The Poinsettia (Part II)
Anatomy of a Poinsettia
In Mexico and Central America, the poinsettia grows best in shady places. In this zone, the plant may grow into a small shrubs or trees which can grow anywhere from about two to sixteen feet tall. In Mexico the poinsettia is a perennial shrub that will grow 10-15 feet tall.iv In the U.S., poinsettias are fascinating winter blooming plants that are primarily adapted to zones 8-11 with zone 8 being marginal and is best suited as an indoor plant. Louisiana is in zones 8 and 9.
The plant has dark green leaves which are about three to six inches in length which adds to the festive appearance of this plant.
When we look at the beautiful colors of the poinsettia, our instincts tell us it’s a beautiful flower, when in fact, what we are attracted to the beautiful colored modified leaves called bracts. The poinsettia is a short-day plant, monoecious plant, by which the plant has both female and male organs.
If we look closely, we will notice greenish yellow bulbs that we notice in the middle of the Poinsettia. These are called cyathia. The cyathia is an inflorescence that crams the male and female flowers together within the same structure. We call this whole unit the cyanthium, a structures that is unique to the genus Euphorbia, of which the Poinsettia is one. The cyanthium consist of one extremely reduced female flower standing in the center at the base of the involucre, consisting of an ovary on a short stem with pistil, and surrounded by five groups of extremely reduced male flowers, which each consist of a single anther on a stem.
When the plant sheds it pollen, the plant will drop its bracts followed by its leaves. For the longest-lasting Poinsettias, choose plants with little or no yellow pollen showing.
To the Home
In transporting the poinsettia from the retailer to your home, be sure the plant is well sleeved or wrapped when you take it outside on your trip home because exposure to low temperatures for even a short time can injure leaves and bracts. The plant is also quite brittle and subject to breakage and sleeving is highly recommended. Sleeving is when the plant is placed in a plastic or paper cone-type sleeve for protection. Once a location of the plant is selected, simply and gently tears or cut away the sleeve.
Placement in the Home
To extend the life and beauty of the plant, the best placement for the poinsettia is near a sunny window or some other well-lighted areas. Placement in a well-lighted area of the house will maintain good bract color and avoid leaf drop. Please make note that the placement of the plant in direct sunlight will increases the water demands of the plant. Make sure that the leaves don’t touch the cold window panes or damage will result.viii With proper care, the poinsettia will remain beautiful in the home for 2 to 3 months.
Remember, as beautiful as they are, we sometimes use the poinsettia as a welcome plant at the front door, but remember, poinsettias are not frost-tolerant. Poinsettias will grow successfully outdoors in temperate coastal climates, such as Southern California and Florida area, but if you wish to keep the poinsettias in Louisiana for an extended period, protective measures may be necessary. Planting is always recommended on the south side of house or other protective structures. As a general rule, the best potted plants for establishing in the landscape are ones that have been in good light while indoors and have remained green
and healthy. Make sure to choose a sunny spot that will not receive any artificial light at night. The varieties that have been found to do the best for outside are the red varieties.
Poinsettias are usually grown at temperatures between 60ºF and 70ºF in greenhouses, so this temperature range is recommended in home settings for long plant life not to exceed 75ºF. Excessive temperatures over 75°F will cause premature bract fading and leaf drop. If there are excessive high temperatures, this will shorten the plants life. Try to place them away from radiators, air moving objects such as registers, fans as well as open windows or doors. Place your poinsettia in a cooler room at night (55 to 60ºF) to extend the blooming time.
To aid in maintaining bract color, lowering the night temperatures to 60° to 65°F will help. On the other hand, to avoid chilling injury, avoid temperatures below 55°F.
If the plants are used outside, the wind and sun will have an effect on the soil moisture. In this case, watering is another key to the plants longevity. Monitoring the moisture is important, so as a rule of thumb is, use your thumb as an indicator to monitor. Feeling the soil is a sure way of determining if the plant needs to be watered or not. The top layer of the soil is the first to dry out. The planting medium should be slightly wet, with exception of the time being watered and not continuously soggy.
Another indicator is if the plant is continuously falling over. In this case, the soil is light because of no moisture and the top of the plant is too heavy. In this case, the plant needs water immediately. Make sure to examine the soil daily and water when needed. The best method of watering the plant is to place the plant in the sink and gently add enough water to soak the soil, allowing the excess to completely finish dripping through.
If you don’t water enough, the plant will wilt and cause premature leaf drop. If you water too much the lower leaves will yellow and then drop. The most common reason that poinsettias fail to last is because of drought. Remember, tomorrow is another day, check the moisture again.
Fertilizing your Poinsettia
If you keep your plant for over 30 days or even several months, apply a soluble houseplant fertilizer, once or twice a month according to the manufacturers’ recommendations. If the pot is covered with decorative foil, make sure to punch a few holes in the bottom of the pot for drainage. If the plants are used inside your home, make sure to place the plant in a saucer to catch any water run-off.
The economic impact of poinsettias sales in the U.S. is significant. Nationally, poinsettias are primarily sold within a six-eight week period going into the Christmas Season. With the poinsettia being the bestselling potted plant in the U.S and Canada, on an average, the poinsettia sales generate an average of $250 million/year in sales in the U.S. retail market with California being the top producing state.ix
Despite myths of claim that poinsettias are poisonous, they are not. A study at Ohio State University showed that a 50-pound child would have to eat more than 500 leaves to have any harmful effect this. In addition, the sap that exudes from a broken branch may cause temporary blindness if it comes in contact with the eyes. The worst that most likely will occur is that it will have an awful taste and although not poisonous, the result could lead to upset stomach, diarrhea and vomiting.
Magnesium Deficiency – Magnesium deficiency is a common problem with poinsettias. The symptoms are scorching on the margins and tips of the leaves and yellowing between the leaf veins. It is difficult to correct on affected leaves but can be prevented in subsequent years by applying magnesium sulfate (Epsom salts) in February/March and June/July)
Insects and Mites – Pests that attack poinsettias include aphids, mealybugs, soft scales, whiteflies and spider mites. The poinsettia hornworm is a particularly serious problem, since it can rapidly defoliate an entire plant. If only a few are responsible for the damage, pick off and destroy them individually rather than spraying the entire shrub.
Diseases – Poinsettia scab (Sphaceloma poinsettiae) is a fungal disease that causes circular, cream-colored spots on the midribs and veins of leaves and raised, often elongated lesions on stems and leaf petioles. Scab is most prevalent in the summer, and scab-infected branches should be pruned and discarded as soon as they are noted. Plants growing in poorly drained or over-watered areas are often
Author: Brent Jeansonne
LSU AgCenter, Baton Rouge, LA – Horticulturist – Northwest Region