Commercial Greenhouse Production
Scientific Name: Dendranthema × grandiflora
Common Name: Pot Mum
Dr. J. Raymond Kessler, Jr.
The Florists' potted chrysanthemum is a complex hybrid composed of crosses among several annual and perennial species native to China. Though grown by the Chinese for over 2000 years, cultivars were not available in Europe until the 1800s. In the United States around 1889, Elmer D. Smith hybridized and named over 500 cultivars. However, real development of the chrysanthemum as a pot crop has occurred since the 1940's. The chrysanthemum used in pot culture today is a hardy or semi-hardy herbaceous perennial with flowers in a wide range of colors.
The chrysanthemum is a composite inflorescence with the individual flowers borne on a flat or convex receptacle called a capitulum. The capitulum is surrounded by an involucre of bracts. A single flower head has one or more outside rows of ray flowers, which are pistillate and a center (brown or green "eye") composed of disk flowers, which are dioecious.
Chrysanthemum are available in a wide range of flower colors, flower types, and plant sizes. Of these, some are more suited for cut flower production and others for outdoor planting, often called Hardy mums or Fall mums. However, about 100 cultivars are suited for and widely grown today as flowering pot plants. Cultivars suitable for pot culture today must exhibit the following characteristics: 1) form a well-shaped plant, 2) branch readily, 3) flower quickly on relatively short stems, and 4) have flowers in the desired shape, size, and color.
Chrysanthemum cultivars can be classified in at least three ways: 1) based on flower form, 2) based on cultural type, 3) based on height, and 4) based on response to photoperiod.
1) Singles - composed of one or two rows of outer ray flowers surrounding a tight group of short disk flowers with inconspicuous petals. This is the typical "daisy" form.
2) Quilled - similar to the single except the petals are narrow at the base and flair toward the end to form a "spoon" shape.
3) Anemones - similar to the single form except the disk flowers have more conspicuous, elongated and tubular petals forming a cushion.
4) Spider - similar to the anemone except the petals of the ray and disk flowers are long and tubular.
5) Pompons - a globular head formed by many short ray flowers of about equal length that cover the disk flowers so they are not apparent. Small pompon types are called "buttons".
5) Decoratives - the head is composed of many ray flowers that cover the disk flowers, but the outer rows are longer than the inner rows so the inflorescence in more float and open.
6) Large Flowered - this is a catch-all group composed of flowers of many forms but all must be larger than 4" in diameter.
This classification is based on how the cultivars are handled in production.
1) Standards - these types are usually grown single stem with all the lateral flower buds removed to develop one large, terminal flower head. This is usually used for cut flower production.
2) Disbuds - these types are usually grown multi-stem (plants are pinched as rooted cuttings) with the lateral flower buds removed to develop one large, terminal flower head on each lateral. This is usually use for pot crop production.
3) Sprays - these types are usually grown multi-stem with only the terminal flower bud removed to allow all lateral flower buds to flower. This is usually use for pot crop production.
Nearly all commercial pot chrysanthemum growers order either rooted or unrooted cuttings from specialists propagator/breeders. Stock production, thought common 20 years ago, is almost unheard-of today because of the difficulties and disease problems encountered. Specialists propagators maintain mother stock that is true to type, use culture-virus indexing to eliminate diseases, and grow and harvest large areas of stock to supply the market. So the propagation choice becomes 1) whether to purchase rooted or unrooted cuttings, then, if unrooted cuttings, 2) whether to direct stick in the final container or propagate in specialized cells, cubes, or trays.
Purchase Rooted Cuttings
Purchasing rooted cuttings from specialists propagators is probably the easiest method for small growers with no or limited propagation space. The cost per cutting may be higher than other methods and the grower has less control over cutting quality, but the only facilities required is an area of reduced light where the humidity can be raised with periodic mist (often by hand) for 2-3 days until root growth begins. Rooted cuttings from the propagator should be inspected upon arrival transplanted into final containers as soon as possible upon receipt. If this is not possible, the cuttings can be stored in a refrigerator at 33-40F for several days.
The propagation area should be isolated so the relative humidity can be maintained close to 100% and be large enough to accommodate about 3 weeks of production. Larger, unused areas make the environment more difficult to control.
Sanitation - the propagation should be constructed and equipped to keep everything that may come in contact with the cuttings disinfected. Bench surfaces and floors should be easy to clean and free of weeds.
Temperature - facilities should be available to keep the air temperature 70-85F. Heating in winter should not drop below 68F. Bottom heat to keep the propagation medium 70-74F dramatically speeds rooting.
Light - light intensities should be 3200-3800 ft.ca. Shading in the summer is usually needed not only to reduce the light intensity but to also control heat. Night-break incandescent lighting to simulate long days is mandatory. HID supplemental light is useful during low-light periods.
Mist - Uniform mist to keep cutting turgid during rooting is vital. Excessive mist will leach nutrients from the medium and leaves, over-saturate the medium reducing aeration, and stretch the cuttings. Inadequate mist causes wilting, necrotic leaf margins, and hard cuttings that do not root uniformly. Cuttings should never wilt! Thus, a continuous film of moisture should cover the leaves until roots form.
The frequency (how often the mist turns on) and duration (length of time the mist is on) of mist depends on many environmental factors and varies from season to season and throughout the day. This is usually controlled by programmable automatic systems such as an automatic mist controller. Mist nozzle capacity and spacing should be designed to provide uniform coverage over the propagation area. The mist duration should be long enough to cover the foliage with a film of water and depends on the capabilities of the system. The mist frequency depends on the environment, but a starting-point schedule appears above. Mist may be required at night to keep cuttings turgid during the first 3-4 days. Afterward, mist is applied from 1 hour before sunrise to 1 hour after sunset. Tests of the quality of the water supplied to the mist system should be done to determine alkalinity. High alkalinity can increase the pH of the propagation medium and cause chlorosis of the foliage during propagation.
Media - Almost any well-drained, course medium can be used to root chrysanthemums. This may be cells, flats, strips, or pots containing peat-lite media, rockwool, foams, or other artificial media. Cutting are usually stuck 1" apart in rows and 1-2" between rows.
Rooting Hormone - Rooting hormones containing IBA or NAA may not speed rooting but increase rooting uniformity. Liquids or talks containing 1500 ppm IBA should be applied to the lower -¼" of the cutting.
Growth Retardants - This is used on certain vigorous cultivars during warm times of the years to prevent stretch and produce a compact plant. Cutting are dipped into B-Nine at 1000 ppm and placed in plastic bags in a cooler overnight, then stuck the next morning.
Nutrition - Many growers begin fertilizing chrysanthemum cutting as soon as callus forms (4-7 days) using a balanced fertilizer at 200-250 ppm N. Some growers apply a dilute solution of potassium nitrate through the mist system for the first several days.
Many growers stick unrooted cuttings directly in the final container. The method reduces labor costs by eliminating the transplant step and can produce a more uniform product because root growth precedes unchecked. Production time is also often reduced. However, a larger, more controlled propagation area is required. Death of one cutting in a pot can ruin the marketability of a 6" pot. Also, cutting must be graded to the same size in each pot for a uniform final product.
Containers for direct sticking should be filled close to the top with medium and watered before sticking. One or two lower leaves should be removed from the base of the cuttings so they may be stuck ½-1" deep.
Many different combinations of media components are used in media for growing pot chrysanthemums. However, a media should be course, loose, and well drained with a high moisture holding capacity and cation exchange capacity. The pH of the medium should be adjusted to 5.7-6.2 using dolomitic limestone. Phosphorus is supplied using superphosphate and a micronutrient fertilizers is also mix in the media.
Rooted cuttings should be graded by size so that individual pots receive the same size cuttings. Unequal cutting size in the same pot inevitably results in and uneven pot at finishing. This can be compensated for only to a limited extent by pinching. Cuttings of a single may be graded into: 1) short - thin stem diameter and not well rooted, 2) average - medium stem diameter and fairly well rooted, and 3) tall - thick stem diameter and well rooted.
Cutting should be planted shallow with the roots just covered with medium. They are planted as close to the pot rim as possible and leaning out from the rim about 45. This allows the maximum space for lateral shoot development and light penetration. Cuttings should be planted in a moist medium and watered in twice soon after planting. The first watering should be clear water followed by a fertilizer solution.
Number of Cuttings per Pot
Chrysanthemums may be grown in pot sizes ranging from 3 to 7", but by far the most common size is the 6 or 6½". The next most common is the 4" pot. Each pot size requires a different number of cutting to produce an acceptable product. Six inch pots require 4 to 5 cuttings per pot in the late spring, summer, and early fall, 5 cuttings per pot are used at other times. Four inch pots always contain one cutting.
Newly transplanted cuttings should be placed pot-to-pot in an area of reduced light where the humidity can be raised with periodic mist (often by hand) for 2-3 days until root growth begins. The plants are often maintained pot-to-pot until the time of pinching. Pot-to-pot spacing conserves greenhouse space, helps maintain humidity around the plants, and minimizes the area required to provide long days.
Pot chrysanthemums require large quantities of fertilizer during the vegetative stage of production, especially nitrogen and potassium. It is vital that they be supplied ample nutrition beginning the day of potting. Many growers will water-in mums using 300-400 ppm N using a balanced fertilizer. This high rate may be applied at each watering until the roots reach the bottom of the pot, then the fertilizer rate is reduced to 200-250 ppm N on a constant liquid feed basis.
Benefits have been observed on pot chrysanthemums when liquid fertilization is combined with a slow-release fertilizer. Application of the slow-release fertilizer is more beneficial when applied to the media surface compared to mixing with the media. Slow-release fertilizer can be applied several days after potting. Follow the manufacturers recommendation for a rate. Liquid fertilization rates should be reduced in combination with slow-release fertilizers.
Soluble salts and pH should be monitored at least every two weeks during production. These readings can be charted to detect significant trends. The soluble salts for pot mums should be 1.5-2.0 mmhos/cm (2:1 extraction) but should not exceed 2.5. pH should remain in the range of 5.8-6.2 Soil and/or tissue test can be taken at least once per month.
Fertilizers high in ammonium (20-40% NH4) in the vegetative stage during the warmer periods of the year benefit rapid growth. However, the ammonium content should be reduced to <20% during cooler, low light periods of the year.
Fertilizer rates should generally be reduced once flower buds become visible to about 125-150 ppm N. Several studies have shown that post-production keeping quality is improved when fertilization is stopped all-together 3-4 weeks before finish or about the time of disbudding.
Pot chrysanthemums require plentiful amounts of water and fertilization. The media should be moist, or allowed to dry only slightly between waterings. Enough water should be applied at each watering to completely saturate the medium plus 10-15% leachate.
Manual watering cannot provide the degree of control over soil moisture required for quality pot mum culture and the cost in labor is high. Most good pot mum growers have the crops on some form of automatic watering system when placed at final spacing. Microtube systems are the traditional method. Other methods such as capillary mats and sub-irrigation are used successfully.
Potted chrysanthemums require the maximum light intensity (5000-6000 ft.ca.) available as long as temperature can be controlled. Growers in the south find it necessary to apply a 25-30% shade during the summer to control heat. However, these materials should be removed promptly in the fall. Generally, keep the greenhouse glazing material clean and replace old polyethylene as soon as light reductions are evident. Many growers will provide some additional spacing during the winter months.
Terminal buds of pot chrysanthemums are pinched to develop lateral branches and increase the number of flowers on the final product. Before pinching, several requirements must be met: 1) the plant must have a root system that has reached the bottom and sides of the pot, and 2) the development of 1½-1¾" of new growth on the cuttings, generally 12-14 days after planting. A soft pinch is used, removing about ½" of the stem tip, allowing 6-8 nodes to remain on the cutting. Hard pinches are not desirable because it reduces the number of breaks.
The application of methods to alter photoperiod and control the vegetative and reproductive state of chrysanthemum revolutionized the culture and marketing of pot mums during the 1940's and 1950's. Previously, chrysanthemums were grown only during a narrow time frame in the fall to take advantage of a natural change in photoperiod. Today, pot mums can be precisely forced into bloom each week throughout the year.
The chrysanthemum is a qualitative short-day plant with respect to flowering with temperature modifying the photoperiodic response. Plants flower when the day-length is shorter than the critical day-length and grow vegetatively when the day-length is longer than the critical day-length. However, chrysanthemums have two critical photoperiods, one for floral initiation and a different one for flower development. However, there is no single critical photoperiod because it can vary depending on the cultivar and temperature.
|Critical Daylength Based on Response Group|
|Critical Daylength (hrs/day)|
|Cultivar||Response group (wk)||Floral initiation||Flower development|
|'White Wonder'||6||16 hr||13 hr 45 min|
|'Pristine'||8||15 hr 15 min||13 hr|
|'Encore'||10||14 hr 30 min||13 hr|
|'Fortune'||12||13 hr||12 hr|
|'Snow'||15||11 hr||10 hr|
Chrysanthemum cultivars are often classified in terms of response group based on the time required from the beginning of short-days to flower ( to ¾ open). Most of the cultivars grown as pot mums are in the 8, 9, or 10 week response groups. A relationship generally exists between response group and the critical photoperiod. The shorter the response group time, the shorter the critical night length required for floral initiation (longer critical photoperiod). Conversely, the longer the response group time, the longer the critical night length required for floral initiation (shorter critical photoperiod).
The usual photoperiodic sequence for producing pot mums is to provide long days for vegetative growth followed by short days for flowering. The amount of time that the plants are provided long days determines the vegetative size of the plants at floral initiation and ultimately influences how big the plants will be at the finish.
Long days for vegetative growth are maintained throughout propagation, early growth, pinch, and until the lateral are about 1-1½" long, however, this may vary with the pot size and response group. Though not absolutely necessary, most growers used night-interrupted lighting during these stages throughout the year. Night-interruption lighting is usually started at 10:00 PM. Cyclic light is also used in large greenhouse ranges to conserve electricity. Use the following recommendations for facilities: For benches 48" wide, 60-watt bulbs with reflectors spaced 3 feet apart and 24-36" above the tops of the plants, 100-watt bulbs can be spaced 6 feet apart. Provide 1¼ watts per 3 sq.ft. A light meter should be used to ensure that at least 10 ft.ca. of incandescent light is received over the entire growing surface.
Night-interruption Lighting for Chrysanthemum
|Month||Hours / night|
Supplemental light from HID lamps to improve vegetative growth is often used during low-light period in the winter. HID lighting is supplied for 16 to 24 hours per day. Night-interrupted lighting is not needed when HID lighting is provided. Most growers apply HID lighting in the propagation area.
Artificial short days must be supplied to chrysanthemum during long-day times of the year, from March 21 to September 21 to ensure flower initiation and development. This is accomplished by pulling opaque material (black cloth) over the plants for 12-15 hours per day. It is convenient to perform this task from 5:00 PM to 8:00 AM from a labor point of view. However, in the south, excess heat can build up under the black cloth in the afternoon. Temperatures in excess of 85F can delay flower initiation and development, called Heat Delay. Under these circumstances, black cloth must be pulled later in the evening (7:00 PM) and remain over the plants later in the morning. Automatic black cloth systems have been developed and are used by many growers. These systems can be programed to apply shade at the proper time. Black cloth should be applied every day (including weekends) from the scheduled beginning of short days until flower buds begin showing color.
The primary goal during long days (vegetative period) is to develop plant size. In chrysanthemum, leaf unfolding rate increases linearly with an increase in temperature up to about 68F, levels off, then declines above about 75F. Therefore, the optimum temperature range for growth is 68 to 75F.
The optimum temperature for flowering generally declines from the beginning of short days to open flower. The optimum temperatures from the beginning of short days to visible flower bud is 68-72F night and day. Temperatures above and below 68-72F will delay flowering. After visible bud, optimum temperatures decrease to 65F to about the "showing color" stage and to 60F for the last two weeks. Temperatures below 60F will delay flower development. The optimum temperatures for flower development is lower than for many other crops. Therefore, chrysanthemum crops should have a dedicated finishing area for temperature control.
Chrysanthemum benefit from the application of supplemental carbon dioxide during the vegetative period with increased dry weight, increased lateral branching, larger leaf area, and shorter production times. Growers who utilizer supplemental carbon dioxide apply it mostly during propagation and the early vegetative period at 800-1000 ppm.
Disbud and Spray
The purpose of disbudding is to remove all lateral flower buds from each main stem on a pot to redirect the resources of the plant into developing a large, high-quality terminal flower. Disbudding should be performed as soon as the lateral buds are large enough to 'roll out' without damage to the terminal bud. At this time, the tissues are soft enough that the task goes quickly. If disbudding is not performed on time, the lateral buds become 'woody' and becomes difficult to remove, requiring more labor. Delayed disbudding also increases the change of breaking the stem, thus ruining the product.
The operation required for those cultivars grown as sprays (typically decorative and daisies) involves removal of the terminal flower bud (called Central Bud Removal) to allow lateral flower buds to develop. This operation should be performed as soon as the peduncle supporting the terminal bud begins to elongate and the terminal bud can be removed without damaging the lateral buds. Unfortunately, central bud removal can often result in a "clubby" appearance to the pot for certain cultivars.
One way to overcome the "clubbiness" on certain cultivars is to use Multiple Bud Removal. Multiple bud removal involves a second pinch to lateral buds that arise from the first pinch performed under vegetative conditions. This second pinch is usually performed about three weeks after the first or when the lateral shoots from the first pinch have a minimum of four, but not more than six leaves. Normally, this second pinch will be performed after the start of short days but before flower buds are visible.
The ideal pot mum is about 2-2½ times the height of the pot. To some extent, this can be controlled by the amount of growth (time from pinch to begin SD) which is allowed to occur under long days.
B-Nine (Daminozide) was one of the first growth retardants developed for controlling plant height of chrysanthemum and is still probably the most widely used. B-Nine is applied at 2500-5000 ppm (depending on the cultivar) when the lateral shoots from the pinch are 1½-2" long. A second or third application may be needed depending on the cultivar and time of year. A-Rest, Bonzi, and Sumagic is also labeled for chrysanthemum.
Differences in the rate of growth among chrysanthemum cultivars has lead to their classification into short, medium, and tall groups. Response group combined with height group has a large effect on how a given cultivar is scheduled. In order to achieve the ideal plant height in a 6" pot, cultivars in the short group are given 3 weeks of long days, those in the medium group are given 2 weeks of long days, and those in the tall group are given 1 week of long days after the pinch. This allows longer for growth to occur on the short cultivars and less time for growth to occur on the tall cultivars so that short, medium, and tall cultivars finish at about the same height.
Creating a Schedule
1) Determine finish (flowering) date.
2) Establish total crop time: response time + height time + propagation time.
3) Count back the total crop time.
4) Count forward 2 weeks for rooting cutting in propagation to determine potting date.
5) Count forward the number of weeks required for the height group to determine the pinch date.
Cultivar 1: 8 wk / medium. 8 (response) wks + 2 (height) wks + 2 (rooting) wks = 12 wks
Cultivar 2: 9 wk / short. 9 (response) wks + 3 (height) wks + 2 (rooting) wks = 14 wks
Cultivar 3: 10 wk / tall. 10 (response) wks + 1 (height) wks + 2 (rooting) wks = 13 wks
|Finish Mothers Day: May 12, 1996|
|Cultivar||Stick cutting||Pot rooted cutting||Pinch||Long days||Short days||Finish|
|C1||Feb 18||Mar 3||Mar 17||Feb 18 - Mar 17||Mar 17 -||May 12|
|C2||Feb 4||Feb 18||Mar 10||Feb 4 - Mar 10||Mar 10 -||May 12|
|C3||Feb 11||Feb 25||Mar 3||Feb 11 - Mar 3||Mar 3 -||May 12|
The list of insects that infest chrysanthemum is almost endless. At one time or another aphids, chrysanthemum midge, cyclamen mites, fungus gnats, leaf minor larva, mealybugs, nematodes, sowbugs, spider mites, spittle bugs, thrips, and various worms have been problems.
Diseases that infect chrysanthemum include Rhizoctonia, Pythium, cottony stem blight, ray blight, Botrytis, powdery mildew, septoria leaf spot, Verticillium wilt, Fusarium wilt, and several bacterial and viral diseases.