This post was contributed to by Abigail Wiesner, Drs. Sarah Jandricic, and Chevonne Dayboll.
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, PGR mistakes and early diseases can all be costly in this high-value crop. Read on for common pitfalls and how to avoid them, as well as links to pest management information in early production.
Probably the biggest threat to your poinsettia crop is starting to get lax with your growing. But it can be hard to keep up with the latest production tips and tricks for all the different ornamental crops we grow. I’ve included a few relevant articles pertaining to poinsettia production below that provide additional info and some different opinions to consider!
Grower Talks: Tech on Demand shares great information on poinsettia production annually.
Poinsettia trial results:
E-Gro:
Beyond knowing the latest pointers, the best thing you can do for your crop is to MONITOR, MONITOR, MONTOR! Keeping plants as “stress-free” as possible will ensure the highest rate of plant success.
Typically, water soluble feeds are used in poinsettia, but a few growers have been trialing controlled release fertilizers (CRFs) for poinsettia production with good results. The CRF evens out nutrient availability between liquid feeds and can allow you to fine tune your fertilizer program throughout production by adding in liquid feed where and when necessary. Talk to you supplier about your options and ask them for recommendations and trial results if you are considering trying a CRF/liquid feed nutrition program.
“Christmas Day” poinsettias showed little to no difference in height & plant mass after finishing with 0, 25, 50 and 100% of the recommended levels of Mo. (Credit: Study by J. West, FCO & W. Brown; 2015)
Molybdenum (Mo) has always been considered a limiting nutrient for poinsettias, but research done by OMAFA and Flowers Canada has shown that it may not be as critical in the final stages of production. In their study, they looked at reducing the rates of molybdenum once rooted liners of the variety “Christmas Day” were spaced, and there were no significant differences in height or weight of the plants finished at 100%, 50%, 25% or 0% of the recommended Mo level. The lower levels (0 and 25%) showed a decrease in Mo levels in plant tissues, but no visible deficiencies were seen at the shipping date. Its important to note that this study didn’t look at propagation or young plant development, where fertilizer recommendations for all nutrients, including Mo are still suggested.
Misting cuttings
Temperature control
An example of properly spaced poinsettias as bracts begin to colour.
Spacing
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 making a decision to apply is better.
Graphical tracking of plant development against your sales specs for height and diameter can assist in making height management decisions, weather they are PGR applications or DIF adjustments.
Example growth curve for a greenhouse crop such as Poinsettia.
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.
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.
There are several diseases you should start scouting for NOW, under the misting bench:
Other root rot diseases in plug trays (including Pythium, Phytopthora, Rhizoctonia and even Fusarium) proceed slowly, and won’t kill the rooted cutting outright. Make sure you’re regularly inspecting your cuttings to get the jump on these diseases.
Evidence of root rot including poor rooting, stunted growth, discoloured (black or brow) roots, loss of lower leaves, or cankers on stems. If you see these, then you’ll seriously want to consider getting the disease identified by the Guelph Lab Services so you can make a plan of attack.
Phytophthora crown rot. The pathogen is Phytophthora drechsleri, which causes a root rot that may extend upwards into the lower stem. It is not possible to distinguish this injury from that caused by Pythium aphanidermatum, which is also commonly found on poinsettias. Photo courtesy of Cornell Cooperative Extension
Generally, with any root rot, here’s how to get on top of it:
If these steps are followed, there’s a good chance you won’t start losing plants in September and need to follow up with even more applications of chemical fungicides.
Concerned about pests like whitefly, mealybug and Lewis mite in early production? Then check out this pest management blog post from 2023:
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, PGR mistakes and early diseases can all be costly in this high-value crop. Read on for common pitfalls and how to avoid them, as well as links to pest management information in early production.
Staying On Top of New Recommendations
Probably the biggest threat to your poinsettia crop is starting to get lax with your growing. But it can be hard to keep up with the latest production tips and tricks for all the different ornamental crops we grow. I’ve included a few relevant articles pertaining to poinsettia production below that provide additional info and some different opinions to consider!
Grower Talks: Tech on Demand shares great information on poinsettia production annually.
- Success with Poinsettias (Part 1) 2024
- Success with Poinsettias (Part 2) 2024
- Handling Hot Poinsettia Cuttings 2020
- 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:
Beyond knowing the latest pointers, the best thing you can do for your crop is to MONITOR, MONITOR, MONTOR! Keeping plants as “stress-free” as possible will ensure the highest rate of plant success.
Proper Nutrition
Typically, water soluble feeds are used in poinsettia, but a few growers have been trialing controlled release fertilizers (CRFs) for poinsettia production with good results. The CRF evens out nutrient availability between liquid feeds and can allow you to fine tune your fertilizer program throughout production by adding in liquid feed where and when necessary. Talk to you supplier about your options and ask them for recommendations and trial results if you are considering trying a CRF/liquid feed nutrition program.
“Christmas Day” poinsettias showed little to no difference in height & plant mass after finishing with 0, 25, 50 and 100% of the recommended levels of Mo. (Credit: Study by J. West, FCO & W. Brown; 2015)
Molybdenum (Mo) has always been considered a limiting nutrient for poinsettias, but research done by OMAFA and Flowers Canada has shown that it may not be as critical in the final stages of production. In their study, they looked at reducing the rates of molybdenum once rooted liners of the variety “Christmas Day” were spaced, and there were no significant differences in height or weight of the plants finished at 100%, 50%, 25% or 0% of the recommended Mo level. The lower levels (0 and 25%) showed a decrease in Mo levels in plant tissues, but no visible deficiencies were seen at the shipping date. Its important to note that this study didn’t look at propagation or young plant development, where fertilizer recommendations for all nutrients, including Mo are still suggested.
Environment – Temperature and Humidity control
Misting cuttings
- Misting is important for keeping cuttings turgid (they don’t have roots!)
- Mist so the leaf surface is constantly moist without over wetting the media. Over wetting the media can promote soft rot by Pectobacterium (Erwinia)
- Maintain relative humidity in the prop environment at near 100%.
- Mist based on the cuttings, not what has “always worked”.
Temperature control
- Establishing cuttings during a nightly heat wave? If possible, reduce night temperatures to 18˚C during the first few nights after sticking. Lower night temperatures help cuttings get established faster.
- Leaves rolling inward are a sign of dry cuttings in a HOT environment. Use shade curtains and propagation tents 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.
An example of properly spaced poinsettias as bracts begin to colour.
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!).
Proper Application of PGRs
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 making a decision to apply is better.
Graphical tracking of plant development against your sales specs for height and diameter can assist in making height management decisions, weather they are PGR applications or DIF adjustments.
Example growth curve for a greenhouse crop such as Poinsettia.
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.
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.
Diseases in Propagation That Can Sideline You in September
There are several diseases you should start scouting for NOW, under the misting bench:
- The bacterial rot Erwinia (now called Pectobacterium) is the one of the first diseases to appear in poinsettia. Check for soft, mushy, smelly cuttings, starting at the base of the stem and moving upwards.
- Rhizoctonia can also cause problems early in the crop and exhibit similar symptoms as Pectobacterium (without the funky smell). You may also see white fungal strands near the crown.
Other root rot diseases in plug trays (including Pythium, Phytopthora, Rhizoctonia and even Fusarium) proceed slowly, and won’t kill the rooted cutting outright. Make sure you’re regularly inspecting your cuttings to get the jump on these diseases.
Evidence of root rot including poor rooting, stunted growth, discoloured (black or brow) roots, loss of lower leaves, or cankers on stems. If you see these, then you’ll seriously want to consider getting the disease identified by the Guelph Lab Services so you can make a plan of attack.
Phytophthora crown rot. The pathogen is Phytophthora drechsleri, which causes a root rot that may extend upwards into the lower stem. It is not possible to distinguish this injury from that caused by Pythium aphanidermatum, which is also commonly found on poinsettias. Photo courtesy of Cornell Cooperative Extension
Generally, with any root rot, here’s how to get on top of it:
- Rogue out any infected plants immediately to make sure the inoculum doesn’t spread. This only works along side good sanitation.
- Once you’ve had your disease identified, apply an appropriate preventative chemical fungicide in propagation to help knock it back.
- Follow this with an application of a broad-spectrum microbial fungicide like Actinovate SP, PreStop, Rootshield, Taegro or Trianum on rooted cuttings that will boost root growth and help fight off disease. You may even be able to drench these directly with the chemical fungicide you’re applying, depending on the chemical. Check out the new Crop Protection Hub website to learn about products, help select the most appropriate one and check the label to see if tank-mixes are allowed!
- Don’t over-fertilize or over-water plants, as this can promote disease.
- Keep your greenhouse sanitary: these means no hoses on the ground, no pools of algae or potting mix on the floor that can promote pests like fungus gnats, which can spread plant disease.
- If necessary, control fungus gnats with applications of nematodes or insect growth regulators like Citation or Dimilin as soil drenches.
- Repeat up your microbial fungicide applications RIGHT at potting. This step is key in continuing the fight disease as they get placed in a bigger container.
If these steps are followed, there’s a good chance you won’t start losing plants in September and need to follow up with even more applications of chemical fungicides.
Insect Pest Management:
Concerned about pests like whitefly, mealybug and Lewis mite in early production? Then check out this pest management blog post from 2023: