How to Grow and Care for Poinsettias
Poinsettia - Euphorbia pulcherrima
In the northern hemisphere, poinsettias have long been known as the traditional flower of Christmas, for the brilliant red coloring they produce at this time of the year. In fact, the flowers themselves are relatively insignificant, small yellow pods, with black stamens emerging from the center. The real color comes from the large modified leaves or bracts which surround them, and contrast dramatically with the plant's dark-green pointed leaves.
Euphorbias are a large genus of plants which includes more than 1,600 species of variable form, size, and habit of growth. Those species commonly grown as house plants may be soft-leaved shrubs, small trees or heavily spined succulents. One characteristic shared by all euphorbias is that the stems contain a milky sap or latex, which flows freely if the plant is cut or damaged, and in some species is poisonous, though not in the poinsettia.
Euphorbia pulcherrima (pulcherrima means 'most beautiful') is the descendant of a 10 ft (3 m) tall evergreen shrub that grows wild in Mexico, where it was discovered in 1834.
Until the late 1950s, poinsettias were very much specialists' plants that had a limited life in the home: the leaves would drop off almost as soon as the plant came into a dry atmosphere. However, through breeding and selection, growers in Scandinavia and California, developed more compact strains which were much less temperamental, less inclined to drop their leaves and, with minimal care, would keep their colored bracts for many weeks. Today, these varieties have been developed further and, in addition to the familiar red poinsettia, there are now varieties in a wide range of colors.
Buy poinsettias when they are in full color, avoiding those which are dropping their leaves. To ensure the bracts remain attractive for 2 months or even longer, keep poinsettias under the conditions described below for Proper care. Thereafter, most people discard the plant because it is very difficult to retain them from one season to the next.
In addition to using a growth retardant to keep the plants compact, commercial growers subject their plants to a strict regimen that is almost impossible to follow in the average home. Nevertheless, some amateur growers do try to keep poinsettias and bring them into flower again. This involves following the strict guidelines described below in After flowering, but the resultant plant will still be much taller than commercially produced poinsettias as the dwarfing chemical used by professional growers is rarely available for use by novices.
Proper care guide
Atmosphere: Poinsettias are fairly tolerant but they are at their best if they are kept in an area free from cold draughts and gas fumes.
Cleaning: Not necessary. Do not use leaf shine.
Feeding: Add liquid fertilizer to the water once a month while growing and flowering. Inadequate fertilization can cause the leaves to drop.
Humidity: Spray the leaves daily with a fine mist spray, using rain-water if possible.
Light: Poinsettias like a good, natural light position which includes some direct sunlight filtered through a translucent blind or curtain.
Temperature: Keep at normal room temperature when in color (not less that 55° F (12° C) and not more than 70° F (21° C)). They can tolerate cooler temperatures at other times.
Water: Water only when slightly drooping foliage indicates the need; the potting mixture should then be thoroughly saturated.
After flowering, cut the top growth down to 2 in (5 cm) from the base, dabbing the cut surface with cotton wool dipped in petroleum jelly if the sap runs. Decrease watering and allow the potting mixture to become almost - but never completely - dry. When growth stops, keep the dormant plant at normal room temperature, in bright filtered light for 3 months, then water heavily. The plant, still in its old pot, will soon begin to grow again.
When new shoots appear, re-pot the plant in fresh soil-based potting mixture and the same size pot. Do not be tempted to use a pot larger than the original one. Bigger pots encourage the rapid growth of lush foliage at the expense of the flowers and bracts, and the result is likely to be a huge plant which is unrecognisable as a poinsettia.
Once re-potted, care for the plant as previously described under Proper care (see above), and give it no less than 14 hours of complete uninterrupted darkness nightly.
As poinsettias are highly light sensitive, precautions should be taken to ensure that the dark cycle is never broken. The glare of a street light or light entering beneath a door is often sufficient to prevent buds from forming.
What goes wrong
Leaves turn yellow and curl, then fall.
Too hot, dry and dark.
Water and spray regularly. Feed regularly and keep in a light place.
Leaves shrivel and dry.
Move to fume-free room.
Whole plant droops.
Move to protected position.
Leaves distorted and sticky with green insects.
Spray with pyrethrum or a systemic insecticide.
Leaves marbled with silver.
Silver leaf virus.
No cure. Destroy plant.