Poinsettias can take cooler temps, save growers energy

WEST LAFAYETTE, Ind. (WLFI) - Growers who painstakingly choose their poinsettia cultivars can lower their greenhouse thermostats this October to save on energy costs – and produce high-quality plants.

It’s a new idea discovered by Purdue University and the University of New Hampshire in a recent study.

Associate professor of horticulture Roberto Lopez says poinsettia cultivars (varieties created and maintained with intention) that initiate and finish within six to eight weeks, are medium-to-high vigor, and have naturally large bracts, will do fine in cooler temperatures if flower producers want to save on heating costs.

The team’s findings showed red poinsettia cultivars that finish their growing process in cooler temperatures should just be planted a little earlier in the season to be ready for the holiday market.

"Over the past 10 years, energy prices for growers have increased more than 230 percent,” Lopez said. “As a result, many growers stopped growing poinsettias or lowered their thermostats without knowing what the cultivar-specific consequences would be.

"Now we know that they can save money by reducing finishing temperatures, but they have to plan ahead a little and work with the breeding companies to make sure they are using the correct cultivars."

Poinsettias are originally from tropical forests in Mexico and Central America, so U.S. growers need to heat greenhouses to roughly 75 degrees dayside and 67 degrees nightside in order to grow the crop in our climate.

Greenhouse technician Diane Camberato and Univ. of New Hampshire Extension specialist Brian Krug joined Lopez in testing temperatures.

They found the cooler the temperatures in a greenhouse, the longer it took for the poinsettias to reach maturity.

But other than that factor, the flowers were similar in size, color and other characteristics. Under the lower temperatures, the cultivars took from two days to three weeks longer to flower under the reduced temperatures.

In order to get the timing right, Lopez says growers need to start their poinsettias a week or two earlier in the month of August. This would possibly increase production costs, but if growers take advantage of warmer outside temperatures in August, it would offset the costs.

"Using these reduced finishing temperatures, a poinsettia grower could save a significant amount of money on energy costs," he said.

If you’ve already started poinsettias this year, you could potentially finish the plants in cooler greenhouses, assuming you are growing cultivars that can be cold-finished.

The Fred C. Gloeckner Foundation provided funding for the research.