrubs. The plants need about 14 hours of continuous darkness to initiate their color change.  

So for weeks the plants stay green. But around late October, a subtle change begins to occur, with a hint of red showing up in the leaves.  By mid-November, the full change is underway, and all of the various colors and patterns have begun to emerge.  

What we think of as flowers, the part that changes color, are actually colored leaves called bracts.  The plants continue to grow more brilliant each day, until they're ready for you to enjoy in your holiday displays. 

Poinsettias come in nearly 100 different colors, shades, and shapes. At Edwards there are nearly three dozen varieties, including 10 to 15 different shades of red, as well as pink, white, mauve, salmon, and yellow shades.  There are even some mottled and variegated varieties known as novelties.

Classic red is the most popular, and are used in the beautiful annual Capitol poinsettia tree in the center of the Idaho State Capitol rotunda, atradition for nearly 40 years.

The colorful transformation of the poinsettia is truly magical, making it an iconic symbol of a magical time of year.

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