Poinsettias are everywhere around the holidays. Their bright color make them perfectly festive for this time of year. Poinsettia (Euphorbia pulcherrima) became possibly the most popular of all holiday plants because of its mix of red bracts and green foliage. Let's explore some interesting facts about poinsettias.
The poinsettia is a member of the huge genus Euphorbia, commonly known as spurges. There are around 2,000 different species of plants in this group, and if you don't recognize the name, you would certainly recognize some of its members. The Pencil Cactus and Crown of Thorns are also both Euphorbias. From tiny little plants to gigantic trees, the genus actually has a lot of interesting varieties to enjoy.
History of the Poinsettia
Poinsettia (Euphorbia pulcherrima) is the plant we're talking about this month, though. One fateful day in 1828, Joel Roberts Poinsett, Mexico’s first United States Ambassador, found a bright red shrub by the side of the road. It was introduced to the US in the early 1800s by the American ambassador to Mexico, a Mr. Joel Poinsett, from whom it also got its common name. Impressed by the beauty and peculiarity of the plant, Poinsett brought cuttings from the roadside shrub back to his South Carolina greenhouse and the rest is history. Years later, horticulturist William Prescott was tasked with renaming the Euphorbia pulcherrima, as it had become quite a popular plant in the United States.
The poinsettia was described as a new species in 1834 by the German scientist Johann Friedrich Klotzsch. Klotzsch credited Carl Ludwig Willdenow with the species name "pulcherrima", and the authority is given as Willd. ex Klotzsch. Wild poinsettias occur from Mexico to southern Guatemala, growing on mid-elevation, Pacific-facing slopes. The Aztecs were the first to cultivate poinsettias. Cultivation in the US began when diplomat Joel Roberts Poinsett sent some of the plants back to his greenhouses in South Carolina in the 1820s.
Albert Ecke emigrated from Germany to Los Angeles in 1900, opening a dairy and orchard in the Eagle Rock area. He became intrigued by the plant and sold them from street stands. Until the 1990s, the Ecke family, who had moved their operation to Encinitas, California, in 1923, had a virtual monopoly on poinsettias owing to a technique that made their plants much more attractive.
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What is a Bract?
Like many other spurges, its beauty is found in its bracts rather than its blooms. So, what's a bract? It's a leaf-like structure on a plant, that looks like a leaf, but it is not. The "blooms" on a bougainvillea are, in fact, bracts. If you look at the center of the bracts, you will see the actual little blooms. Sunflowers and daisies grow bracts. If you look at the flower heads, you'll see the green leaf-like things around the blooms, and those are bracts. Bracts perform a variety of useful functions, but the most ornamental ones seem to be designed to attract pollinators with their striking colors.
The plant bears dark green dentate leaves that measure 6-16 centimetres (2.4-6.3 in) in length. The colored bracts-which are normally flaming red, with cultivars being orange, pale green, cream, pink, white, or marbled-are often mistaken for flower petals because of their groupings and colors, but are actually leaves. The colors of the bracts are created through photoperiodism, meaning that they require darkness (at least fourteen hours at a time for 6-8 weeks in a row) to change color.
Caring for Your Poinsettia
When selecting a poinsettia, there are a number of factors to consider. Choose a plant with thoroughly colored bracts and foliage from bract tip to end of the stem. Be sure that the plant is full on all sides and that the bracts and leaves are not drooping. A stiff stem will be fairly indicative of durability. Lastly, check the yellow flowers in the center of the poinsettias.
Now, when you bring your new poinsettia home with its healthy green leaves and bright red bracts, it may soon show some stress signs by yellowing a few of its leaves. Just pluck those leaves off and all will be well. Give it as much light as you can, and let the soil get somewhat dry before watering again. This is a tropical plant, and it doesn't like cold weather, so keep the plant warm. Poinsettias do best in night temperatures between 55° to 65°F and day temperatures between 65° to 70°F. Water the poinsettia thoroughly when the top of the soil dries out.
A traditional potting soil is suitable for poinsettias, but it is important that the soil be loose to allow for adequate draining. Water poinsettias only when the top 1-2 inches of the soil feels dry to the touch. It is important not to overwater. Like with many potted plants, watering poinsettias is a delicate balance. The soil should never completely dry out, but it should only be watered to the point of saturation. If the plant sits in standing water, it can fall victim to root rot.
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Enjoy the plant through Christmas time, and once you're on the other side of the season, it'll start to go dormant. This is the point when most people throw it out, but we're gardeners and we can't bear the thought of throwing away a live plant, so let's have some fun and keep growing it. Keep caring for it as usual, giving it plenty of light and watering as usual. As we get into springtime, slow down the watering and let it stay dry for longer periods of time. When the stems start to shrivel up a little bit, go ahead and cut the whole plant back to just a few inches, and store it somewhere cool.
Reblooming Your Poinsettia
The answer to this question is not a straightforward one. Technically, poinsettias are perennial, but they require some care in order to come back each year. The temperature of the environment is vital for the continued survival of a poinsettia. In warm climates, poinsettias may have no trouble coming back in full force each season. Starting in mid summer, take it out, submerge it in a bucket of water, wash off as much of the old soil as you can, and then repot it into the same container using nice fresh potting soil. Put it on your shady porch, water it, give it some nice fertilizer (I like vermicompost tea) and treat it like you would any other potted plant. As it grows, pinch the stems to encourage branching.
Now here's the interesting part. When you get to early October, you need to trick it into producing the colored bracts, and you do that by giving it alternating darkness and light. So at 5:00pm put it in an absolutely dark closet, and then at 8:00am bring it back out into the light. Do this each day, and the plant will soon think it's the time of year to "flower" and will start producing those snazzy red bracts. A gardener feels a great sense of accomplishment in forcing a poinsettia, and I recommend everyone do it at least once, if only for the fun experience.
At the beginning of October, the plant should be kept in complete darkness for 12-14 hours each night for a period of 8-10 weeks. This may require moving the poinsettia to a dark space, such as a closet, or covering it entirely with a box. The poinsettia also needs sunlight during the “reblooming” period. Move the poinsettia to a location at which it can receive 6-8 hours of indirect, but bright sunlight each day.
All poinsettias are short-day plants--that is to say, flower bud and bract formation can be initiated only by an eight-week period of no more than 10 hours of light and no less than 14 hours of total, uninterrupted darkness per day. In addition, the plants are treated with a hormone that reduces stem length. After about 8 weeks, bracts and flowers should start to form.
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After September, give the plant no less than 14 hours of total darkness per day for eight weeks (no easy task in most homes). The darkness must be uninterrupted each night or the buds will fail to form. To aid success, keep the night temperatures low and don't forget to expose the plant to light each day after the 14 hours of darkness. If it is difficult to avoid a light source at night, try completely covering the plant very gently with a black cloth or a large box from 6pm to 8am.
A gardener feels a great sense of accomplishment in forcing a poinsettia, and I recommend everyone do it at least once, if only for the fun experience.
Two ways of proceeding are then possible. You can take 3-inch-long tip cuttings from the new side shoots and root them to make new plants (see Propagation). If you choose to use the old plant instead of taking cuttings, replant the newly growing old plant in fresh soil-based potting mix. Do not use a larger pot than the original one.
Other Poinsettia Care Tips
Poinsettias can be planted outside, but they are very intolerant of frost. Because of this, you must bring poinsettias inside when temperatures drop below 50℉. The ideal temperature for poinsettias lies between 65 and 70℉, and they should be kept away from any cold or warm drafts.
Poinsettias should not be fertilized during the blooming period. In the spring, summer, and fall, they can be fertilized every 3-4 weeks with a half-strength fertilizer.
The best time to prune a poinsettia is in February or early March. When pruning, cut the stems back so that they remain 4-6 inches in length.
Poinsettias require bright but filtered sunlight each day. A south, east or west-facing window exposure will all work but ensure that the plant is close enough to the window to receive gentle light on its leaves.
Water early in the day and use tepid water. A relative humidity above 50% is preferred to successfully grow poinsettias and helps to keep the soil from drying too rapidly. That amount of air moisture can be difficult to achieve in a New York area home. Additional moisture can be provided by setting the plant on a tray of pebbles that is kept moist and/or using a humidifier.
Unless the plant is to be forced or grown from cuttings for future holidays, extra fertilization in unnecessary. Only when quite pot bound, move the plant into the next largest pot size. If the plant is in a plastic pot move it into a new plastic pot; if it is growing well in a clay pot move it into a new clay pot. Pots should always have a drain hole.
If your poinsettia is dropping its leaves, there may be a number of factors to blame. Poinsettias are intolerant of the cold, so if the temperature is too low, it may begin to lose leaves. Additionally, poor nutrition or insufficient light can be at fault. You might notice that the color of your poinsettia is not as vibrant as it once was.
Poinsettias can turn yellow for various reasons. In order to best diagnose the problem, look at the roots. If the roots appear healthy, the poinsettia is probably not getting enough water and/or light.
Propagation
Propagation of poinsettias is done with plant cuttings. Parent plants should be kept in bright, temperate locations in order to produce healthy stems that will work well for cuttings. When the desired cuttings are around 3-4 inches long with two or three leaves, they can be removed and used for propagation.
Tips of healthy side shoots that have not produced flower bracts make the best cuttings. These occur on plants that have finished flowering and then experienced a period of dormancy, in normal light but with minimal water. Make a 3 to 4" cutting just above a node, let it callus so that no more milky sap oozes and place it into a small pot containing a mixture of equal parts of peat moss and coarse sand or perlite. Keep it in filtered light and keep mix barely moist. Allow the top two-thirds to dry out between waterings.
Here's how to propagate poinsettias through stem cuttings:
- Prepare the Pot: Fill the small pot with the sterile potting mix.
- Select the Cutting: Choose a healthy stem that is at least 4-6 inches (10-15 cm) long and has at least two to three leaves.
- Prepare the Cutting: Remove the lower leaves, leaving at least one or two at the top.
- Provide Light: Place the pot in indirect light.
- Check for Root Growth: After 4-6 weeks, gently tug the cutting. If you feel resistance, roots have likely formed.
Are Poinsettias Poisonous?
Contrary to popular belief, poinsettias are not poisonous. After feeding rats “extraordinarily high doses of various portions of the poinsettias” scientists in an Ohio State University study found the rats to be unaffected. To put the “extraordinarily high doses” in perspective for humans, OSU associate professor Robert McMahon says a 50-pound child would have to eat approximately 500 poinsettia leaves. That being said, you probably shouldn’t go eating poinsettia leaves as a snack. Despite their horrible taste, they can cause nausea or vomiting, especially in dogs and cats.
The milky sap of the poinsettia has been known to cause skin irritation and rash, especially on those with latex allergies.
Table: Poinsettia Toxicity Facts
| Aspect | Details |
|---|---|
| Toxicity Level | Low |
| Symptoms | Nausea, vomiting, skin irritation |
| Risk to Pets | Mild drooling or vomiting, rarely diarrhea |
A survey of more than 20,000 calls to the American Association of Poison Control Centers from 1985-1992 related to poinsettia exposure showed no fatalities. In 92.4% of calls, there was no effect from exposure, and in 3.4% of calls there were minor effects, defined as "minimally bothersome".
If ingested, mild drooling or vomiting can occur, or rarely, diarrhea. In rare cases, exposure to the eye may result in eye irritation.
Poinsettia Diseases
Poinsettias are susceptible to several diseases, mostly fungal, but also bacterial and parasitic. Conditions that promote poinsettia propagation also favor certain diseases. Fungal diseases affecting greenhouse poinsettia operations include Pythium root rot, Rhizoctonia root and stem rot, black root rot, scab, powdery mildew, and Botrytis blight. Bacterial diseases include bacterial soft rot and bacterial canker, while a viral disease is Poinsettia mosaic virus.
Overwatering can lead to root rot.
Infection by poinsettia branch-inducing phytoplasma is actually desirable, as it keeps the plants shorter with more flowers.
