Christmas in July? Not quite, but poinsettias are making their way into greenhouses across Ontario, and they always arrive at the hottest time of the year. Nutritional issues, environmental stress and PGR mistakes can all be costly in this high-value crop. Read on for production tips and how to manage this seasonal favourite in the greenhouse.
Only looking for certain information? Choose from the list below:
Nutrition
Poinsettia are picky eaters – the conditions need to be right for them to uptake fertilizer and avoid deficiencies. Maintaining a pH of 5.5 – 6.5 in the media and using fertilizer with a nitrogen concentration of 150 – 300 ppm will help you avoid most nutritional disorders.
It’s essential to start feeding early, about 10 days after sticking, to prevent lower leaf yellowing (nutrient deficiency) and to produce larger leaves at the bottom of the plant. Remember, the goal is to have a pyramid-shaped plant with large leaves on the bottom to create the appearance of fullness.
Control your leaf size by adjusting the amount of ammonia and phosphorus in your fertilizer mix. More will create a larger leaf, and less will create a smaller leaf. Ammonia is a type of nitrogen, but not all NPK mixes will have enough of the ammoniacal form of nitrogen. Ask your fertilizer sales rep for a detailed breakdown of your mix and consider choosing a mix where about 30% of the nitrogen is listed as “ammoniacal nitrogen” (see image of breakdown).
For phosphorus, 10% and above is considered a lot (so use less if you want smaller leaves), but you can go up to 20% if you are trying to significantly increase leaf size early in the crop. The flip side of using higher Phosphorus is that, besides larger leaves, your plants are also going to shoot up in size and risk becoming stretchy. It is imperative to increase your PGR applications accordingly when utilizing this strategy.
EC Monitoring
Monitoring your fertilizer levels in the pot is probably one of the most important things to do throughout the growing cycle. Meters for measuring EC in the media can be purchased fairly inexpensively and can be used for years.
Measuring the EC level in the growing media will help you make informed decisions on fertilizer applications, saving you headaches later on. It’s best to monitor weekly and take your measurements the day after fertigating, as these plants typically take the food they need within a day after application. If the plant is using the nutrients, your EC measurement will be low. If they are not, your measurement will be high.
For example, right after a pinch, you might notice that your EC readings in the pot will go up. This is because you’ve removed the growing tip, resulting in a temporarily inactive plant. If you observe an increased EC measurement in the pot, you may want to consider lowering or skipping a feed around this time to avoid burning the roots. Burned roots can cause a stressed plant, which makes your crop more susceptible to pests and diseases.
Track your EC readings with plant observations to create a playbook that can be used and built on year after year. Data is power in the greenhouse; the more you have, the more successful you will be.
Managing the Greenhouse Environment
Heat Stress
Managing heat stress in the greenhouse in July and August is a difficult task, especially when dealing with young plants. However, with new genetics and recommendations, it has become easier to manage over the years. The key is recognizing how heat stress presents itself in the crop and having a few key tools in your back pocket to manage it when it inevitably happens.
| What heat stress can look like: |
| – Distorted, leathery or curled foliage – Poor branching after pinching – Root loss – Flower abortion (in later stages of poinsettia production) |
| What you can do about it: |
| – Try to keep light levels low, especially after transplant. Use your blackout curtain if necessary. – Mist plants during the hottest periods of the day. – Never let the growing media completely dry out. – Consider irrigating plants in the afternoon when temperatures are extremely high for multiple days. CAUTION: Only do this on extreme heat days when you are sure that the foliage will dry before dusk. |
Use Temperature to Your Advantage
Remember that temperature differentials (DIF) can be very valuable for controlling plant growth. A negative DIF (cool day/warm night) can hold plants at a height. A positive DIF (warm day/cool night) can help to increase plant height. Stem growth is most active at dawn, so some growers choose to lower the temperature for only a few hours around dawn to reduce elongation, with good results.
Spacing
Pots that are too close together will have weak, elongated stems as the plant competes for light and resources with its neighbours.
Tight spacing can lead to uneven canopy expansion and contribute to disease and pest pressure in humid micro-climates (including Botrytis, especially in 4-inch pots where spacing is usually tighter!).
PGR Applications
This section was contributed to by Dr. Chevonne Dayboll
Most newer poinsettia varieties and hybrids have been bred to have a compact, upright shape so pinching and PGR application are perhaps not as critical as they were in the past (although every grower has their preference!). PGR mistakes can be costly, so the more information a grower can gather before deciding to spray, the better.
Graphical tracking of plant development against your sales specs (see Figure 1) for height and diameter can assist in making height management decisions, whether they are PGR applications or DIF adjustments.
To graphically track your crop over the season, measure and record the height of at least 10 plants of each variety that you grow weekly (different varieties may have different growth curves). Make sure to be consistent in measuring height from either the pot lip or the floor/benchtop. Indicate dates for any production changes or product applications and ensure the amounts and application methods of PGRs are noted as well.
Once you have a few seasons of this data, it’s easy to compare where you are to where you should be overall and make more informed management choices. Use the Ball Seed Poinsettia Growth Tracker Tool to manage your data or take a stab at making your own graphs in Excel.
Research out of MSU has shown that early low-dose drenches of Paclobutrazol (e.g. Bonzi) can effectively control height for poinsettia. However, the response by variety plays a big part in both the number of applications and the rate. In general, more vigorous varieties required more applications or a higher rate (details on what they found for specific cultivars in 2007 here). MSU has continued its work and has provided more information on ‘micro-drenches’ for poinsettias here.
In general, sprays of Daminozide (e.g. B-Nine) or Chlormequat Chloride products (e.g. Cycocel) will provide shorter-term inhibition of stem elongation which may be desirable for small height corrections or holding crops later in production.
Resources & New recommendations
Remember how much of a pain Points were to grow 10 years ago? 20 years ago? Too young to remember? Ask a seasoned Points grower for their battle stories. Here’s the good news – over time, it has become a (slightly) easier crop to grow as researchers, breeders and growers work together year after year to improve growing recommendations, genetics and pest control. Capitalize on the hard work of our community by always keeping up to date with the newest recommendations. Here are some for you to check out:
Production guides:
- Selecta 2025 production guide (skip to page 40 for the production guide)
- Syngeta 2021 production guide
Grower Talks: Tech on Demand shares great information on poinsettia production annually.
- Success with Poinsettias (Part 1) 2024 **great 1 hour podcast to throw in your earbuds while you do other tasks**
- Success with Poinsettias (Part 2) 2024
- Poinsettia Fertilization Tricks 2023
Poinsettia trial results:
- Ontario based 2023 trial results from Sawaya Gardens
- US based 2023 trial results from Plantpeddler and N.G. Heimos Greenhouses
E-Gro:
Pest resources: