Poinsettia is part of the euphorbia family which includes spurge, crown of thorns and other milky sap plants. While they are native to Mexico and Central America the plants were introduced to the United States in 1825 by the first US ambassador to Mexico, Joel Poinsett.
At the Botanical Center, we have 23 varieties of Poinsettias and about 500 plants. Sparkle is the splatter designed one. Tapestry is a short variety with green and gold foliage.
In the wild, Poinsettias may grow to ten feet on one stalk. Growers pinch the stems of houseplants as they mature to induce branching. The goal is to obtain 6 to 8 branches each with an inflorescence. The bright colored leaves are called bracts and the "flower" or inflorescences is called a cyathium which is a central female flower lacking any petals and surrounded by male flowers reduced to a single stamen. This is enclosed in a cup-shaped ring of tiny incompletely fused bracts with one or more nectar glands on their sides.
Poinsettias are naturally pollinated by insects and produce flowers in response to day length called photoperiodism. The milky white sap, called “crud”, if released will stick to a leaf or bract and turn that spot brown.
Poinsettias should be watered when the soil feels dry to the touch, but it is imperative that flowers and leaves not get wet. Brown spots will result if the leaves and bracts are hit with water.
The plants at the Botanical Center were grown by Master Gardeners at the University of Rhode Island greenhouses. Starting in July 2014, Master Gardener volunteers worked 6 days a week to grow 1500 poinsettias, including 73 varieties. URI is a test site for poinsettia growers and it is the only Master Gardener volunteer program among the test sites.
Master Gardeners measure the growth, note reversions back to original plant, track irregularities, and report each day's maintenance procedures back to the breeders. White fly is battled with sticky traps and BT is used on fungus gnats. Keeping a very clean greenhouse is the first line of defense against insect infestation.
The widespread belief that poinsettias are poisonous is a misconception. There is ample scientific evidence demonstrating that poinsettias are safe. The primary information resource used by most poison control centers, states that a 50 pound child would have to ingest over 500 poinsettia bracts to surpass experimental doses. Please note, however, that individuals may experience an allergic skin reaction to the poinsettia sap.
Photos by Sue Dunn.