POINSETTIA

Commercial Greenhouse Production



Scientific Name: Euphorbia pulcherrima

Family: Euphorbiaceae



Dr. J. Raymond Kessler, Jr.

Auburn University



Introduction

The poinsettia is native to southern Mexico and northern Guatemala around the area of Taxco Mexico (25 miles south of Mexico City). It was cultivated by the Aztecs in Mexico and the flowers was considered by them a symbol of purity. It is unknown how the flower became associated with the Christian holiday of Christmas. But in the 17th century, Franciscan priests settled near Texco Mexico and began using the flower in holiday celebrations because it was one of the few plants in bloom around Christmas. Poinsettias were first introduced to the United States in 1825 by Joel Robert Poinsett who was the first U.S. ambassador to Mexico. In 1902, Albert Ecke arrived in the U.S. from Germany and began growing poinsettias as field-grow cut flowers in California. In the 1920s and 1930s, poinsettias become the sole enterprise of the Ecke family and the family name to this day is synonymous with the poinsettia in the U.S.

Cultivars

The 50 or so commercial cultivars that were grown before 1960 were sports selected from large numbers of seedlings. Today, breeding is targeted for a wide range of specific characteristics only one of which is flower color. The top 10 cultivars grown in 1993 were:

The main cultivars used in the southeast are Gutbier V-14 Glory, Eckespoint Freedom, and Gross Supjibi. By far the most widely grown flower color is red followed by pink, white, and various bicolor combinations of red and white or pink and white. One yellow-flowered cultivar ("Lemon Drop") is available.



Eckespoint Freedom Red 18% Eckespoint Red Sails 5%
Gross Supjibi Red 12% Annette Hegg Top White 3%
Gutbier V-14 Glory 11% Gutbier V-17 Angelika White 3%
Annette Hegg Dark Red 11% Eckespoint Jingle Bells 3 3%
Eckespoint Lilo Red 11% Eckespoint Pink Peppermint 3%
Eckespoint Celebrate 2 Red 5% Annette Hegg Hot Pink 2%


The Flower

Actually, the conspicuous part of the flower is not the flower, but modified leaves called bracts. The actual flowers are located in the center at the base of the bracts. The flower forms are known as cyathia and occur in separate male and female forms. One standard way to tell when poinsettias are ready to ship is when the cyathias open and the stamens or styles protrude from the flower.

Propagation Alternatives

Growers may start a poinsettia crop in three ways: 1) Order cutting to grow stock plants from which cutting are taken for production, 3) Order unrooted cuttings to root in-house for production, or 3) Order rooted cuttings which are transplanted to the finishing container. It is essential to order the highest quality propagation material that is certified free of disease.

Stock Plant Production

Stock plant culture must be carried out with care to produce a sufficient quantity of quality cuttings for the Christmas crop. Only well-grown vigorous stock plants can produce the number of cuttings needed with the reserves required to perform well in propagation.

The stock plant growing facility should have the equipment needed to control light intensity, photoperiod and temperature. For maximum growth, stock plants need a minimum 65F nights and 70-80F days. Light levels for stock can be between 3500 and 6000 ft.ca. depending on ambient air temperature. Temperatures during the day should not exceed 85F which, during the summer, requires cooling pads. If cooling pads are not available, shading may be necessary to sacrifice light and control day-time temperature.

Lilo, Freedom, Red Sails, and Supjibi stock are sensitive to daytime temperature 85F or greater resulting in poor breaking after the pinch. During stock plant spacing, these plants should be placed in the coolest areas of the greenhouse. In addition, Freedom should be placed in areas of the greenhouse with lower light and lower temperature. Cultivars such as 'V-14' and 'Heggs' can tolerate a little more warmth.

The stock plant facility should have an automatic irrigation system with fertilizer injection. Since stock plants grow relatively large and are produced during the summer, the medium must be irrigated frequently, sometimes 2-3 times a day. A complete fertility program should begin at the time of potting. Cuttings deficient in any nutrient will not perform well in propagation. It is important to monitor fertility carefully. If only part of the stock crop can be put on automatic irrigation, hand water the most vigorous cultivars, ie. Heggs, and automatic water the least vigorous, ie. J. Bells, Freedom, Supjibi, whites, and some pinks.

Plantings before about mid-May should receive artificial long days using 10 ft.ca. incandescent light form 10:00 PM to 2:00 AM. Supplemental carbon dioxide has very positive effects on poinsettia stock plants and can be used where practical at 800-1000 ppm.

Stock Source

Rooted cuttings are purchase from a specialist propagator each year to ensure disease and insect-free stock. Cuttings are received from April to June for cutting production in July through September. The cuttings should be potted and watered in upon arrival. Inspect cuttings carefully for damage in shipping and the presence of insects or disease.

Containers

Container size depends on the planting date. Earlier planting dates require larger containers and later dates, smaller containers. Plant rooted cuttings directly in the final container. Potted cutting should be water in well (by hand the first time) and drenched with a broad-spectrum fungicide. Early stock are often maintained pot-to-pot until space becomes available after bedding plants before being placed at final spacing on automatic fertigation. Adequate spacing between stock plants not only encourages strong, healthy cuttings but makes it easier to pinch, harvest, and generally work with the plants.



Stock Plant Potting Options
Month Planted Container Size Spacing Cuttings/Plant
March 1 12" 1818" 35-40
April 1 10" 1515" 25-30
May 1 8" 1212" 18-22
June 1 6" 88" 7-10


Media

The primary focus in choosing media components for stock plant production should be the ability to sustain a healthy root system and provide nutrient and moisture holding capacity over a long cutting production period (as long as 6 months). Media components chosen should be stable enough to maintain aeration and drainage over the life of the stock plants. Some media components might include peat moss, barks (small percentage), perlite, rockwool, gravel or sand, and calcite clays. Generally, media for poinsettia stock production should be more course and well-drained than for many other greenhouse crops.

Pinching

Pinching is used to develop a strong stock plant structure and control the number and quality of cuttings produced. A pinch should include one unfolded leaf and the shoot apex, approximately -1". To insure lateral breaks develop uniformly, remove the upper 1-2 maturing leaves. Pinching schedule:

First pinch 2-3 weeks after potting. Pinch to leave 8-9 nodes, expecting 6-8 shoots to develop.

Second pinch 4-5 weeks after the first leaving 4-6 nodes, expecting 2-3 shoots to develop.

Third pinch 4 weeks after the second leaving 3-4 nodes, expecting 2-3 shoots to develop.

The first harvest can begin 4-7 weeks after the last pinch (often called the "critical pinch").

The timing of the first pinch should be when the roots have reached the bottom of the pot. After the first pinch, spread the second and third pinch pinches over a 3 week period depending on cultivar vigor and rate of lateral shoot development. This will spread out the harvest peak. Pinches from early stock can be rooted for additional stock.



Stock Schedule: Harvest Jun 24 - Aug 1
Plant Mar 1 Wk 10
1st Pinch Mar 18 Wk 12
2nd Pinch Apr 15 Wk 16
3rd Pinch May 20 Wk 21
1st Harvest Jun 24 Wk 26
Plant Apr 1 Wk 14
1st Pinch Apr 21 Wk 17
2nd Pinch May 13 Wk 20
1st Harvest Jun 24 Wk 26
Plant May 1 Wk 18
1st Pinch May 13 Wk 20
2nd Pinch Jun 3 Wk 23
1st Harvest Jul 1 Wk 27
Plant May 27 Wk 22
1st Pinch Jun 17 Wk 25
1st Harvest Jul 22 Wk 30


Fertilization

1) Begin at the time of planting with 250-300 ppm N if the medium does not already have nutrients.

2) Reduce to 200-250 ppm N once roots reach the bottom of the pot.

3) Maintain medium pH 5.8-6.3 and EC 1.5 mmhos/cm (2:1) or 3.0 mmhos/cm (saturated paste).

4) Chart pH and EC, at least monthly soil analysis, and records of fertilizer/water applications.

5) High ammonium fertilizers (20-10-20, 40% NH4) can be used early to promote rapid growth. This should be reduced to a lower ammonium fertilizer (<20%) several weeks before cutting harvesting to harden cutting growth.

Scheduling

Stock plant scheduling is important to quality control in obtaining vigorous uniform cuttings when they are needed. The following information should be kept to plan future stock plant needs:

Last year's shipments by week and cultivar.

Last year's cutting yields by week and cultivar.

Expected marketing trends by color and/or cultivar.

Last year's production records.

Generally, earlier stock crops will produce more cutting per plant and require fewer stock-plants (initial cuttings). However, more skill and labor is needed in training and cultural practices. Later stock crops will produce fewer cuttings per plant and require more stock-plants. More growers are choosing the later stock crop option (Late April to May) to have that greenhouse space available for bedding plants.

The number of nodes left on the plant after pinching/cutting determines how many new cutting will be produced. Manage the number of nodes left on the plant (generally 3-5) according the future production required. Scheduling the time of pinching stock plants is probably the most important factor to providing the desired number of cutting for a particular propagation date. Under good growing conditions, pinching or cutting harvesting may be done as soon as every four weeks. However, plants should not go longer than 5 to 7 weeks between pinching/cutting to prevent overgrowing and hardening off. If cuttings are not needed for production, discard them.

Propagation

Sanitation is probably one of the most important aspects of poinsettia propagation. All surfaces should be disinfected before cutting are stuck. All weeds should be removed from the propagation area because they may be hosts to many insects including whitefly and spider mites.

Cuttings

Cuttings are usually taken from mid-July to September, a time of year when care must be taken to control moisture stress. Many growers harvest cuttings very early in the morning (4:00-8:00 AM). Terminal cuttings are taken 2 to 3" long by snapping the stem or with sharp knives. The cutting should have at least 2 mature leaves. If knives are used, dip them is disinfectant between each stock plant (1 household bleach : 10 water). All employees handling cuttings should wash their hands with soap and water then rinse with disinfectant. Place the cutting in disinfected plastic bags or other container out of sunlight to retain moisture until stuck in the propagation area. Cuttings should never wilt! Some growers use a rooting hormone while others do not. If used, apply 1500-2000 ppm IBA or NAA either as a talc formulation (Hormodin #1) or in an aqueous solution. Apply only to the basal 1" of stem. Cuttings should be stuck in the rooting medium so that leaves do not cover the shoot tip of adjacent cuttings. Stick the cutting no deeper than -1" deep.

Media used for rooting poinsettia cutting may be trays filled with peat-lite media, Jiffy 7's, Jiffy 9's, peat blocks, Oasis, Root-Cubes or directly in the final container. The propagation temperature should be 70F night / 70-80F day and light 2500-3000 ft.ca. Shading of the propagation area may be needed.

The mist frequency is dictated by environmental conditions, however the cuttings should stay turgid without so much mist to leach nutrients form the leaves and media. A suggested frequency is 12 seconds on every 4 to 6 minutes for the first 3 to 4 days. After about 8 days, callus will form at the based of the cuttings and mist frequency can be reduced to every 8 to 10 minutes. By 14 to 18 days, roots should be present and the mist can reduced to every 30 minutes. Fertilization of the cuttings can begin at the time of callus at 100 ppm N using a balanced fertilizer. This is applied once a day at the end of the day after the mist is turned off. Cuttings are usually ready to transplant in 4 weeks.

Transplanting

To a large extent, the choice of container sizes for poinsettias is determined by the market. By far the most popular container size is the 6" pot, though poinsettias are commonly grown in pot sizes ranging from 4" to 8". Four and six inch pots are usually planted with one rooted cutting per pot, pinched. However, there is a market for 6" pots with 3 cuttings, unpinched. Larger pots may also be planted with more than one cutting per pot. Special hanging baskets are also used for poinsettias and stock plants may be forced for large plants. Special schedules and techniques are also used to grow poinsettia trees.

Media

Media for growing poinsettias should be on the course side and exceptionally well-drained. The pH should be 5.8-6.4. Poinsettias are more susceptible to calcium and magnesium deficiencies than many plants, therefore, 8-10 lbs/cu.yd. dolomitic limestone is added at mixing with at least 10% magnesium. Superphosphate is usually added at a rate of 4.5 lbs/cu.yd. and micronutrients at the rate recommended by the manufacturer. A starter supply of nitrogen and potassium is also added as calcium nitrate and potassium nitrate each at 0.5-1.0 lbs/cu.yd.

When transplanting rooted poinsettia cuttings to final containers, always plant shallow, no more than " deeper than in propagation. Deep planting can cause poor root development and increased potential for disease. When the cuttings were rooted in artificial cubes or blocks, do not plant to high or the propagation material will act as a wick and dry the roots.

Newly potted cuttings should be watered in immediately, preferably with a broad-spectrum fungicide. If just out of propagation, the cutting should be misted by hand several times a day under warm, bright conditions until root growth begins.

Water

A dependable source of high quality water is an important consideration in growing poinsettias. The alkalinity of the water should not be so high as to drive the pH of the medium above 6.5 or micronutrient deficiencies can occur. The total soluble salts and presents of nutrients or toxins should also be known.

Poinsettias can be watered overhead during early stages of production but moisture on the bracts is highly undesirable. Therefore, crops should be placed on an automatic watering system at or soon after spacing. Subirrigation is effective for poinsettias.

Fertilization

Poinsettias are generally heavy feeders, especially during early production. Fertilization should begin as soon after potting as possible depending on how much starter nutrition has been added to the medium. Fertility programs vary widely and may include liquid fertilization or liquid in combination with slow release fertilizers. However, success depends on raising the initial fertility quickly, then tapering-off toward the finish of the crop. Liquid fertilization at 300 to 400 ppm nitrogen (CLF) using a balanced fertilizer (20-10-20) is often used at the start. This should be in a ratio of 6N-1P-3P with 50 to 75% of the nitrogen in the nitrate form.



Fertility Ranges for Poinsettia Medium
Value Fresh medium During Production
pH 5.0-6.0 5.8-6.4
EC (SPE) 1.0-2.0 1.25-2.5
Nitrate 50-300 100-200
Ammonium 5-30 <20
Phosphorus 10-100 5-50
Potassium 50-300 100-200
Calcium 100-300 100-200
Magnesium 50-150 30-70
K:Ca:Mg 2:2-3:1


Tissue Analysis Levels for Poinsettias
Element Critical Normal Toxic
Nitrogen 3.5 % 4.0-6.0 % 7.3 %
Phosphorus 0.15 % 0.3-0.6 % 0.9 %
Potassium 1.0 % 1.5-3.5 % 4.0 %
Calcium 0.5 % 1.0-1.75 %
Magnesium 0.2 % 0.3-1.0 %
Sulfur 0.1-0.3 %
Sodium 0-0.4 % 0.5 %
Chloride 0-1.5 % 3.0 %
Copper 1 ppm 2-10 ppm
Zinc 20 ppm 25-60 ppm
Manganese 40 ppm 60-300 ppm 650 ppm
Iron 50 ppm 100-300 ppm
Boron 15 ppm 25-75 ppm 100 ppm
Molybdenum 0.5 ppm 1-5 ppm


The balanced fertilizer may be alternated with a 15-0-15 or a combination of calcium / potassium nitrate to supply the extra calcium needed by poinsettias. Additional magnesium may be supplied by applying Epsom salts (magnesium sulfate) at 1-3 lbs/100 gal. once a month. Epsom salts should not be mixed with other fertilizers. Poinsettias appear to have a higher than normal requirement for molybdenum. The addition of 0.1 ppm Mo to the liquid feed program is often used: 1) Stock solution - one ounce ammonium or sodium molybdate in 40 fl.oz. 2) apply 0.15 fl.oz. stock solution per 100 gal water. One fertilizer program:

> 20-10-20 at 400-300 ppm N for first 4-5 waterings. Alternate with 15-0-15 or Ca(NO3)2 + KNO3.

> Drop to 200-250 ppm N after 5th watering.

> Eliminate all ammonium sources after Oct. 15.

> Drop to 100-150 ppm N in November.

Its important that pH and soluble salts of each crops be tested and charted at least every two weeks. Soil tests should be sent to a lab about once a month. Generally it is desirable to reduce nutrition in the last few weeks of the crop. In November and December, temperatures and light intensity are dropping and the needs of the plant decrease as flowers develop. Many growers will stop fertilizing completely in late November. Shelf life of poinsettias is increased if the media soluble salts is close to zero at shipping time.

Pinching

Pinching is the removal of the terminal growing point to stimulate the growth of lateral buds. Pinch poinsettias by removing the growing point plus one maturing leaf. The topmost one or two maturing should also be removed to get more uniform lateral bud development. Specification may be set by the grower or the market to have a certain number of flowers per pot. This can be controlled by how many nodes are left on the rooted cutting after the pinch. If a 6" pot should have 4-5 flowers at maturity, leave 5-6 nodes on the cutting after the pinch. Usually the lower 1-2 nodes will not develop lateral shoots sufficiently to contribute flowers. It is most important to pinch according to schedule and on-time!



Leaf Number Specifications at Flower Initiation
Pot Size Leaf Number Finish Height
4.0 0 8-10"
4.5 0-1 9-12"
5.5 2-3 11-13"
6.0 3-4 14-16"
6.5 4-6 15-17"
7.0 5-7 15-18"


Spacing

Poinsettia plants are often maintained on benches, pot-to-pot after potting and up to the time of pinch for easy maintenance and to make the pinching task easier. However, they should be placed at the final spacing soon after pinching and before plants begin to crowd. This increases the light interception by the plants and decreases the need for growth retardant.



Final Spacing for Pinched Plants
Pot size Cuttings/pot Spacing (") Sq.ft./pot
8 3 19 19 2.5
7 2 17 17 2.0
6 2 15 15 1.5
6 1 14 14 1.3
5 1 12 12 1.0
4 1 8 9 0.5


Environment

Temperature

The rate of growth in poinsettia is primarily influenced by the daily average temperature. The base temperature for leaf unfolding is 41 to 48F. Leaf unfolding rate increases above the base to a maximum of one leaf every 4-5 days at an average of 77F. Leaf unfolding rate above 77F decreases until plant death occurs at about 95F. Temperature can thus be used to control leaf unfolding rate. During the vegetative stage of growth, night temperatures may be 65-70F and during the day, 70-78F. However, one way to achieve consistent crops from year-to-year is to have the same number of leaves per shoot at the time of floral initiation. This can be achieved by manipulating temperature during the vegetative stage.

Night temperature should be reduced at the time of floral initiation to 68-70F, above 73F delays flowering. This generally occurs late September to early October. Bract development and final size is influenced by average temperature. For maximum bract size, maintain 68F for 3-4 weeks after bract color starts to appear. It is desirable at this point to reduce the night temperature further the last 2-3 weeks to 62F night temperature to improve bract coloration and prevent premature cyathia abscission.

DIF can be used as an effective tool to control poinsettia height. It is most effective when internodes are rapidly elongating during the first 3-4 weeks after the pinch. A negative DIF can be used to make plants more compact. An early morning dip or rise (6F) in temperature can also be used to increase or decrease height.

Light Intensity

Poinsettias should be grown where they receive maximum light intensity (5000-6000 ft.ca.) as long as temperatures can be controlled. Shading may be necessary to control temperature early in the crop as cuttings are establishing.

Photoperiod

The poinsettia is a qualitative short-day plant for floral initiation with a critical photoperiod of 12 to 12 hours when the night temperatures are less than 70F. However, a longer night or shorter day is required at high temperatures. The flower bud becomes microscopically visible after 7 tp 10 short days. In the northern hemisphere, the natural photoperiods become short enough for natural floral initiation between September 21 and 27. Most cultivars come into full flower about 8 to 10 weeks later, or late November to early December. The actual date of floral initiation depends on environmental conditions. Cloudy days and cool nights will result in earlier floral initiation, and bright, warm days will result in delayed floral initiation.

It was not necessary to manipulate day-length until the market for poinsettias became earlier and earlier. Thanksgiving marketing of many poinsettia cultivars requires black cloth applications from mid-September to mid-October. Poinsettias may be forced at any time of the year using night-interruption lighting. This is accomplished by applying a minimum of 10 ft.ca. to plants from 10:00 PM to 2:00 AM to simulate long days. Conversely, short days may be simulated by pulling black-cloth to exclude light from 5:00 PM to 6:00 AM. Poinsettias must receive at least 6 weeks of uninterrupted short days for flower development to continue normally.

Poinsettia cultivars are classified into "response groups" according to the time required from the beginning of short days to flower. Response groups are indicative of how long a cultivar requires for flower development but the actual time can vary with the environment (see table).

Growth Retardants

A-Rest, B-Nine, Cycocel, Sumagic and Bonzi are all registered for controlling stem elongation in poinsettia.

A-Rest is applied as a spray at 50 ppm by applying 1 gallon to 200 sq.ft. It should be applied when the lateral shoots are 2-2" long. A second application can be made 2 weeks later if needed. A-Rest may also be applied as a drench at 0.25-0.5 mg a.i. per plant

Bonzi is applied as a spray at 50 ppm by applying 1 gallon to 200 sq.ft.. It should be applied when the lateral shoots are about 2" long. One application is usually all that is needed.

Cycocel is the most widely used growth retardant used on poinsettia. It is applied as a spray at 1500 ppm when the lateral shoots are 1-2" long. Cycocel may also be applied as a drench at 3000 ppm. Subsequent applications may be applied as needed every week up to and no later than October 15.

B-Nine + Cycocel tank mix has been found to be highly effective. The two together can be applied at 2500 ppm B-Nine plus 1500 ppm Cycocel when the lateral shoots are 1-2" long. Only one application should be used because of extreme effectiveness. This mix should not be applied after September 30. Thought B-Nine may be used alone as a spray at 2500 ppm, it has little effectiveness.

Sumagic may be applied as a spray at 2.5-15 ppm. However, this chemical has only recently received registration for use on poinsettias and growers have little experience with it. Use experimentally at first.

Scheduling

Under natural photoperiods, scheduling poinsettias centers around the natural date of floral initiation (September 21-27). As long as the day length is not altered artificially, each cultivar will flower 7 to 10 weeks after that date depending on its response group. Crops for different parts of the Thanksgiving/Christmas season can be finished at different times by growing different cultivars from different response groups and by modifying the night temperature. A cultivar can be finished in more time (usually not more than a week longer) than its response time by lowering the night temperature but it cannot be finished any faster.

The relative size of plants in different pot sizes is largely controlled by the amount of time from propagation to floral initiation. Thus, early season cutting go into large pots so they have the time to attain a large size before floral initiation. Conversely, late season cuttings go into small pots so they won't get too large before floral initiation.

The other major controlling factor is the timing of the pinch. Cutting should be pinched at a time relative to floral initiation so that the correct amount of growth occurs in proportion to the pot size. If a 4" pot is pinched to early, it will get too large before floral initiation. Conversely, if a 6" pot is pinched too late it will not get large enough before floral initiation to be in proportion to the container. This is why pinching must be done on time.