Growing Tips for Poinsettias

P. Allen Hammer
How many times have I written about poinsettias? Sometimes I feel like a broken record, but the simple fact is, I try hard to write about topics that will have the most impact on reducing your greenhouse problems, and your shrink. So that brings me to this list of tips for the 2009 poinsettia season:
Light. Remove your greenhouse shade as soon as possible. Shading for poinsettias is to control greenhouse temperature, NOT to control the light reaching the poinsettia crop. Poinsettias grow best under high light.
Make sure all greenhouse photoperiod lighting as well as night security lights are off when you start short days. I still get calls in November about poinsettias that aren’t coloring, only to find that a string of lights has been coming on from 10 p.m. to 2 a.m. since September.

Fertility. Sample your root medium and get a lab analysis. And check the function of your injector by measuring the EC of the fertilizer solution at the end of the hose. That is a simple test that should be done once a week during the growing season. Also, monitor at least the root medium pH and EC on a weekly or biweekly schedule. Understand how the fertilizer you are using affects plant growth and plant quality.

Water. Watering is still one of the critical growing decisions in poinsettia production. I don’t like the terms “dry grower” or “wet grower” for poinsettias. I would much prefer “optimum grower,” providing water to the crop when needed. To me, the most important factor in developing a good root system in poinsettias is water management of the particular root medium you choose to use for your production. Determining when to water is often difficult without a lot of hands-on touching and feeling of the crop. I’m a proponent of using all the available tools of light accumulation and root medium sensors as aids in plant watering decisions.

PGRs. Decisions on height control have to be made before height is a problem. We don’t have any chemical to shrink too-tall plants, and we have few good choices that significantly increase height. You must know the characteristics of the cultivars you’re growing. Plant genetics, plant timing, greenhouse environment and growing techniques all affect your PGR decisions. You should use graphical tracking to help with height control decisions. Graphical tracking can be as simple as weekly marks on wooden stakes placed throughout the crop. Those height marks must, however, be compared weekly to your desired height so you can make changes in a timely fashion to obtain the desired height in November.

Review. Go back and read your poinsettia notes from past crops. Don’t rely on your memory to produce the crop. At the very first sign of a problem, ask questions and use the plant diagnostic labs around the country to help identify problems and offer solutions.

Every decision you make will be seen in the finished poinsettia in November, and as I’ve always told my students, those decisions are made multiple times a day during the entire poinsettia season.

grower idea of the month

Sim McMurry, head grower/director of production, and Mark Yelanich, director of research, Metrolina Greenhouses Inc, Huntersville, North Carolina, stand in the Metrolina trial garden where they’ve developed a large shade, full sun and container trial area. As we discussed during my visit, garden trialing of plants is always difficult. The approaches can vary, from the professional gardener approach down to the “plant-‘em-and-come-what-may” approach, with little garden care provided. The Metrolina trial garden is somewhere between those two extremes. Having the trial garden at the greenhouse also overcomes the too-common “once-a-year field-day” snapshot of plant performance. On-site observation is probably one of the most significant values of the Metrolina trial garden. And as Sim told me, “We don’t necessarily use the trial garden to eliminate plants, because we understand how subtle differences can affect a plant’s performance in one year. But we do use it to select superior-performing plants for the consumer.”—P.A.H.

P. Allen Hammer is a retired professor of floriculture at Purdue University, Lafayette, Indiana, and is now in product development and support for Dümmen USA.