By Dr. Claudio Pasian, Department of Horticulture and Crop Science
The Ohio State University
Are your poinsettias on “cruise control”? This is a dangerous time for poinsettias because owners and head growers can become complacent and forget some simple, basic but important cultural practices that contribute to a great poinsettia crop.
“Remember what you already know,” is easy to say. In reality, you are very busy, and like many of us, take care of the urgencies first, often neglecting the important. Reading this article should be like going to the doctor for an annual physical exam. You know what the doctor will tell you before going to the visit: stop smoking, eat healthy food, exercise, reduce stress, etc. Do you follow the doctor’s advice? Going to the doctor helps reinforce the importance of having a healthy lifestyle. Well, with growing plants, it is the same. It can be difficult to practice all that you know about growing poinsettias.
Do you know the idiosyncrasies of the poinsettia cultivars you are growing? Breeding companies provide a wide selection of cultivars (cultivated varieties) that allow growers to satisfy different sections of their market. Each cultivar is not only different in its looks but also have different cultural requirements. How familiar are you with those requirements? How familiar are your head grower and other key employees? In the same vein, do you have a good rapport with the person in charge of technical support in the company, which owns the genetics you are growing? It is never too late to establish good working relationship.
Scheduling. The multitude of poinsettia cultivars that growers have available nowadays is a blessing to satisfy a variety of customers, but it requires growers to follow different scheduling regimes. Not doing so may result in poor quality plants. When to stick, when to pot, when to pinch, when to start short days, and when to ship: a “one size fits all” approach does not work. You need to know the optimum treatment for each cultivar.
The beginning influences the end. The quality of your rooted or unrooted cuttings plays a big role in the quality of your final poinsettia crop. If you have stock plants, you are responsible for the quality of the cuttings. If you buy them, you have to select the company that will provide the high-quality cuttings you need. What to watch for and control when rooting cuttings: Rooting temperature (72-75°F); adequate mist on the leaves by adjusting it to weather conditions; adequate light levels (1200 – 1500 foot-candles); and watch for Botrytis, Pythium, Erwinia, and fungus gnats.
The 1-2-3 of poor roots. One of the keys for a high-quality crop is having good roots. A variety of factors influence the quality of the roots. Among them is 1) poor growing mix, with low air porosity that retains too much water. Compounding this factor is 2) poor irrigation management. By keeping the growing mix too wet we favor 3) Pythium. The spores of this pathogen require free water to swim and attack the roots. As mentioned above, starting the crop with poor quality rooted cuttings may result in a poor root system. If plants do not have a good root system by the middle of October, little can be done to improve it afterwards.
Temperatures. Almost all growers know to give their poinsettia plants the appropriate day and night temperatures. However, when was the last time that the temperature sensors in your operation were calibrated? Are sensors placed close to the plants? Are sensors protected from direct solar radiation? Like a car, instruments need maintenance and need to be used properly.
Fertility. Poinsettias are considered “heavy feeders.” Fertilizers should be applied at a rate of 150 to 250 ppm nitrogen (N). More than 75% of that N should be nitrate-N. When using the pour-through method, electrical conductivity (EC) should be between 2.25 and 3.75 mS/cm. Molybdenum (Mo) is a micronutrient required by all plants. Poinsettias require high levels of this nutrient unlike other plants that require very small amounts. Growers need to be sure the fertilizer they are using has the right amount of Mo in the formulation. When Mo deficiency occurs, a corrective action is required. Drenching with a solution of sodium molybdate or ammonium molybdate at 77 ppm (77 g sodium molybdate or 54 g ammonium molybdate per 100 gallons of water) should correct the problem.
Low levels of calcium (Ca) will favor stem breakage and cause bract burn. During cloudy, low light level days, calcium does not move in the right amounts into the leaves or bracts. The result will be “bract edge burn” later in the season. To avoid this problem, growers start using calcium nitrate as a fertilizer and spray bracts with calcium chloride at a rate of 200 – 400 ppm calcium with a spreader sticker.
Fertilizer Injector. Growers should calibrate their fertilizer injectors. They may need both calibration and replacement of some parts. As stated above, all equipment requires periodical maintenance. By the time the grower discovers that an injector is not working properly, it may be too late to achieve a quality poinsettia crop. Being proactive is very important.
Scout! Scout! Scout! Poinsettias are the ideal crop to prove that “Murphy’s Law” is real. So many things can go wrong with poinsettias. The only way for growers to be successful is to constantly scout the crop. Scout for insects and diseases. This includes looking with a magnifier if necessary at the sticky cards, leaves, stems, and the roots of the plants by removing the pots.
Pythium. This is a very common problem for poinsettias. Growers need to apply (drench) a fungicide as a preventative and periodically check the roots. If symptoms of Pythium are present, more treatments are required. It is common that plants with roots severely infested with Pythium look “normal” (above ground) in the greenhouse. However, when these plants are moved out of the greenhouse to a more stressful environment, they immediately wilt because they do not have a functional root system to uptake water.
Pests and diseases. Several pest and diseases can affect poinsettia crops. That topic is beyond the scope of this article; however, if you experience any problems, please feel free to contact The Ohio State University plant pathologist, Dr. Francesca Hand, at firstname.lastname@example.org and our entomologist, Dr. Luis Cañas, at canas.4@osu,edu.
Take home message. Hopefully, after reading this article, poinsettia growers will realize that there is no such thing as a poinsettia crop on “cruise control.” Too many things can go wrong. Detecting problems before they become advanced is the formula for success. So, start scouting, follow it by more scouting, and then scout even more…