Growing in the Green: Assessing the season

February 07, 2012
Written by Melhem Sawaya

 Green1  
Arie Koole (Creekside Greenhouses) likes the habit and look of ‘Novia.’
 
Here are some of the challenges that every grower has to deal with every poinsettia season:
  • An ever-increasing number of new varieties.
  • Lack of practical culture information on how to grow the new cultivars.
  • If such information is available, it usually pertains only to certain geographic areas and not to all regions – which makes it even more confusing.
  • The weather is never the same from one year to the next, so trying to follow exactly the same environmental parameters could be a disaster.
  • Introduction of a new soil mix without proper testing.
  • Introduction of a new chemical (pesticide, fertilizer, wetting agent or any other new product) without much – or any – testing, which results in thousands of dollars in shrinkage. This is an important point: the number one shrinkage factor in the horticulture industry is the introduction of new products without proper testing.
  • Introducing a new cultivar to the buyer, and then having it forced on the grower, leads to a crop with lots of advertising money spent on it, and yet it’s a product that cannot be delivered by the grower because:
  1. Its newness creates growing challenges.
  2. We do not know the consumer appeal for that cultivar.
  3. The breeder or variety broker is not ready to ship quality cuttings to the grower and they, themselves, don’t know exactly how to grow that specific crop because it is also new to them.  So, before trying a new cultivar on a large scale, test it for:
  4. Production know-how.
  5. Customer appeal – which is more important.
  6. Shipping and shelf life at the consumer level.

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Jessica Rooker and Aaron Dunlop (Terra Greenhouses and Garden Centre) show how ‘Winter Sun’ can be grown in large or small pots.

SALES AND PRODUCTION
The past season was a different year for Ontario poinsettia sales and production, largely due to the weather. Sales started very slow but, in the end, the entire crop was sold. This is the third year in which production met market demand.

However, I hasten to add that the few growers who increased production by five per cent still had that five per cent in their greenhouses at the end of the season.


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Pete van Beurden (Westland Greenhouses in Jordan Station) says ‘Prestige’ performed very well for them last season.
And while most of the greenhouses were empty, I still have to wonder about sell-through in the stores. This is a major concern, because if stores don’t make a profit on an item, it means they will buy much less or eliminate it completely the next year.

There are a few growers who still grew on speculation, hoping that some grower/broker would take it off their hands. This didn’t pan out either and for the following reasons:
  • The season started late and every grower/broker naturally wants to ship their own crop; if they need more product, they will then try to find it.
  • The weather was perfect for bud-set because the temperature in late September (when bud-set is supposed to take place) was perfect.
  • We had the highest October and November light levels that I can remember for the last 30 years.
The combination of both weather conditions led to having many poinsettia varieties ready to ship Nov. 5-7. With normal natural light levels, they would not have been ready until Nov. 25.

The other factor was that with such nice weather, and with outdoor temperatures in the teens, people were not thinking of indoor decorations. On the other hand, sales of greens increased by 10-20 per cent again this year.

The early bud-setting and large bract development did not lead to cultural problems at the end of the shipping dates, even on overly mature bracts.
Many of the new varieties branch freely under normal conditions. The reality is that we’re rarely growing plants under normal conditions, although we always strive for them or try to avoid conditions that negatively impact branching.
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Green5
Steve Valstar (Scott Street Greenhouses) likes his ‘Premium’ in 12” pots. Dan Newhouse (Waldan Gardens) always looks forward to the poinsettia season.


OBSERVATIONS ON BRANCHING

  • This past season, few growers had less-than-optimum poinsettia branching.
  • The symptoms are on respectively older varieties.
  • The symptoms varied from one pot size to another of the same variety.
  • By far the best branching was on 4” direct stick plants.
  • Branching varied with the calibre of the cuttings.
  • Older cuttings (over 21 days) can lead to uneven branching or minimal branching.
  • Crowded plants have more advanced top branching.
  • Plants that were under stress from extreme heat showed no breaks.
Here is a summary of the factors that will result in poor branching.
  1. Excessively hardened cuttings.
  2. Excessive low or high light, high temperatures and too-low humidity. This does not mean saturated media, which will slow rooting drastically. It means high humidity with media “just moist.”
  3. No spacing.
  4. No low rates of growth regulators. Low, frequent applications of 1,000 ppm Cycocel will allow the lower breaks to catch up with the higher ones.
  5. Tall cuttings.
  6. Hard pinch on old, stretched cuttings.
  7. Large bracts due to finishing the crop at warm day temperatures (above 20 degrees).
  8. Loss of phytoplasma that exist in the phloem of the poinsettia plant. Phytoplasma reacts with a poinsettia genome (genetic material) and this reaction initiates a hormone responsible for free branching. Phytoplasma may also change the appearance of a poinsettia, and the response varies by variety. Heat stress conditions (high light, high heat, low moisture) during propagation and the establishing phase can actually eliminate phytoplasma, resulting in:
  • Poor branching.
  • Uneven branching development.
  • Physical appearance not characteristic of a particular variety.
Here is more information about phytoplasmas, since it could be information you’re reading for the first time.

Phytoplasmas are prokaryotes lacking cell walls that are currently classified in the class Mollicutes (Agrios, 1997). Phytoplasmas are associated with plant diseases, and are known to cause more than 600 diseases in several hundred plant species (Kirkpatrick, 1992; McCoy et al., 1989).

The symptoms shown by infected plants include:
  • Yellowing or reddening of the leaves.
  • Shortening of the internodes, with stunted growth.
  • Smaller leaves.
  • Excessive proliferation of shoots, resulting in a “witch’s broom.”
  • Virescence (the state of being green or the process of becoming green, especially the abnormal development of green coloration in plant parts that are not normally green, as a result of disease).
  • Sterile flowers.
  • Necrosis.
  • General decline and death of the plant (Kirkpatrick, 1992; McCoy et al., 1989).
Phytoplasmas are transmitted from plant to plant by insect vectors, mainly leafhoppers and psyllids (Ploaie, 1981). They traverse the wall of the intestinal tract, multiply in the hemolymph, and pass through the salivary glands, in which they multiply further. Then, the insect vectors introduce phytoplasmas along with salivary fluids into the phloem of a new host plant (Agrios, 1997).

Usually these insect vectors do not transmit phytoplasmas transovarially, although two exceptions have been reported: aster yellows and mulberry dwarf phytoplasmas (Alma et al., 1997; Kawakita et al.; 2000).

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Ed Jr. and Ed Sr. (Ed Sobkowich Greenhouses) rush this variety to shipping.

BRACT EDGE BURN (BRACT DISORDER)
Bract disorders have many causes, not just calcium deficiency. The highlight connection between calcium deficiency and bract disorders overshadows other causes because some tests show that sprays of calcium can minimize the symptoms. As growers, we mainly concentrate on how to correct the problem rather than how to prevent it – just as we take Aspirin, Tylenol or some other medicine to get rid of a headache instead of finding the cause of it.
I used to get severe headaches but only on the weekends and, yes, I took the pain pills and felt drowsy, but without pain. Then, for some reason, I decided to switch from caffeinated to decaf coffee and, after three weeks, the weekend headaches disappeared. I realized the cause of my headaches was the sudden withdrawal – every weekend – from the normal six to eight cups of caffeinated coffee I drank each weekday, to the weekend where I drank no coffee at all!

Getting back to plants, another example of correcting the symptoms rather than preventing the cause is applying iron chelate to counter yellow tips on calibrachoa or petunias. While there are many ways to prevent yellowing on calibrachoa, there are also many ways to prevent Bract Edge Disorder on poinsettia. Here are some of them:

Reduce humidity in the greenhouse: If humidity is too high, the plants are getting most of the moisture in the air on their leaves. This means the roots don’t have to work as much, or hardly at all, and any nutrients that we provide are not getting to where they belong.

The worst scenario is when we use flood-floor irrigation, or some other kind of sub-irrigation, where the heat is delivered primarily from the bottom, which evaporates much of the water from the pot and builds up humidity. This humidity damages the root tips, which then prevents the nutrient uptake, leading to some nutrient deficiencies.

That is why many greenhouses – mainly vegetable greenhouses – have suspended heat pipes installed with adjustable cables to enable them to position the heat just above the leaf canopy so the plant will work on absorbing all nutrients provided to them.

Use a media that drains well: Well-draining media is used to avoid root growth without the hairs that are the implement of nutrient transportation. It is what I call “avoiding swamp roots.”

Maintain good root growth: Establish a healthy root system early on in the crop. A strong, well-rooted plant will more easily withstand minor, unfavourable plant growth conditions.

Reduce fertilizer EC: High salts at the finishing stages of the crop could lead to bract disorders if the crop dries up too much. This by no means suggests stopping fertilizing completely.

Avoid pesticides on bracts: Some pesticides, if applied at bract colouring or even earlier, could and will cause bract edge disorder. Thiodan is one example.

Balance fertility: Maintain proper ratios of potassium, calcium and magnesium. The proper ratio is: potassium = 3, calcium = 2, and magnesium = 1; but the total EC for the last three weeks should be 0.5-0.6.

Provide a calcium uptake environment: Make every effort to ensure nutrients are being taken up by the roots. For example, horizontal airflow fans are important for two main reasons:
  1. They provide a gentle air movement that will encourage evaporation, which will then encourage nutrient uptake.
  2. They will even out the temperature throughout the various locations in the greenhouse.
Also, make sure the pH is between 6.0 and 6.5, because calcium is not available at low pH levels.

Select the correct cultivars: Select cultivars that are resistant to Bract Edge Burn.

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A sold-out greenhouse … the only time poinsettia is especially profitable.

If all this fails, some experiments showed that spray applications of calcium could be helpful. A spray of 300-400 ppm of calcium will supplement calcium buildup in the bracts. Spraying the bracts has to happen when leaf temperatures are not very high and it is better to spray early in the morning to allow the bracts to dry before sunset.

Use only a high-grade purity of calcium if you decide to spray calcium.

To take full advantage of the calcium sprays you must start spraying as soon as the bract colour shows and continue spraying every six or seven days until pollen shed.

Bract Edge Burn was minimal or negligible this past season, regardless of whether calcium sprays were applied or not. The main reason was the high solar energy that prevailed through the months of October and November. Growers are also more proactive in working to avoid it.

Another factor is that considerably fewer chemicals are being used. Historically, we know that some chemicals can cause Bract Edge Burn or symptoms similar to it.

If we learned anything from this season’s poinsettia crop, it was that about 10 per cent of sales occurred between Nov. 10 and 24, some 70 per cent between Nov. 25 and Dec. 10, and the remaining 20 per cent from Dec. 11 to 20.

The key take-home lesson is that old, ripe bracts are a cause for problems and timing the crop according to these projections is a very important aspect of a successful season.

And last, but not least, poinsettias can be profitable if no shortcuts are taken, and if you grow only what is sold and give the plants enough space and all the natural light possible.

Melhem Sawaya of Focus Greenhouse Management is a consultant and research coordinator to the horticultural industry. Comments on this or any other article are always welcome via
This e-mail address is being protected from spambots. You need JavaScript enabled to view it , or visit www.focusgreenhousemanagement.com or www.sawayagardentrials.ca.

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