Monitor plants for signs of insect damage, uneven watering and physical damage throughout the growing stages. Photo by Sally Colby

by Sally Colby

Growers who devote growing space to poinsettias have a considerable investment in personnel and labor until the crop is finished.

“A poinsettia can look great and have wonderful color,” said James Doukas, Selecta Ball Flora, “but unless it rings at the register, it isn’t useful to us as growers because we’re in this business to make money.”

Doukas acknowledged the fact that growers are just coming out of a busy spring season when it’s time to start poinsettias, but said good sanitation protocol will save headaches. “I see thrip infestations going from mums or annuals that are left near poinsettias either after they’ve been propagated or right after they’ve been moved out of a propagation zone,” he said. “If there’s some sort of physical barrier or they’re in a different zone, we don’t see thrips attacking poinsettias unless they’re already on a crop adjacent to the poinsettia crop.”

Propagation sanitation includes disinfecting or cleaning all surfaces in all areas where cuttings are handled. Workers should practice good hand sanitation and use foot baths when entering the propagation area. Disinfect all surfaces in the propagation house including benches, floors and ceilings. Doukas suggested using quaternary ammonium-based disinfectants, peroxide, chlorine dioxide or another oxidizing agent. Create a written sanitation protocol and be sure all employees are familiar with disinfection practices.

Environmental management for propagation includes shading the greenhouse to lower light levels to less than 2,000 fc. Soil temperature should be maintained at 68º to 72º and air temperature at 65º to 80º. Maintain high relative humidity of greater than 90%, especially for the first four to five days. Keep concrete floors wet to help maintain humidity and minimize air movement, but vent as needed to keep temperatures below 85º. Start to pull back on mist at around day five to seven (as cuttings start to callus) and begin night and early morning misting.

“Try not to overmist,” said Doukas. “The easy thing is ‘more water is better,’ but if you make it [the callus] too happy in a mist and too happy in a wet media, the callus becomes lazy and doesn’t throw a root out very well.”

Minimize water pooling on leaves. If overhead misters are used, cycle them on for the shortest time possible. Boom sprayers should balance the speed with moisture needs on the leaf surface. For more efficient mist, use a foliar wetting agent.

Fertility is critical for young plants. Once the callus is growing, it’s time to begin a fertility program. At stage one, Doukas recommends low phosphorus. Heavy leaching from propagation equals little or no media electrical conductivity (EC) at the time of initiation, but EC can be built up by day five to seven. Foliar fertilization can help, but it’s mostly to provide EC to the soil and for root initiation. Doukas recommended using 50 ppm nitrogen with low or no phosphorus fertilizer.

Doukas said when he visits poinsettia growers, he often sees distorted leaf tips from phosphorus drying on leaves. “If you’re doing overhead applications later in the crop cycle, you’re going to see that damage,” he said. “We’re eventually going to pinch that out. It might delay when we can actually pinch because we have to unfold the number of leaves to get the proper number of nodes before pinching. Try to avoid that – any time we’re applying overhead fertilizer with any amount of phosphorus, rinse with clear water. That means making sure the lines are discharged because ferilizer will still be in the lines. Be cognizant of the use of phosphorus overhead when growing tips of poinsettias, and at the same time, don’t overcorrect and overapply phosphorus.”

Initial insect control involves managing fungus gnat larvae. “Make sure you have a plan to control that population,” said Doukas. “Make sure you aren’t reinfecting new material as it’s coming in.” Cultural controls should be the first line of defense, along with an algae-free propagation zone, sticky cards for monitoring and properly managed moisture.

After the initial growing phase, plants won’t thrive in the propagation environment. “Apply a higher rate of fertilizer, possibly a tank mix of B9 cycocel, to stack the internodes prior to pinch,” he said. “Continue to monitor for fungus gnats.” With good culture going into transplant, plants will be ready to plant on day 23 to 28.

Growers can increase light levels and decrease temperature and humidity then. Doukas said growers who use high tunnels keep shade on all the way to October. “If you have vertical space in the greenhouse, you can increase light levels dramatically once you get out of propagation,” he said. “This is a southern plant, indigenous to Mexico. It isn’t going to get sunburned.”

Doukas compared hardening poinsettias to the process of acclimating popular tropical plants after they’ve been shaded. For plants raised in a double poly house, shade will help control the temperature. “It isn’t that the poinsettia can’t take a higher light level,” said Doukas. “It’s that the higher temperature inhibits it.”

Growers should watch for Pythium, Botrytis and Rhizoctonia. “These are not only propagation diseases,” said Doukas. “They’ll follow you to the later growing-on stage and bract development.”

The finishing environment is cooler with higher humidity. September brings higher humidity, but regulating humidity in October and November is critical. Doukas suggested focusing on getting humidity out of the crop in September to avoid disease. Some low nighttime temperatures are suitable, with daytime temps of 61º to 72º. At this point, irrigation should be drip. High temperature challenges can be difficult to deal with and should be monitored.

When using plant growth regulators for selected varieties, Doukas said an application of PGR (cycocel) in late propagation and after transplant will reduce internode length, which contributes to even branching. Pinch plants about 12 to 14 days after transplant and they’re rooting out into pots. Plants need not be rooted out fully to the pot edge, just actively growing roots and tips. Pinch to leaf count based on finished specs (six to seven leaves) after the pinch to produce a plant with six primary bracts. “Don’t leave too many leaves,” said Doukas. “That’s the storage of all the nutrition. This can result in wide plants and smaller bracts.”

The growing environment just prior and through two weeks after the pinch is most critical. High humidity is necessary to develop even branching. Misting, quick boom passes and wetting floors help achieve a higher humidity environment.

“Focus on building a foundation, staying in the middle of the road and not too wet or too dry,” said Doukas. “Now that the plant is established, we don’t want to run an excessive wet/dry cycle. If the media is too dry, EC will spike and lead to root injury and that’s the entryway for Pythium. If there are fungus gnats, they’ll chew on the roots and further vector the disease.”