Tuberose (Rajanigandha) Cultivation: Bulbs, Soil, Fertiliser, Pests and Returns

February is the busiest month of the flower year at the wholesale market at Godkhali in Jashore's Jhikargacha upazila. In February 2020, UNB reported, growers there expected that month's sales to reach Tk 70-80 crore if the weather held, and tuberose, the white, night-scented rajanigandha, made up about a quarter of what the area grew.

This guide explains how tuberose is grown in Bangladesh: what the plant is, the single and double types, the climate and soil it needs, how the bulbs are planted, what research says about manure and fertiliser, the pests and diseases to watch for, and what a hectare cost and earned in a study by the Bangladesh Agricultural Research Institute (BARI). Every figure is given as its source states it.

Tuberose is a perennial plant that grows from underground tubers, which farmers in Bangladesh call bulbs (kanda). Its scientific name has long been Polianthes tuberosa. The stored version of this guide placed it in the family Amaryllidaceae, as older books did; botanists now place it in the family Asparagaceae, subfamily Agavoideae, and molecular studies have shown that Polianthes sits inside the larger genus Agave, so some references list it as Agave amica.

The plant is believed to be native to central and southern Mexico. It is no longer found in the wild, probably because it was domesticated by the Aztecs, and it is now grown in many tropical and temperate countries. Its leaves are dull green, about 1 to 1.5 feet long and slightly succulent. The flower spike can reach about 3 feet and carries pure white, waxy, tubular flowers that open into six segments and are strongly fragrant.

The Bengali name means "scent of the night": the flowers open towards evening and their fragrance is strongest after dark. In Bangladesh and India the flowers are used in garlands, bouquets, hair ornaments and wedding decorations, and a cut spike stays fresh in a vase for about 7 to 10 days. Its fragrance has been distilled for perfume since the 17th century, when the flower was first taken to Europe.

Indian researchers at the ICAR Central Coastal Agricultural Research Institute in Goa noted in 2019 that flowers of the single type are mainly used for essential oil extraction, loose flowers and garlands, and contain 0.08 to 0.14 percent concrete, the waxy extract used in high-grade perfumes. Double types are used mostly as cut flowers and for garden display.

Commercial flower growing was still young in Bangladesh. Banglapedia describes both amateur and commercial floriculture as being at a nascent stage, with demand for cut flowers, mainly rose, tuberose, orchid and gladiolus, rising slowly, and limited quantities of rose and tuberose exported to the Middle East and Europe. It lists tuberose of the 'single' and 'double' varieties among the cut flowers traded regularly on a commercial scale.

Official figures were small but growing. BARI economists, citing the Bangladesh Bureau of Statistics, put the country's flower area in 2008-09 at 520.64 hectares and production at 4,308 metric tons.

The heart of the trade is Godkhali union in Jhikargacha. According to Abdur Rahim, president of the Bangladesh Flower Society, flower cultivation there began in 1983 on just 30 decimals of land. Reports in 2020 gave very different sizes for the belt, depending on who was counting:

• In February 2020 the Bangladesh Flower Society put the area at over 3,500 hectares, with 8,000 to 10,000 growers in Jhikargacha and the Godkhali wholesale market supplying about 70 percent of the country's flowers (UNB, Financial Express).
• The same reports gave the crop mix in Jhikargacha as gladiolus 45 percent, tuberose 25 percent and rose 20 percent, with gerbera and other flowers making up the rest.
• In June 2020 UNB described flower growing across about 6,500 hectares in 65 villages of Jhikargacha and Sharsha upazilas, with Godkhali the country's largest wholesale flower market.
• In December 2020 the local agriculture officer told The Daily Star that about 600 hectares in six unions of Jhikargacha were under commercial flower cultivation, involving 7,000 farmers and one lakh farm hands.

Prices at Godkhali in December 2020, as growers told The Daily Star, were Tk 200 to Tk 250 for 100 tuberoses, and a bundle of tuberoses sold for Tk 50.

The trade also carried risk. During the 2020 coronavirus shutdown, growers could not sell flowers ahead of Pohela Boishakh; the Bangladesh Flower Society said the sector lost at least Tk 450 crore over six months, about Tk 100 crore of it in Godkhali, and Cyclone Amphan damaged all the flower gardens in Godkhali that year, according to the upazila agriculture officer quoted by UNB.

Growers sort tuberose by the size and petal arrangement of the flower. Three classes are found:

• Single: the petals form one row. The flowers are pure white and very fragrant.
• Semi-double: the petals are arranged in two or three rows.
• Double: there are more than three rows of petals. The petal edges carry a faint red tinge, and the flowers are less fragrant than the single type.

Both single and double types are grown in Bangladesh. When BARI economists surveyed 100 tuberose farmers in Jhikargacha (Jessore) and Chuadanga Sadar in January 2010, 88 percent grew the double type and 12 percent the single type; in Jessore the split was 85 to 15.

Abroad, named cultivars are common. The double-flowered 'The Pearl' has broader, darker leaves and shorter spikes, while 'Mexican Single' is less decorative but lasts longer as a cut flower. Tamil Nadu Agricultural University (TNAU) lists single cultivars such as Calcutta Single, Mexican Single, Phule Rajani and Prajwal, and double ones such as Calcutta Double, Pearl Double, Suvasini and Vaibhav.

Farmers in the BARI survey ranked the lack of high-yielding planting material as their second biggest problem, after the lack of technical knowledge about improved cultivation, and the researchers recommended that high-yielding tuberose seedlings be made available to farmers at the right time.

Tuberose likes warm, humid weather, which is why it is planted in the warm season in Bangladesh. TNAU describes tropical conditions with a temperature range of 28 to 30 degrees Celsius as suitable, and well-drained loamy soil with a pH of 6.5 to 7.5 as ideal. Loam rich in organic matter that does not hold standing water suits the crop. The plant needs about four months of warm weather from planting to flowering.

In the BARI survey every farmer prepared land with a power tiller, ploughing five times on average (six in Jessore, four in Chuadanga), and every farmer planted in lines. Planting ran from March to April, and flowers were picked from September to May.

Tuberose can be raised from seed, but in Bangladesh it is grown almost entirely from bulbs. An onion-like bulb forms at the base of each plant, and an old plant carries a clump of bulbs with the largest in the middle. Plants from bulbs keep all the traits of the mother plant and flower sooner. Through winter the bulbs lie dormant in the soil, and at the end of winter they are ready to plant.

Medium to large bulbs are chosen. Large bulbs give healthy plants that flower early; small bulbs give weak plants that flower late. TNAU's guidance for Tamil Nadu gives these planting figures:

• Bulbs of 25 to 30 grams are used.
• They are planted on the sides of ridges at a spacing of 45 x 20 cm and a depth of 2.5 cm, about 1,12,000 bulbs per hectare.
• Bulbs are planted about 30 days after they are lifted from the old crop.

TNAU's planting season (June to July) is for southern India; Jessore and Chuadanga farmers planted in March and April. Seasons and spacing for a particular field are best checked with the upazila agriculture office.

Tuberose needs a well-fed soil, but the evidence shows that more chemical fertiliser is not always better. The fertiliser doses in the stored version of this guide could not be traced to a published BARI, DAE or Krishi Tothyo Service recommendation, so they are replaced here by what research bodies reported.

BARI's 2010 survey recorded what Jessore and Chuadanga farmers actually applied per hectare: 6.53 tons of manure, and 274 kg of urea, 268 kg of TSP, 216 kg of MoP, 54 kg of gypsum and 7 kg of zinc sulphate. Its production analysis found that yield fell with less manure and with urea, TSP and MoP used above the recommended doses.

A trial by Bangladesh Agricultural University and the Bangladesh Institute of Nuclear Agriculture at Sutiakhali, Mymensingh, from April 2009 to March 2010, compared the recommended chemical dose of 400, 300, 300 and 100 kg per hectare of urea, TSP, MP and gypsum with organic manure plus half that chemical dose. Vermicompost at 5 tons, poultry litter at 20 tons or cowdung at 20 tons per hectare, each with half the chemical fertiliser, gave larger bulbs and more flowers than chemical fertiliser alone. Poultry manure gave the highest bulb and flower yields, followed by cowdung.

In India, TNAU quotes the Indian Institute of Horticultural Research (IIHR) recommendation of 25 tons of farmyard manure and NPK at 200:200:200 kg per hectare, with all the phosphorus and potassium at final land preparation and the nitrogen in three equal splits: at planting, and 60 and 90 days after planting. For micronutrients it advises a foliar spray of zinc sulphate 0.5 percent, ferrous sulphate 0.2 percent and boric acid 0.1 percent.

Because soils differ from field to field, a soil test and the upazila agriculture officer's advice remain the surest guide to the dose for a given plot.

Tuberose is a labour-intensive crop. In the BARI survey a hectare took 571 man-days of human labour, 250 from the family and 321 hired. Labour was the largest single cost, at 30 percent of the total.

On average, farmers weeded 10 times, irrigated 11 times and sprayed insecticide five times in the second-year crop. The production analysis found that more labour, better seedlings and irrigation all raised yield significantly.

The crop stays in the ground for more than one season. TNAU notes that a planting lasts up to two years and can be kept for a third with good management, and the BARI researchers surveyed second-year gardens because commercial harvesting starts in the second year.

Because tuberose is spread by bulbs, diseases travel with the planting material. Extension research at the University of Hawaii described the main problems of the crop:

• Foliar nematode (Aphelenchoides besseyi), which causes black, greasy streaks along the leaf midrib in wet, warm weather; badly hit leaves bend, wilt and dry.
• Root-knot nematode (Meloidogyne species), which swells and galls the roots, stunts the plant and yellows the leaf tips; it is carried in galled bulbs and infested soil.
• Stem rot (Sclerotium rolfsii), which makes the crown leaves collapse at soil level in warm, wet weather and covers the base with white cottony growth and small round bodies like cabbage seeds.
• Flower bud rot, a bacterial rot linked to an insect that lays eggs on the buds.
• Thrips, which in warm, wet weather mark the petals with yellow-brown spots until the flowers shrivel and turn rusty brown.

TNAU also lists thrips, aphids, root-knot nematode and basal or stem rot as the crop's main pests and diseases.

In the Hawaii trials, dormant bulbs dipped in hot water at 50 to 55 degrees Celsius for 10 to 20 minutes all survived, were freed of nematodes, and produced four flower stalks per hill against one on untreated bulbs. The researchers stressed that choosing clean, large bulbs with few disease signs mattered as much as the treatment.

This guide gives no pesticide doses. A grower who sees these signs should take a sample to the upazila agriculture officer or the sub-assistant agriculture officer of the union, who can identify the problem and advise an approved treatment.

For cut flowers, TNAU advises cutting the whole spike, leaving 4 to 6 cm at the base. For loose flowers and perfume extraction, single florets are picked as they begin to open, early in the morning before 8 am. It gives yields of 2 to 3 lakh spikes per hectare a year for cut flowers, or 14 to 15 tons of loose flowers per hectare.

BARI's survey gives a Bangladesh picture. Farmers in Jessore and Chuadanga harvested an average of 4,54,425 sticks per hectare and sold them at Tk 1.5 a stick. The key per-hectare figures were:

• Full cost Tk 2,00,761, of which the variable cost was Tk 1,29,283.
• Human labour 30 percent of cost, land use 23 percent, fertiliser 17 percent and irrigation 12 percent.
• Gross return Tk 6,81,637, gross margin Tk 5,52,354 and net return Tk 4,80,876.
• Benefit-cost ratio 3.39 on full cost and 5.27 on variable cost.

Tuberose cost 26 percent more to grow than banana and 12 percent more than papaya, the crops it competed with for the same land, but its net return was 65 percent higher than banana's and 71 percent higher than papaya's. Yields were higher in Jessore thanks to better land preparation and fertile soil, while net return was higher in Chuadanga, where costs were lower.

The researchers recommended high-yielding seedlings for farmers, training by government and non-government bodies, and better market infrastructure and transport, since the lack of efficient transport was the third problem the growers named.

A new grower can start with the upazila agriculture office of the Department of Agricultural Extension (DAE), which in the BARI study helped list the tuberose growers of Jhikargacha and Chuadanga. Its officers can advise on soil, planting material, fertiliser and pests for a particular field.

Research on flowers is done at BARI's Horticulture Research Centre in Gazipur, where Banglapedia notes that BARI opened a floriculture unit to promote commercial flower growing.

Photo: JDP90 (Joydeep) / Wikimedia Commons (CC BY-SA 3.0)

Sources: The Agro News (Staff Correspondent), Bangladesh Agricultural Research Institute (Haque and others, Bangladesh Journal of Agricultural Research, September 2012), Kabir and others, Journal of Environmental Science and Natural Resources (2011), Banglapedia (Floriculture), Tamil Nadu Agricultural University (TNAU Agritech Portal, Tuberose), ICAR Central Coastal Agricultural Research Institute (Journal of Horticultural Sciences, 2019), University of Hawaii Cooperative Extension Service (Circular 427, Diseases of Tuberose in Hawaii, 1968), Wikipedia (Tuberose, February 2022), UNB and Prothom Alo (9 February 2020, 17 June 2020), The Financial Express (7 February 2020), The Business Standard (5 August 2020), The Daily Star (8 December 2020)