One Last Poinsettia Push

We’re following up on James’ grower tech tip from last week because Nick Flax has had at least three calls with growers this week who desperately need to add some height to poinsettias to meet retail specs.

PROBLEM: There are only three weeks until Thanksgiving and that means poinsettias will start shipping soon! This time each year, we have conversations with growers whose poinsettias are not quite where they need to be size-wise and they are concerned their plants won’t hit retail spec.

Nick says: “While I am generally in agreement with my colleague James Doukas, who wrote a blog last week about not chasing finished spec, it’s not always possible to find different buyers for plants that are too small.”

NICK’S TIP: If your crop still needs to pick up a couple of inches, act now — but cautiously! Here are a few tips and tricks to get your points across the finish line:

The Cold Calculus First, consider your end goal before you start to push the crop. How much height do you need to make up and how much time do you actually have to do so?

• Use graphical tracking data to guide your decisions. If you haven’t implemented this process throughout the season (check out Nick’s past “Tech On Demand” newsletter tip HERE for details), measure at least five plants of each variety you feel are still too small to get a representative average height.

• Reserve the last week (at least) to tone the crop and avoid pushing plants right up until ship. You don’t want soft plants going into sleeves and heading to retail, as they will be much more likely to break!

Are you satisfied with the height of your plants, but you need bracts to be larger? Thankfully, you can do something about this!

Second, come to terms with a couple of things:

• If you are just 1 to 2 inches shy of spec, you may be able to reach the goal line with some purposeful environmental and crop cultural tweaks.

• If your crop is 3 or more inches shy of spec, it’s unlikely that pushing for additional size will end well. In this case, take James’ advice and have some frank discussions with your wholesale customers and find alternative sales avenues or other ways to fulfill orders if needed. If you are growing strictly for in-house retail sales, perhaps this year is the year of “compact” poinsettias! Bushy and colorful is better than soft, floppy and broken.

Gaining Height If you make the decision to try to reach that finished spec and your crop only needs to put on about 1 to 2 inches, you can likely make up most of the difference by marginally increasing your DIF (difference between day and nighttime temperature), running media slightly wetter, and giving them a gentle “nudge” with PGRs. Here’s some food for thought:

• Increasing feed rate significantly or switching to a high-phosphorus fertilizer formulation to push size is not a good idea — just don’t do it.

• When increasing DIF, to minimize the impact on your average daily temperature (which largely controls the rate of color change), increase your daytime temp setpoint and reduce your nighttime temps in similar magnitudes. That way, the average stays at or close to the same, and you aren’t suddenly running significantly higher or lower overall temps. Failure to do this could lead to faster or slower color change and cyathia development than desirable. Also, be sure not to drop nighttime temps suddenly to avoid stressing plants or running into dewpoint issues.

• When running soil moisture levels slightly higher than normal, mildly increased turgor (internal pressure of cells) can encourage a little bit of stretching without significantly increasing the risk of “crud.” That said, don’t allow the root zone to stay sopping wet for long periods, just water/feed slightly earlier than you normally would. Be sure to manage greenhouse humidity levels by venting as much as possible to further reduce risk of crud and

  Botrytis on bracts with that extra moisture around. Also, make sure you’ve applied a good root-zone fungicide recently before using this approach, or pathogens like Pythium could sneak up on you.

Heavy use of gibberellic acid (GA)-based plant growth regulators (PGRs) won’t do the trick and is generally unadvisable at this stage. The better route is to give plants a little “nudge” with GA and let the mild PGR effect work together with your other environmental and crop-culture adjustments. For GA-based PGRs, be sure to use ones that contain both GA4, GA+7 and benzyladenine (BA), like Fresco and Fascination. These forms of GA coupled with BA generally yield more consistent results in poinsettias than PGRs containing only GA3.

• Drench applications of Fresco (Fascination is not labeled for drench) will enhance growth a bit more evenly across the plant, whereas sprays have somewhat of a localized effect on growth enhancement closer to the spray application site.

• At this point, a single 1 to 2 ppm drench of Fresco or spray of Fresco/Fascination is about all I would suggest. As James wrote in his tech tip last week, chasing a certain spec too hard often does not yield good results.

• Consistent application volume across the crop is key, especially when your goal is to not overdo it. For drenches, apply 1 fl. oz. per inch of container diameter + 1 fl. oz. per additional ppp to each pot. For example, a 6-in. pot with 1 plant per pot (PPP) would need 7 fl. oz. (about 205 mL) and a 10-in. with 3 PPP would need 13 fl. oz. (385 mL) per pot. As a foliar spray, dialing-in a half gallon per 100 square feet of bench space spray volume target is a solid standby.

• If you don’t have experience using GA-based PGRs in poinsettias this late in the season, exercise caution!

If bract size enhancement is your goal and you don’t want much additional height on the crop, about 3 ppm (foliar application) of Fascination or Fresco 7 to 14 days before anthesis (when cyathia are showing pollen) will increase bract size.

• Keep in mind that late foliar application may impact plant height. Test a few rates on different cultivars before applying to your whole crop.

• Foliar applications of Fascination/Fresco can also deepen the color of darker-bract cultivars and brighten the bracts of white cultivars.

• Be aware of the risks associated with applying foliar sprays to poinsettias with mature bracts. Some growers experience increased Botrytis pressure after applying these late foliar sprays due to prolonged leaf wetness and high relative humidity in the crop canopy. Adjust environment controller setpoints to eliminate prolonged periods of high humidity (more than about 4 hours) or apply an appropriate fungicide ahead of time to minimize the risk of encountering disease pressure.