Experience continues to confirm the energy-saving benefits of cold growing. Syngenta Flowers’ research reveals more specific results and how this technique could be viable for your operation.
In recent years, growing poinsettias at cooler temperatures has gained momentum with many North American growers who have successfully adopted the technique. The general idea is to use the natural warm temperatures in August and September to build plants’ foundation, then drop temperatures in October and November to save energy after bracts begin to color. The topic has stimulated research at both the university level and with suppliers; new information is generated every year, and researchers are gaining a better understanding of when to drop to cold temperatures and which varieties adapt best to this type of production.
While plants look different under cool finishing temperatures compared to those grown warm (above 65° F average daily temperature), there appear to be several benefits to growing poinsettias under cooler temperatures.
If you were to ask growers why they should grow cold, the most obvious answer would be to save energy and fuel. We know that energy can be saved when early-season varieties with shorter response times are grown cooler in October and November (versus growing varieties with longer response times, at traditionally warm temperatures). In this case, these early-season varieties are sold one to two weeks later than normal as mid-season varieties. There is definitely a place for some great early-season varieties to fit into this system. Current research at the university level is examining the calculation of degree-days and other models to better predict temperature inputs and potential fuel savings when growing under cooler temperatures.
Because cooler temperatures delay flowering, growing varieties with relatively long response times is generally not recommended because production times would be extremely long (using significant fuel and energy) and key sales dates could be missed. Growers should work with suppliers on which varieties are best suited for cooler temperature regimes.
Besides energy savings, growing poinsettias cooler also results in less chemical growth regulator (PGR) and insecticide use. Poinsettias just don’t grow as fast or as tall under cooler temperatures, so less PGR is needed throughout production. Cooler temperatures also slow down metabolism and reproductive rates of three major insects that can attack poinsettias: whiteflies, thrips and mites. While plants still need to be scouted regularly, cold growing can potentially reduce insecticide spray frequency.
If you’ve ever seen poinsettias produced under these cool temperatures, you’ll notice tighter bracts and thicker, more compact stems. The result is tougher plants that withstand the rigors of sleeving and shipping better than plants produced at warmer temperatures. Also, bract color intensifies, especially for red, pink and marble varieties. (Whites become creamier, which might be undesirable.) While bracts are smaller under cool growing temperatures, the tradeoff in improved shipability and bract color justifies it for many varieties. Some debate still exists as to whether cool-grown plants hold up better in the post-harvest interior environment (e.g., reduced cyathia drop, bottom-leaf yellowing, bract-edge burn). Further research is needed in this area.
With all the talk of going green and taking more sustainable approaches to agriculture, growing poinsettias cooler is certainly a move in the right direction. Growers who use cold-growing techniques should promote their poinsettias as such. Both wholesale and retail producers should note fuel savings and reduced chemical usage in whatever way they can. Signage, radio and TV ads, and newspaper articles should all be used to promote more environmentally friendly poinsettia production. We see it more these days with food and consumer products, so we should be doing the same with poinsettias. It might be the shot in the arm the industry is looking for in poinsettia sales.
Syngenta Flowers’ Research
As mentioned earlier, there has been significant recent research on producing poinsettias at cooler temperatures. At Syngenta Flowers, we have conducted trials to determine which Syngenta varieties are best suited for energy-efficient production.
In one greenhouse study, two different temperature regimes were tested (62° F ADT and 65° F ADT) with plants introduced to these cool growing conditions over several different dates beginning Oct. 5. Results were compared with plants grown at a constant 70° F ADT, which would be more of a traditional approach. Plants were grown in 61/2-inch pots, then transplanted on either July 18 (compact varieties) or Aug. 1 (medium to vigorous varieties). Day and night temperatures varied within each temperature regime, but average daily temperature remained consistent for each respective regime. Once treatments began, the idea was to let the greenhouse warm up moderately during the day (using the natural radiation from the sun) and then drop temperatures during the night to maintain our respective average daily temperatures. We tried to make sure that night temperatures did not go below 55° F. Data was collected on bract development, flower timing, plant appearance, height development and post-harvest quality.
Based on results from this and other studies, we found that several Syngenta varieties perform well under cooler growing temperatures. Our very best varieties were ‘Early Orion Red’ and ‘Orion Red’. Both are early-season varieties with good vigor and bract size. Other varieties that did well were ‘Mira Red’, ‘Mira White’ and ‘Improved Cortez Red’, which replaces last year’s ‘Cortez Red’. Mira varieties are new early-season varieties with moderate vigor, while ‘Cortez Red’ has been improved to make it several days earlier and sturdier than the old Cortez. ‘Dark Red Carousel’, a mid-season novelty variety, also did well under cool-growing conditions. While it was later and more compact, its small, curly bracts are not affected by cooler temperatures as much as other varieties. Results may vary depending on different climates and greenhouse conditions, but we can provide examples of guidelines and information in producing Syngenta poinsettias under cooler temperatures.
For a chart that shows bract development for ‘Early Orion Red’ over time for the 62° F and 65° F treatments starting on Oct. 5 and Oct. 17, visit the Cultural Information and Diagnostics page at www.syngentaflowersinc.com . As expected, in this situation, the later plants are introduced to cold-growing conditions, the larger the finished bract size and less delay in finish. The tradeoff for larger bract size and faster finishing is additional fuel consumption. Recent research gives some indication that gibberellic acid sprays may be used several weeks before maturity to help improve final bract size on plants grown under very cool temperatures.
In our trial, ‘Orion Red’ behaved similarly to ‘Early Orion Red’ but was just a few days later to flower. As mentioned earlier, our experience shows these two varieties are good choices for cool finish (either 62° F ADT or 65° F ADT) beginning early to mid-October. Overall plant height and bract size were not as affected with these two varieties as with others we tested.
While ‘Early Orion Red’ and ‘Orion Red’ can be grown cool beginning in early October, introducing plants to cold treatments later results in more predictable crops. This is especially true for Mira varieties, ‘Improved Cortez Red’ and ‘Carousel Dark Red’. Plants have slightly larger bracts and a moderately taller finish size when cold treatments start later in October. Plants can be grown in 62° F ADT or 65° F ADT beginning Oct. 17 and have good finish quality.
All plants grown under cooler temperatures have more intense red bract color, especially those at 62° F ADT. Plants grown under cooler temperatures also have thicker branches and tighter plant habits. Cool finishing helps use ‘Early Orion Red’ and ‘Orion Red’ as mid-season reds with improved plant strength and bract color.
Figure 1 (page 19) shows a simple bar chart of when ‘Early Orion Red’ plants became saleable (subjective evaluation based on overall color and saleability). Plants grown under cool temperatures show delay in bract development, so the introduction date should be considered. Plants introduced to 62° F ADT on either Oct. 5 or Oct. 19 have the longest finish times. Plants introduced to 65° F ADT on either Oct. 5 or Oct. 19 were significantly less affected than those at 62° F. Depending on the variety, plants introduced to 65° F ADT were generally three to 10 days later in finish than the warm control (70° F ADT). Flowering information and tools to help growers predict finishing times under various temperatures and introduction dates are available at www.syngenta  flowersinc.com.
Figure 2 shows height curves for ‘Early Orion Red’ under different temperatures and introduction dates. ‘Orion Red’ shows very similar results. Other recommended varieties, such as ‘Mira Red’, ‘Mira White’ (Figure 3) and ‘Improved Cortez Red’, had slightly larger gaps between the curves, indicating that cool temperatures had more of an effect on height reduction. Growers should use these trial results as an estimate to predict finish height. Generally, the longer the plants are exposed to cold growing conditions, the shorter the finished plant height. Growers should be proactive and go into the cold-growing regime with adequately sized plants.
More to Think About
Additional considerations for cold growing poinsettias: