Tuberose as a Cut Flower

The intense, exotic, sweet fragrance of tuberose (Polianthes tuberosa) is so enticing the plant has been grown for centuries. This fragrance, which has been compared to that of gardenia and jasmine, is most intense at night as the one to two inch waxy, white flowers open at the top of tall stems. It is one of the few flowers that continues to release fragrance after being picked. Commonly thought to be native to Central America, it was already domesticated by the Mayans and Aztecs prior to the voyages of Columbus. It has never been found as a wild plant and is believed to be extinct in that form, surviving only as a cultivated plant. It is now cultivated throughout the world. Tuberose is often used in weddings and in Hawaiian leis or as a fragrant accent in a bouquet or wedding designs. Florists also use the individual flowers in the same manner as stephanotis. Once commonly used in casket arrangements as well as in weddings, the popularity of this intense fragrance waxes and wanes. In recent years, it is being used more often both as a single fragrance or as a top note in a perfume.

Most of the tuberose sold in the U. S. is grown in California or Mexico. Other production centers include India, China, France, and Kenya. The fragrant oil, almost all of which comes from India, is one of the most expensive of the fragrant oils used in perfumes at more than $2,000.00 per pound.Tuberose is an herbaceous perennial that forms a tuberous root. It is in the agave family and forms 18 inch linear leaves clustered at the soil line in a rosette, with a few extending up the flower spike. Plants are three to four feet tall when flowering. Tuberose is very sensitive to cold and requires lifting the tubers each year except in USDA hardiness zones 8-10. They are relatively free of pests plus easy to grow and propagate.

Cultivars

Tuberose has two flower types, single and double. The single type is often called “Mexican tuberose” or “Single” while the double-flowered type is sold as ‘The Pearl’ or ‘Double’ Although very few cultivars are available in the U.S., internationally several dozen cultivars are reported. The single-flowered or common tuberose is more popular in the U.S. as a cut flower, is easier to grow than the double flowered, and is more fragrant. Worldwide, the double forms are more popular for cut flowers.

Although the flowers are pure white, the flower buds may have a light pink blush when grown under cool conditions. The flower will be pure white upon opening. Tubers (bulbs) of the single and the double form are available through retail and wholesale bulb suppliers. There is intensive inter-species and cross-genera breeding research being conducted in Japan, Taiwan, India, and the U.S. to develop orange, yellow, pink, and lavender tuberose flowers for the cut flower market as well as dwarf types for garden use. At this time, the color and color intensity of these hybrids are not consistent and are affected by environmental conditions. Colored tuberoses are not yet commercially available in the U.S. Most of the Polianthes species and related genera with colored flowers are not fragrant.

Planting

Tuberose grows best in full sun and well-drained, fertile soil and thrives under hot, humid conditions. Plant with the nose of the tuber at soil level or not more than one inch deep. Soil temperature optimum is above 68F. The optimum crop temperature range is 77 to 86F. Planting into slightly moist soil helps rehydrate the dried tubers. When tubers are planted vertically with the growing tips up rather than horizontally, stems are longer with no reduction in stem diameter, and the number of florets increases contributing to a higher quality stem (Nazari et al., 2007). Plant spacing varies based on cultural practices and market, time between planting and lifting the tubers, whether clumps of tubers or individual tubers are planted, and many other factors. A general rule would be to allow one square foot per plant. Once planted, maintaining adequate soil moisture is important as plant dormancy is induced by drying the tubers. Care is needed not to overwater or saturate the soil prior to leaf emergence as root rot may develop. Tuberose can be raised in a high tunnel or greenhouse under high light intensities as well as in the field.

When plants were grown in an unheated high tunnel, researchers found that the time to flower was decreased by 10 days, the number of flowering stems increased 150%, and flower quality improved (Brundell et al., 1985). The use of other season-extension techniques such as row covers and black plastic mulch also will enable earlier production. In one study, when tuberose was planted three months earlier than normal under perforated low plastic tunnels on raised beds, flowering was 44 days earlier compared to tubers field planted at the same time early in the season and 34 days earlier than those planted at the normal time (Singh and Singh, 2006). For late-season harvests, a high tunnel, walk-in row covers, or a heated greenhouse is needed for frost protection. Flower quality declines as temperatures cool. For continuous harvest in areas with long growing seasons, sequential plantings at two-week intervals are made.

Dry tubers from storage are dormant and require six weeks at 68F to break this internal dormancy. After this time, tubers can be planted directly or pre-sprouted prior to planting. Pre-sprouting results in earlier flowering and can compound the positive effect of growing tuberose in a high tunnel or another season-extension technique. Pre-sprouting the tubers can increase the number of flowering stems by 50 percent. Several methods have been used to pre-sprout the tubers. These include placing them in moistened sawdust in flats covered with polyethylene and kept at 95F for 15 days; using potting mix in crates, covering the tops with about an inch of mix; placing them in a single layer and frequently misting to rehydrate the tubers and initiate growth; or simply applying warmth to the dormant tubers.

Support

In the home garden and many commercial crop situations, no additional support is needed for the flower spike. When a commercial cut flower crop is grown where winds occur frequently or when grown in sandy soil, a single layer of netting may increase the number of straight, marketable stems by reducing lodging.

Fertilization

Tuberose is considered a heavy feeder, with recommendations of pre-plant applications of 80 pounds per acres of actual nitrogen. If soil potassium is low, flowering may be delayed or flower quality may be poor. Moderate levels of phosphorous are recommended. Many sources recommend using an organic source for plant nutrients such as compost or manure which should be incorporated prior to planting. An application of additional fertilizer or compost four weeks after planting or when flower spikes first emerge, may increase the number and quality of flowering stems produced for the season. Foliar applications of nitrogen and potassium have also been beneficial. Tuberose tolerates a range of pH from 6.5 to 8.1.

Irrigation

It is important that tuberose plants are in soil that is well drained to prevent root rots. Plants should not experience water stress at any time. Once tubers sprout and leaves emerge, weekly irrigation is recommended.

Light

Full sun or high light intensity is best when plants are field grown but shading may improve quality in areas with intense sunlight or temperatures frequently above 86F. Polianthes is daylength neutral but vegetative and reproductive growth is advanced by about 10 days when exposed to 16-hr photoperiods. 

Temperatures

Plants need temperatures of at least 55F to form a flower spike and at least 67F for individual flowers to form. Best flower formation occurs when temperatures are moderately warm, not falling below 55F or above 86F. Warm, humid conditions are preferred. Plants become stressed when grown under low relative humidity. The use of antitranspirants has been beneficial under high temperature and high relative humidity conditions (Moftah and Al-Humaid, 2006).

Pests

The main insect pests are thrips and spider mites. There is rarely a foliar disease problem, although the flowers may be affected by Botrytis under cool temperatures. There are reports of various leaf spots and a virus but these are not often seen. Root and crown rots occur when the soil is poorly drained. When grown as a perennial crop in warm climates (zone 9 -10), the tuber and roots may rot if the winter dormant period is exceptionally wet. Tuberose can have 30 to 50 buds per spike when grown well

Harvesting

Plants will flower four to five months after planting in the field. Greenhouse forcing at 68F requires about 132 days for double cultivars with single cultivars flowering two to three weeks later. Flowering stems can be harvested when the first flower opens on the spike. For local markets, stems can be cut when more flowers are open; however, the earlier flowers will dry out as they senesce and these will need to be removed prior to sale. Stems should be straight with a well-developed floral spike. Harvest early in the morning when temperatures are cool and plants are well hydrated. Freshly cut stems have a vase life of approximately nine days. When stems are cut with few flowers open, they are often cut dry and later graded and bunched. If more of the spirally arranged flowers are open, flowers may be damaged when stems are bunched. For this reason, some growers for local markets harvest directly into clean buckets containing fresh water plus hydrating solution, or a sugar-containing floral solution, omitting bunching or sleeving the stems. Vase life will be optimum if stems are not cooled or stored. There are few estimates of production potential or yields in the U. S. Flower yield will vary with variety, plant density, tuber size at planting, time of planting, duration of harvest season, and crop management. One report from India indicated approximately 152,000 stems per acre during the first year of a two-year cropping cycle (Khushk and Mal, 2007).

Postharvest

Tuberose is not appreciably sensitive to ethylene and does not require treatment. Research has shown that a 24-hour pulse at room temperature in a solution of 20 to 30 percent sugar plus a biocide and hydrator will significantly improve vase life and opening of buds on the flower spikes. Having at least one open flower on the spike increases the uptake of floral solution and vase life. If flowers are cut dry, then graded and bunched, the stems should be re-cut and then placed immediately into the high sugar floral solution for the pulsing treatment to ensure bud opening. To make a 20% sucrose solution, add 1 ½ cups of white granulated sugar to one gallon of consumer-level commercial floral solution such as Chrysal #3 or Floralife Original. Stems should be straight with a well-developed floral spike. The Japanese cut flower industry standard for tuberose indicates a minimum stem length of 28 inches (70 cm) with at least 10 pairs of buds and flowers that open horizontally. In the U.S. tuberose are usually sold in 10-stem bunches with stem length of 24 to 36 inches. If packed dry, horizontally in boxes, they must be held at the proper temperature to avoid curvature. Optimum storage temperature for tuberose is 33F. When stems are stored at this temperature in a high-sugar solution, some buds will continue to develop and open in the cooler. Stems can be stored up to a week under optimum conditions, including a sucrose pulse, with no adverse effects on bud opening or floral quality. Vase life in floral solution ranges from about 9 to 14 days, with single flowers having a longer vase life. Each floret is open for three days and a stem can have as many as 50 florets.

Propagation

Dormancy is induced by restricting moisture to the roots and by cooler temperatures. In warm regions without frost, water restriction is used to trigger the cessation of growth. When flowering ceases, i.e., foliage begins to yellow in the fall or after the first frost, taper off watering. Lift rhizomes after foliage dies back, grade the tubers, and dry for a day or two in the shade. After drying, store the tubers covered in a dry medium such as peat or vermiculite at 40F in a ventilated area. If plants received frost, remove all foliar tissue prior to drying the tubers. In the spring, axillary rhizomes can be broken off. The remaining tubers should be allowed to callus for a day or two at room temperature before replanting. These offshoots are produced in abundance; 15 to 20 from each of the larger tubers each year. The larger rhizomes are replanted to produce flowering stems. A tuber diameter of 2.5 to 4.25 inches is needed to produce a flowering stem so the largest tubers should be used as planting stock. Each tuber flowers once from the terminal bud on the tuber (Brundell and Steenstra, 1977).

Offshoots (tuberlets) rapidly develop under good growing conditions and produce the subsequent flowering stems. When clumps of tubers are planted, more stems are produced compared to planting individual tubers but the flowering stems are not as long or strong and the number of florets is less than those produced by single tubers. Smaller tubers require one or two years before flowering size is reached so the smallest tubers should be removed when planting clumps of tubers (Brundell and Steenstra, 1985).

Tuberose can be overwintered in the ground as far north as zone 7 if the ground is mulched heavily in mid-October. If left in the ground in warmer areas, tuberose should be dug up and divided at least every three years to ensure vigorous production of flowering stems. When overwintered in the ground, plants will bloom in July and August.

Seed production is poor in the single-flowered types, and seed germination rates are very low. Plants are self-sterile. Thus, vegetative propagation from tubers is the most economical method of propagation. Methods to propagate tuberose by tissue culture have been successfully developed for use in research and breeding programs.

Tuberose as Fragrance

Although intensely fragrant, the tuberose contains relatively small amounts of its essential oil which is not stable under heat extraction. The flowers won’t stand up to the high temperature used in water extraction or steam distillation. The traditional method of extracting the essence of tuberose uses the process of enfleurage, which extracts the oil into a fat without the addition of heat. Vegetable or animal fats are layered with the flowers until permeated with the scent. The oils are then separated from the fat when it is melted or a solvent such alcohol or hexane is used to extract the essence from the fat and then evaporated, leaving the volatile oil. Enfleurage yields the best results with jasmine, tuberose, jonquil, lily of the valley, and mignonette. Technically, essential oils extracted using volatile solvents are called absolutes.

A newer method uses low pressure without heat and a recyclable solvent to extract the essential oil of tuberose and other heat-sensitive flowers. The low amount of oil in each flower and the slow, precise extraction methods required to preserve the fragrance contribute to the high price of pure tuberose oil.

Tuberose Lore

Tuberose represents sensuality and is used in aromatherapy for its ability to open the heart and calm the nerves, restoring joy, peace and harmony. It is also believed to protect the energy and personal boundaries of the person wearing it. Tuberose helps develop intuition and solve problems and strengthens emotional depth. In India, it is believed to open the crown chakra, thereby improving psychic powers. The legend of the tuberose in France warns that young girls should not breathe in its fragrance after dark for fear that it would put them in a romantic mood. Similarly, in India tuberose is renowned for its strong aphrodisiac powers, and according to some stories, unmarried girls are warned not to breathe in its perfume after dark. Tuberose is also said to amplify artistic inspiration by stimulating the creative right side of the brain. And it brings serenity to the mind and heart.


Resources

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Dole, John M. And Harold F. Wilkins. 2005. Floriculture: Principles and Species. 2nd edition. Prentice Hall. New Jersey.
Huang,K.-L., I. Miyajima, H. Okubo, T.-M. Shen, and T.-S. Huang. 2002. Breeding of Colored Tuberose (Polìanthes) and Cultural Experiments in Taiwan. Acta Hort. (ISHS) 570: 367-371.
Khushk, Ali Muhammed and Bhugro Mal. 2007. Commercial cultivation of tuberose. Pakistan Herald. Dawn Media Group. November 5, 2007 accessed at www.dawn.com/2007/11/05/ebr6.htm on Nov. 14, 2008.
Moftah, A. E. and A. I. Al-Humaid. 2006. Response of vegetative and reproductive parameters of water stressed tuberose plants to vapor gard and kaolin antitranspirants. J. King Saud Univ. 2:127-139.
Nazari, F., H. Farahmand, M. Khosh-Khui and H. Salehi. 2007. Effects of two planting methods on vegetative and reproductive characteristics of tuberose (Polianthes tuberosa L.). Adv. In Natural and Applied Sciences 1(1): 26-29.
Reid, Michael. 1996. Postharvest Handling Recommendations for Cut Tuberose. Perishables Handling Newsletter. Issue No. 88 Page 21. November 1996. Verified 13 Aug 2009 at http://ucce.ucdavis.edu/files/datastore/234-83.pdf
Reid, Michael. 2004. Produce Facts: Tuberose – Recommendations for Maintaining Postharvest Quality. Postharvest Technology Research & Information Center. Univ. of California Davis.
Shen, Tsai-mu, Rong-show Shen, Kuang-liang Huang, Bor-shium Du. 2003. Breeding of Dwarf Tuberose Polianthes tuberosa L. Acta Hort. (ISHS) 624:73-76
Shen, T. M., K. L. Huang, and T. S. Huang. 1987. Study of tuberose hybridization. Acta Hort. 205:71-74.
Singh, Krishan Pal and Mam C. Singh. 2006. Use of low plastic tunnel for advancing early flowering in tuberose. ICAR News 12(4):1-2. Indian Council of Agricultural Research, New Delhi, India.