Flowering Poinsettia Production

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Flowering Poinsettia Production

Although considered by some to be “hard to grow”, poinsettias are a relatively simple crop to produce. It is important that growers pay attention to the basics of production outlined in this technical sheet, use the resources available (web sites, extension assistance, etc.) and treat this crop much like other potted crops typically produced in greenhouses.

What you NEED to produce poinsettias:

Poinsettias require the controlled environment provided by greenhouses. The severity of the climate dictates how sophisticated systems for heating and cooling must be. Night temperatures must be maintained above 60°F/15°C but below 72°F/22°C to avoid delayed flowering. Day temperatures between 70 – 85°F/21 – 29°C allow for normal development, while temperatures above 90°F/32°C can cause excessive stress. An average temperature of 68°F/20°C is needed to assure proper flowering of poinsettias. Average temperatures cooler than this slow development while temperatures exceeding this increase the rate of development.

Reasonable water quality is important for use in irrigation and fertilization. Have the water tested to establish pH, soluble salts (E.C.), and the presence of any minerals or chemical factors that might influence plant development. Domestic water supplies are generally acceptable for poinsettia production, however the level of chlorine may become an issue at times. Waters that originate in ponds, wells, etc. are more variable in quality and require periodic testing to assure they are acceptable for plant production and not contaminated with pathogens such as Pythium. For more information on water quality and fertilization programs, contact the Scott’s Company and JR Peters testing laboratory (800) 743-4769.

Before starting a poinsettia crop, planning and research will help assure success. Growers need to have a sense of what they are trying to accomplish (finished size, desired forms, timing, etc.) before any cuttings are brought into the greenhouse. Many of the specifications needed to drive decisions about the crop come from understanding the target market for these plants. The characteristics required of this crop when sold through florists may vary from those sold through the chain store. Be sure the plant fits your market needs!

What you NEED TO KNOW about poinsettia flowering:

The true flower of the poinsettia is the small, yellowish structures that form in the growing tip known as cyathia. Bracts, the colored leaves for which the plant is known, are modified leaves surrounding flowers that develop pigmentation in response to flower initiation.

Poinsettias initiate flowers when days become shorter than nights. In the Northern Hemisphere, this day length condition naturally occurs during mid to late September and in the Southern Hemisphere, during March. Once short days begin, it is important that nights continue to get longer for bracts to form color. During this development stage of the poinsettia, if nights get shorter rather than longer the flowering will be disrupted and plants will fail to flower.

The phase of growth prior to flower initiation is referred to as vegetative growth, while the flowering stage is known as the reproductive phase. The flowering response time is the time, usually in weeks, required for the plant to develop to a mature, salable flowering plant from the date of flower initiation. This assumes all growing conditions are “normal” for the crop. Factors that might disrupt this development include temperatures, light intensities, nutritional disorders, and injury from insects, disease or chemical pesticides applied to the crop. Using the flowering response time, poinsettias can be scheduled for optimum development. This is accomplished by starting with the desired flower maturity date and working backwards using the flowering response time to determine when the crop needs to initiate flower in order to be ready for sale at the appropriate time. This factor will most likely influence which cultivars should be grown for best results.

Next, decide what size and height the finished plant should have to provide the correct vegetative growth time prior to initiation. Generally, the longer the amount of time allowed from time of pinch to time of flower initiation, the larger the size of finished plant. The climatic conditions typical of the region dictate how much growing time is appropriate. Growers in colder, Northern locations should start the crop early to assure adequate growth before days get too short and light levels get too low. Growers in warm, sunny Southern regions start the crop much later to be sure plants do not get too large in the warmer, more humid environment.

To produce good quality 6.5” pots (1 pinched plant per pot, 16-18” tall) an average of 3 weeks time from pinch to flower initiation is needed. For more vigorous cultivars slightly less time is acceptable. For slow growing cultivars, more time may be required. Plants in larger pots, usually with multiple cuttings per pot, should be started and pinched earlier to provide the amount of growth needed to achieve size. A good rule of thumb is to add 1 week of vegetative growth for every inch in pot diameter increased over the 6” pot.

For smaller forms (3”, 4”, etc.), less vegetative growth time is required to make it easier to maintain plants within the desired finish size without using excessive applications of growth regulators. Generally, 4” pots are provided 10 days of vegetative growth prior to flower initiation to achieve a finished height of 10”. More information specific to scheduling poinsettias is available on the Internet at www.ecke.com or in the Technical Information Bulletin on Crop Scheduling.

Most poinsettia forms require pinching which is the removal of the growing tip, or terminal to encourage development of lateral (side) shoots. Pinching can be done using a knife or by using fingers to “snap” the tip from the plants. A soft pinch will include removal of the tip and small, immature leaves only. If removal includes the first mature (fully expanded) leaf of the plant along with the smaller immature leaves and tip it is considered a hard pinch. Today’s poinsettias respond best to soft pinches that stimulate side shoot growth from young stem tissue.

The size of the finished poinsettia determines the amount of greenhouse space required by each plant. Large plants require more space, therefore become more valuable due to increased space and production costs (heat, cooling, etc.). Plants that are grown too tightly are prone to stretch and stem breakage. Plants that are grown with too much space do not take full advantage of the energy costs. A good balance needs to be found between good plant quality and profitability. For more information on suggested spacing by form, see The Poinsettia Manual 3rd edition, 1990.

What you NEED TO PROVIDE:

Containers: Most growing containers are acceptable for poinsettias. The container should have adequate drainage holes to assure proper drying/aeration of growing medium. Plants grown on the floor may benefit from drainage holes extending into the sides of pots, allowing water to drain when the pot is in full contact with the ground. Thin-walled containers that allow light to penetrate are less desirable than thicker walled pots, as light inhibits root growth. White pots are not desirable for this same reason.

Growing Medium: Poinsettias can be grown in most soil mixes, provided they are irrigated and fertilized properly. Mixes with adequate pore space for good aeration and good moisture retention work best. It is important that whatever medium is used, it is free of insects or diseases.

Fertilization: A fertilization program should be based on characteristics of water quality and growing media. No single commercial fertilizer is available to fill every poinsettia growth requirement. Most growers use a rotation of fertilizers to complement key growth stages. All essential elements must be supplied in appropriate rates and balances for optimum growth. The following suggests a “general” program to start with:

Establishing (transplant through pinch): Use a general-purpose fertilizer (20-10-20, etc.) alternated with calcium feeds (15.5-0-0, 15-5-15, etc.) at 200 to 250 ppm Nitrogen constant liquid feed (CLF).

Growing on (pinch through color development): Use the program outlined above with the addition of minor elements (STEM, or chelated elements) on a periodic basis to assure adequate supply of these critical minerals.

Finishing (color development through maturity/sale): Change the emphasis of the rotation to nitrate nitrogen programs (calcium or potassium fertilizers, etc.) and reduce rates of application to half of earlier levels. Approximately 2 weeks from sale drop all fertilizer and irrigate with clear water unless plants show symptoms of yellowing or other nutrient deficiencies.

Height Management: Height control may involve preventing internode stretch that causes plants to get too tall, or promoting stem elongation that allows plants to reach their desired height. The challenge is to understand when the appropriate action is required. Growers should measure and “track” the height of the crop to make good decisions about height control. There are computer programs available to assist with height tracking, or simple measuring sticks can be used. At the beginning of the crop, mark several plants in each product form and cultivar to use for height tracking. Once or twice weekly, measure and record the total height from the base of the pot (bench level) to the upper most growing point. By comparing this information from previous measurements it is possible to see how much, or how little, these plants grew. Although the weekly growth is not a linear equation (most cultivars plateau during the final 2-3 weeks of development), it gives the grower a reference to how much stretch is potentially left in the crop. Decisions regarding cultural manipulations such as DIF, additional spacing, growing temperatures, etc. or the use of chemical plant growth regulators (PGR’s) may be made based on understanding the actual plant growth and estimated growth potential for the crop. It’s important that PGR’s are mixed and applied at appropriate rates and dates to avoid distortion of bract size or color development.

Pest Management: Poinsettias may be attacked at any point by various insects or diseases. Monitor plants and their root systems through plant inspection and yellow sticky cards throughout the crop. It is possible to maintain a clean and healthy crop to market. Throughout production, look for the following:

Fungus gnats, specifically the larval (immature) stages damage poinsettias by feeding on roots or stems. This pest is readily found in decaying organic matter in greenhouses and moist growing media.

Whiteflies cause damage to the crop by feeding on plant tissues. An additional problem, known as “sooty mold” results from whiteflies feeding on the undersides of the leaves. A sugar-rich liquid, known as honeydew, is produced by whiteflies and cover leaves directly below the feeding insect. This honeydew is an ideal food source for the dark, sooty mold. Although the fungus itself is not pathogenic, it does cover leaves, blocks light and limits photosynthesis.

Thrips, although not a major pest of poinsettias, have been known to cause damage to the leaves and bracts. Generally these pests are the most abundant during late summer and early fall as alternate host plants are removed from the greenhouse or surrounding area.

Mites have also caused damage to poinsettias when the pest is present in adjacent greenhouse crops.

Stem and root rots can attack poinsettias at any time in the crop development. Good sanitation practices and proper soil moisture management can minimize the risk of either of these rots getting established. It is not unusual for growers to use a broad-spectrum fungicide or mixture at the time of transplanting to prevent these diseases from getting established. This is the time of greatest risk for contamination and introduction of diseases. After this initial application, follow up treatments can be used on a periodic, or as-need basis.

Foliar diseases like Botrytis or powdery mildew can also attack poinsettias. As these pathogens are more likely to develop in the later stages of development, a preventative program is suggested to minimize the risk of these diseases.

Shipping and Handling: Once finished, poinsettias should be maintained in the greenhouse at cooler temperatures than used for growth and development. When bracts are fully colored and expanded, reduce day and night temperatures to about 60°F/15°C to intensify color, reduce speed of cyathia drop and “tone” plants prior to market. The final process is transporting plants to the customers. For some, this may involve nothing more than customers coming to the retail to select and pay for their plant before taking it home. For others, this process may involve extensive packaging and transportation to warehouses for redistribution. The extent of handling dictates what level of packaging will be required. The goal through shipping is to prevent damage to bracts and leaves while minimizing the breakage of stems. Poinsettias are usually sleeved using any of the commercially available sleeves (paper, plastic, fiber, or combinations of these materials). These sleeves need to have sufficient outward flare to prevent damage from stems and bracts being held too closely. Likewise, they should not be too loose causing damage when plants move and “rub” during transportation. Boxes offer a means to transport multiple plants in one container, facilitate protection from cold as well as allow for stacking in a truck and increase the number of plants that can be transported at a time. Like the sleeves, boxes should hold plants tight enough to prevent excess movement without damaging plants from being too tightly packaged. Boxes can be purchased in a variety of sizes. Check with local manufacturers to find containers that fit your specific needs.

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