Commercial Greenhouse Production
Scientific Name: Kalanchoe blossfeldiana Poelln.
Dr. J. Raymond Kessler, Jr.
Kalanchoe is a succulent that provides consumers with a durable flowering pot plant requiring very little maintenance in the home or office. For growers, they are an attractive pot crop because they can be predictably forced into flower and marketed any time of the year. Although they are a leading pot crop in Europe, especially Germany, Denmark, and Switzerland, Kalanchoes are not as popular in the United States and may be considered a minor though steady crop for the greenhouse industry. They may be marketed as a center piece, in dish gardens, as patio plants, or as novelty gifts.
Kalanchoe blossfeldiana is a glabrous, succulent herd or subshrub that may develop woody stems with age. It is native to Madagascar (between 12 and 25 latitude), a large island in the Indian Ocean off the southeast coast of Africa. The species is found growing in the south and southeast part of the island where semi-arid conditions exist with rainfall less than 10-15 inches per year. Xerophytic plants and scrub-land typifies the vegetation in the area. The genus name, Kalanchoe, was derived from the native name for a Chinese species. The species name, blossfeldiana, was given in honor of Robert Blossfeld, a German hybridizer who in 1932 introduced it in Potsdam from its native Madagascar.
Most of the early cultivars were propagated from seed which required as long as nine to ten months to flower. Seed had to be sown in March for a December finish. Many of the better seed propagated cultivars were developed by the Swiss and include 'Tom Thumb', 'Yellow Tom Thumb', 'Melody', 'Exotica', 'Vulcan', 'Tetra Vulcan', and 'Yellow Darling'. Yet, many of the seed cultivar were often too tall, too sensitive to heat for flower initiation, and were not uniform in growth rate, plant form, or flower color.
Increased acceptance of Kalanchoes has been partly due to the efforts of breeding programs to produce asexually propagated cultivars with better plant form, a broader range of colors, and more uniform flowering response. A primary source of asexually propagated cultivars in the U.S. today is Mikkelson, Inc. of Ashtabula, OH. Many flower colors are available from yellow, to orange, to red within plant series including Bonanza and Prestige.
The seed of Kalanchoe are extremely small ranging from one to 2.5 million seed per ounce. Seed should be sown in open flats on a well prepared, fine-textured medium that has been watered before sowing. The medium should have a pH of 6.0 to 6.5, and steam sterilized before sowing. A 1 peat : 1 sand or number four vermiculite works well. Sow the seed in rows and lightly press into the medium without a seed covering. After sowing, enclose the flats in a clear plastic bag or cover with glass and place in indirect but bright light. Germination requires about 10 days in light at 70F. Remove the bag or glass as soon as seedlings appear.
Seed sown in mid-March will make 4-inch flowering plants by December. A January sowing is necessary to produce five- or six-inch flowering plants. However, Kalanchoe is a qualitative short-day plant and a January sowing may expose seedling to inductive conditions pre-maturely. It has been reported that Kalanchoe has a brief juvenillity period (up to eight pairs of leaves) in which short-days cannot induce flowering. After that point, seedlings become photo-receptive. Therefore, it is wise to provide seedling with night-breaking lighting (minimum 10 foot-candles from 10:00 PM to 2:00 AM from incandescent lamps) until the end of March. Seedling should be large enough to transplant into 2½-inch pots seven weeks from sowing.
Most of the better cultivars available in the U.S. today are asexually propagated from terminal cuttings of named cultivars. The vast majority of kalanchoe growers order rooted or unrooted cuttings from specialists propagators. However, some larger growers produce stock plants for a continuous cutting supply.
If licensed to do so, cuttings for stock plants can be obtained from a specialists propagator and established in 6-inch or larger pots. Stock plants must always be kept under non-inductive, long-day conditions by applying night-break lighting. Many growers apply night-break lighting year round as insurance. Temperatures should be 65 to 68F at night and 72 to 75F during the day with a minimum of 4500 foot-candles of light. Stock plants should be kept free of insects and disease and should never suffer moisture stress. Watering should be done early in the day so that foliage dries before night. Microtube irrigation is strongly recommended. Shoots on stock plants should be pinched or cuttings taken when it is possible to leave two to three leaf pairs on the plants. Healthy stock should produce new cutting about once per month.
Terminal cuttings for propagation should be two- to three-inches long with two pairs of leaves. Leaves are removed from the lower one or two nodes. These lower nodes are inserted into the medium during sticking. No rooting hormone is needed. A good rooting medium consists of 1 peat : 1 perlite or sand. Tray sizes of 72-cells per flat or larger work well. If propagation space permits, some growers will direct stick cuttings into final containers to reduce labor costs.
Intermittent mist is used on cutting so that high light intensity can be maintained without the cuttings wilting. However, light shading may be required during the late spring, summer, and early fall. Mist frequencies of 5 seconds every 5 minutes during the summer or 5 seconds every 10 minutes during the winter have been recommended as a starting point. Rooting medium temperature should be 70F and bottom heat is beneficial. Night-break lighting should be continued during propagation. Reduce the mist frequency after about a week or when callus forms. Cutting should be established enough to transplant in 14 to 21 days from sticking.
Kalanchoes may be grown in 3, 4, 4½, 5, or 6-inch pots, although 4- and 6-inch pots are more common. One cutting per pot is used for 3, 4, and 4½-inch pots, 1-2 cuttings per 5-inch pots, or 1-3 cuttings per 6-inch pot. For the 5- and 6-inch pot sizes, the grower must compare the cost for extra cuttings per pot with the extra production time required for one cutting per pot. For example, one cutting per pot requires about 2-weeks longer than three cuttings per pot. This, of course will vary with the vigor of the cultivar, season, and market quality considerations.
Because Kalanchoes are succulents, the medium should be fast-draining, but with a high organic matter content. A 50% peat plus 50% aggregate material such as perlite works well. Superphosphate at 4.5 lbs/cu. yd. and micronutrients at the manufacturer recommended rate should be incorporated in the mix. Dolomitic limestone is added at a rate to raise the pH to 6.0-6.5. Kalanchoes are sensitive to zinc deficiency which may be aggravated by high phosphorus. In this pH range, zinc is highly available while phosphorus is available, but not excessively. When potting Kalanchoe cuttings, the top of the transplant root ball should be flush with the surface of the growing mix to avoid stem rot.
Pots may be kept pot-to-pot until the canopies begin to close or about the time that short-day treatments begin. The table below provides some guidelines for final spacing of Kalanchoes. However, these spacing may be varied depending on the season, number of cuttings per pot, projected market size, the length of the vegetative period, and the vigor and leaf size of the cultivar.
|Kalanchoe Final Spacing|
|4-inch||6 × 6"|
|4½-inch||7 × 7"|
|5-inch||9 × 9"|
|6-inch||10 × 10"|
Kalanchoes, by their nature, are relatively resistant to drought, but this does not mean to keep them dry in the greenhouse. They should not be allowed to wilt or become severely dry. Water should be applied according to the stage of growth and environmental conditions. The medium should become somewhat dry between thorough waterings. However, an extended period of wet, soggy soil can lead to stem and root rots. Fewer problems are encountered if Kalanchoes are grown on open benches, with good air circulation, and using a watering system that keeps the foliage dry, e.g. microtube irrigation.
Constant liquid fertilization (CLF) can begin when the roots reach the bottom and sides of the pot using 200 ppm N. 100 ppm P205, and 200 K2O (20-10-20). Many growers will alternate this with a calcium nitrate/potassium nitrate mix to supple the extra calcium needed by Kalanchoes. Use CLF until the plants are well-budded, then finish with clear water. Good results have been obtained by supplementing the feed program with slow-release fertilizer.
Older cultivars required a soft, terminal pinch to increase branching, decease plant size, and increase the number of flowering stems. However, cultivars available today are very self-branching and do not require a pinch from March to September. In fact, to do so increases the production time about two weeks. A soft pinch to remove just the shoot tip may be beneficial from October to February.
Kalanchoes generally require high light intensity (3500 to 4500 foot-candles) to grow compact and control height. Higher light intensity also results more total flowers than low light independent of photoperiod effects. Supplemental lighting may be used during low-light periods to increase growth during the vegetative period. However, light shade is often required from May to October to control high temperatures.
Kalanchoes can be manipulated to flower on a specific finish date, 52 weeks of the year much like pot mums. Kalanchoes are qualitative short-day plants for flowering with a critical photoperiod of 12½ hours depending on the cultivar. However, more rapid floral initiation occurs using a 10-hour photoperiod (optimum critical photoperiod); the daylength most often used commercially. Some Kalanchoe cultivar can minimally initiate flowers with as few as two consecutive short days; however, as the number of consecutive short days increases, the number of flowers initiated increases exponentially up to 14 to 21 short days. For commercial production, however, at least 42 short days (6 weeks) are recommended for complete induction of the wide variety of cultivars available. Flower buds are usually visible at the end of this period. Returning plants to long days once the short day treatment is completed has the added benefit of reducing elongation of the terminal cyme and producing a more compact plant.
To maintain stock plants or cuttings in a vegetative condition, night-interrupted lighting must be applied in the middle of the dark period from mid-September to late March according to the following schedule: 1-hour in September and March, 2-hours in October and February, 3-hours in November and January, and 4-hours in December. Lighting is provided by spacing 60 watt incandescent bulbs 3-feet above the plants and 4-feet between bulbs (to provide 10-20 foot-candles). Lights must be applied seven days per week.
Kalanchoes will initiate flower buds naturally from mid-October to mid-March in northern latitudes. If a crops is provided natural conditions in the fall, they will flower from late December into January depending on the response group. From March 15 to October 15, black cloth must be pulled over the plants for 14 hours per day, seven days a week for floral initiation. Because Kalanchoes are highly sensitive to light, the black cloth must be of the highest quality with no light leaks. Preferable a light fiber blend with an aluminized top to help prevent heat build-up under the cloth in the warmer seasons.
Kalanchoe cultivars fall into response groups that range from nine to 13 weeks from the beginning of short days to flower. However, unlike pot mums, Kalanchoes are not as easily programmed. Within a given response group, flowering is often longer in the winter than in the summer. This is believed to be the combined effect of differences in temperature and light intensity on flower development (see table). It is, therefore, important for a grower to keep records of response times for specific cultivars under different environmental conditions. Plant age can also have an impact on flowering time. Older plants tend to flower faster than younger plants.
|Response group of several Kalanchoe cultivars (Mikkelson).|
|Cultivar||Flower Color||Response group|
Optimum temperatures for growth of Kalanchoes during the vegetative stage are 65-68°F at night and 75-80°F during the day. Sixty-five degree nights are used during short-day treatment. Temperatures below 62°F or above 75°F during the dark period will delay flowering. This becomes a problem during the summer when temperature can easily exceed 75°F under black cloth causing "heat delay". Curiously, Kalanchoes are more sensitive to high night temperatures early in the dark period rather than later. Covering the plants after 7:00 PM and removing the cloth later in the morning can avoid much of the problem.
Kalanchoe cultivar vary in vigor. Some may grow tall and faster than others in the vegetative state while some may show more flower stalk elongation than others in the reproductive state. Therefore, cultivar selection is one way to control plant height.
The vegetative size of the plant at the time short days are started also affects final height. Generally 0 (summer) to 2 (winter) weeks of long days may be provided for vegetative growth in 4 or 4½ pots. Six-inch pots with one cutting per pot may require 3-4 weeks of long days while 6-inch pots with three cuttings may require only two weeks. Vegetative size at the beginning of short days may also be influenced by propagation date, pinching, and general growing conditions.
B-Nine is the main growth retardant used in Kalanchoe production. For 4- and 4½-inch pots, apply at 5000 ppm as a foliar spray 4 to 5 weeks after the start of short days during the winter. This will primarily control elongation of the flower stalk. In the summer, two or three applications may be needed at 3, 5, and possibly 7 weeks after the start of short days. For 6-inch pots in the winter, apply 5000 ppm as a foliar spray 5 weeks after the start of short days, and in summer, 3, 5, and possibly 7 weeks after the start of short days. Do not apply growth retardant any later than seven weeks after the start of short days or flowers may be stunted. Kalanchoes do respond to A-Rest as a drench at 0.50 mg active ingredient per 4-inch pot applied 2 weeks after the start of short days.
Scheduling of Kalanchoe crops is a bit more uncertain than some other photoperiodic plants because the response time varies from summer to winter. Otherwise, scheduling is carried out much the same way as pot mums (see figure).
The primary insect problems are mealy bugs, aphids, brown soft scale, cabbage loopers, and cut worms. Caution, Kalanchoes are sensitive to many pesticides (EC) which utilize xylene as a carrier. Wettable powder formulations are safer.
The primary disease problems are powdery mildew, Phytophthora, and pythium.
Oedema: The appearance of warty or corky spots on the leaves. This occurs under extended cool humid conditions when cell burst and then form callous under high turgor pressure.
Zinc deficiency: Causes bleached, small, distorted young leaves and damage to the apical meristem.