Prized for their bright, showy flower bracts, poinsettias (Euphorbia pulcherrima) are a common sight in many homes during the holiday seasons. They are typically treated as annual houseplants, but are actually deciduous tropical shrubs that thrive outdoors within U.S. Department of Agriculture plant hardiness zones 9 to 11. Poinsettias require moderate to high levels of care year-round to ensure their health and continued blooming. However, their cheery appearance makes it worthwhile for many gardeners.
As a tropical plant, poinsettias are adapted to consistent levels of soil moisture during the active growing season. However, too much moisture can contribute to root diseases and leaf loss even in healthy plants. Water deeply but infrequently, allowing the soil to dry out on the surface between waterings. When irrigating container-grown plants, add water until it trickles from the drainage holes at the base. Poinsettias growing outdoors need a 2- to 3-inch layer of mulch around their base from the trunk to the tips of the outer leaves to conserve soil moisture and shield the roots.
Poinsettias grow quickly and most need supplemental nutrients to keep them from looking spindly and thin. Feed poinsettias biweekly from spring until early autumn. Fertilize with general purpose, 15-15-15 ratio fertilizer during the first half of the growing season to encourage root and foliage growth, then switch to a blooming fertilizer with an N-P-K number of 7-9-5 in late summer and early autumn to prepare them for their winter blooming period. Dissolve 1/2 teaspoon of fertilizer in 1 gallon of water and replace one watering every two weeks with the solution. Withhold fertilizer starting in late autumn to allow the plant a brief dormant period before blooming, then resume feeding in spring after the flowers fade.
Pruning and Grooming
Pruning is key to keeping poinsettias looking healthy and attractive. However, it must be timed properly to prevent damage to the plant. Prune poinsettias in spring after the flowers have faded. Cut back the entire plant to roughly 8 inches to encourage bushier foliage and stem growth later on. Trim off any unsightly stem growth or any dead or damaged foliage as it appears until mid- to late summer. Stop all pruning in late summer around mid-August because next year's flower buds will be forming. Before pruning, soak the shears for at least five minutes in full-strength household disinfectant cleaner, then rinse them in clean water to remove any pathogens.
Serious insect infestation rarely occurs in established poinsettias, although they may occasionally attract minor colonies of whiteflies and other pests. Discolored or dropped foliage is the most common sign of an infestation, although there may also be visible insects on the undersides of the leaves. Treat insect problems with a 2-percent insecticidal soap solution. Dissolve 4 teaspoons of insecticidal soap in 1 quart of water inside a spray bottle. Saturate the leaves -- top and bottom -- with the solution every four days. Rinse the leaves with fresh water a few hours after each treatment to prevent damage.
Poinsettias are short-day plants, meaning they require a long, dark night during their dormant period to ensure good color production in winter. Compelling poinsettias to bloom after their first year takes effort, but it is possible. However, the resulting bracts may not be as spectacular as during their first year. Starting in mid-autumn, place the plants in total darkness for 14 hours each night and expose them to extremely bright, diffuse light for six to eight hours each day. The flowers will begin to appear in eight to 10 weeks. Texas A&M Extension advises that you should make sure that poinsettias kept outdoors should get only natural sunlight, because added light from yard or street lights discourages blooming.