Caring for poinsettias
By Tracey Payton Miller
OSU Extension Horticulture Educator
In college I had to help grow three greenhouses full of poinsettias to sell. They are intense. For those who purchase poinsettias for the holiday, they are not a plant you buy and forget. I'll give you some tips to keep your poinsettia going strong through the holidays.
Poinsettias are the American Christmas plant, though native to Mexico where they were known as the Christmas Eve flower. Joel Poinsett, the first U.S. Minister to Mexico and amateur botanist, introduced the plant to the nation. Being native to the far south, poinsettias naturally hate the cold. They grow outside during winter in Florida or California, but not Oklahoma. Poinsettias are very tender. During our sale we cautioned against leaving them in a cold car, and put the plants into paper sleeves for protection. Keep that in mind when you buy a poinsettia; get them home soon and keep them out of the cold and drafts. Poinsettias don't like temperatures below 55 degrees and above 70.
Poinsettias are showy and lend themselves well to holiday decor. Red and white colors are popular, but colors can be variations of white, red, pink, and orange. In addition, the bracts may be variegated or contorted into a rose-type shape. My favorite variety is Heirloom Pink, a pink poinsettia with off-white bract edges. A bract is a specialized leaf structure, where the color is manifested. On poinsettias, the true flowers are small and yellow, located in the center of the bracts.
Light is an important factor in the longevity of your poinsettia. Place the plants in areas that receive at least six to eight hours of natural or artificial light. Grouping poinsettias with other houseplants creates a humid, desirable micro-climate.
Watering is determined by the weight of the pot or the soil color. If the pot is heavy, or the soil dark, water isn't needed. If the soil is faded, and the pot is light, apply water. Flagging, or slight wilting, isn't harmful to the plant and is a good indicator on when to water. A turgid poinsettia leaf sits at a 90 degree angle. Flagging is wilting to the point around 45 degrees. I get the question "how do I know when to water?" a lot. In any situation, stick your finger in the soil. Gardening, even on the smallest scale, isn't a clean job. So get some soil under your fingernails. When watering, a small amount of water should leach out the bottom of the pot and drain. Don't keep your poinsettias (or most any other plant) constantly wet. Roots need air too.
Most cultivars hold their bracts for a very long time, giving you months of enjoyment before defoliation. Therefore, I recommend buying a new plant than try to keep a poinsettia through the year. However, I know some of you will want to try over-summering a poinsettia. Many poinsettias can be grown indoors as a foliage plant after the color is gone. Or you can plant your poinsettia outside. To do this, cut back the stems in March to 4 inches above the soil surface. In mid-May, plant the poinsettia in the pot, in a partly shaded area. Fertilize using a complete, pelleted fertilizer during the summer, and prune any roots outgrowing the container. Long shoots will form; prune these in mid-July and again in mid-August to induce branching. Move poinsettias indoors in late September. Poinsettias "color" in response to short days. To produce color, plants must be kept in complete darkness from 6 pm to 8 am each night, and placed in a sunny window during the day.
Contrary to popular belief, poinsettias are not poisonous. However, some may be allergic to the milky sap exuded when plant parts are broken (common in those plants belonging to the Euphoria family). Like many ornamental plants, poinsettias are purely used for their beauty, so enjoy them while you can.