Greenhouse growers cause poinsettias toAt first glance, these poinsettias may look like they have a leaf disease but are actually quite healthy. The spottiness of the leaves is because they are in the interim stage of a controlled leaf color-change, according to Texas AgriLife Extension Service experts. (Texas AgriLife Extension Service photo by Dr. Karl Steddom)
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After Texas growers take great pains to produce beautiful poinsettias, plants free of diseases and pests that could live for years, most consumers will take the plants home and kill them within a couple of weeks due to improper care, according to Texas AgriLife Extension Service experts.
"Poinsettias are not poisonous. That's an urban myth," said Dr. Karl Steddom, AgriLife Extension plant pathologist. "But from a poinsettia's viewpoint, most consumers are lethal. Consumers don't mean to kill the plants. They just don't know how to take care of them."
Each year, East Texas plant nurseries will produce several million poinsettias in 6-inch pots for the holiday season, according to Steddom.
"Color Spot Nurseries in Troup alone will market more than a million poinsettias this year," said Dr. Scott Ludwig, AgriLife Extension integrated plant management specialist. "And that's only one of many nurseries in Cherokee County."
Both Ludwig and Steddom, who are based at the Texas AgriLife Research and Extension Center at Overton, work closely with the ornamental plant growers in northeast Texas, whose sales total more than $500 million annually, they said.
East Texas growers may start work with holiday season poinsettias as early as June or as late as August, Ludwig said.
"It's complicated, as some may start with pre-rooted cuttings, others may purchase unrooted cuttings and root their own, and still others may grow their own poinsettia root stock plants and take cuttings from them to root," he said.
Because of labor costs and the need of dedicated facilities, the more common method is to start with cuttings which are usually imported. The cuttings usually come pre-rooted in "Oasis Cubes," a small block of foam similar to that used by floral designers to hold flower arrangements. The cubes are sterile and can be saturated with water, but drain well.
Keeping the growth medium as clean as possible is important, because poinsettias can be host to a multitude of plant diseases, including molds, foliar diseases, blights and root rot. None of the diseases are of any risk to human health, but they can reduce the attractiveness of the plant, Steddom said.
The cubes are planted into growth medium, most commonly in 6-inch pots. Again, to limit soil-borne diseases, clean potting soil is used.
Insects can be a problem, particularly whiteflies, but not if growers keep a close eye on their crop and take prophylactic measures, Ludwig said
Another growing demand involves "black-clothing." The time which poinsettias bloom is determined by daylight hours. Poinsettias are native to Mexico, where changes in daylight cause them to turn from green to bright red right before Christmas, Ludwig said.
"We say 'bloom' but that's actually a misnomer, because it's the leaves that change color, not the bloom," Ludwig said. "But in most of the U.S., growers have to cover their greenhouses in light opaque shrouding to cause the plants to change color in time for the holiday season."
Growers will typically black cloth in stages, timing the operation so that some poinsettias change color by November for Thanksgiving, then at other times for various shipping periods up to Christmas, Ludwig said.
Of all the plant diseases to which poinsettias are susceptible, pythium root rot is probably the most common, Steddom said.
"Every year, some producers have at least small losses to pythium root rot," Steddom said. "The pythium organism can be found everywhere, but it is encouraged by over-watering and poor drainage," Steddom said.
Proper watering methods are essential. And as the disease is water borne, so growers have to take precautions about the disease being transmitted from one pot to the other by drainage.
Pythium root rot is also the most common scourge of poinsettias in the home, Steddom said. The slick holiday paper wrapped around pots prevents drainage. On top of that, consumers are prone to over-watering the plants.
"If they want to keep their poinsettias alive, remove the wrapper as soon as possible," Steddom said. "And don't over-water. Simply stick your finger in the soil and if it feels damp, don't water it. If you let the pot sit in standing water for any length of time, you'll probably kill the plant."
Steddom said they can put the holiday wrapper back on after they let the pot drain.
"Except in South Texas, where poinsettias might survive in an outdoor landscape, to keep the plants alive, consumers are going to have to give them lots of light andkeep a close eye on soil moisture levels," Ludwig said.
Poinsettias can be made to re-bloom for the next Christmas season, but it's an arduous chore, Ludwig said.
The plants need about 14 hours of darkness alternated with 10 hours of bright light for eight to 10 weeks, he said. Even a few hours of too much light will scuttle the process. The temperature has to be regulated too.
"Most people will kill the plant trying to get it to re-bloom," Ludwig said. "Considering all the work that goes into commercially grown poinsettias and the low cost consumers pay for them, it's easier to just compost them and buy a new plant the next holiday season."