Introduction
Clove of commerce is aromatic, dry, fully-grown, but unopened flower buds of clove (Syzygium aromaticum) tree. Besides clove, clove oil obtained from buds stems and leaves, and oleoresin from buds and stems also have commercial value. The essential oil of clove is rich in eugenol, which has medicinal values.
It was introduced into India around 1800 AD by the East Indian Company in their spice garden in Courtallam, Tamil Nadu. From there, its cultivation extended to high ranges of Nagercoil in the Kanyakumari district of Tamil Nadu, Thiruvananthapuram, and Kollam to the Mekkara hills in Thirunelveli district. At present, important clove-growing states are Kerala (Quilon, Trivandrum, Calicut, Kottayam districts), Tamil Nadu (Nilgiris, Nagercoil, Ramanathapuram, Tirunelveli and Kanyakumari districts), Karnataka (South Kanara district), Maharashtra (Ratnagiri district), and Andamans.
Indonesia is a major producer of cloves with a share of 60% in global production. UAE, Japan, UK, Singapore, Kuwait, Saudi Arabia, Vietnam, USA, India, West Germany, and France are major importing countries. The area and production of cloves in India are estimated at 2,380 ha.
Clove is an important spice used all over the world for its flavor and medicinal values. The food processing industry uses both whole and ground forms of cloves in various preparations. Clove oil is used in perfumeries, pharmaceuticals, and flavoring industries. Clove oleoresin is used in the food processing industry.
Climate and soil
Clove requires a warm humid climate having a temperature of 20-30°C. It thrives well in areas receiving a well-distributed annual rainfall of 150-300 cm. In India, clove grows up to 1500 m above sea level and also in areas having proximity to the sea. A cooler climate with well-distributed rainfall is ideal for flowering. Hot summer or very cold winters are not ideal for clove as it does not flower under such conditions.
Clover grows well in rich loamy soils of humid tropics and can be grown successfully in red soils. The site selected for the cultivation of clove needs good drainage since its crop cannot withstand waterlogged conditions. Sandy soil is not suitable.
Varieties
There are no distinct varieties in clove. However, a high-yielding clove selection, SA-3 (PP CL-1), was proposed for release as a state variable. Clove plantations in India are reported to have originated from a few seedlings obtained originally from Mauritius and hence much variability is not seen in population mainly due to self-pollination in its crop.
Usually, three types of clove trees are seen: trees having pale red color flower buds, trees having small flowers turning red on maturity, and trees producing light red color normal buds. Commercially three types of cloves are known, viz. Penang, Zanzibar, and Madagascar clove respectively. In Indian gardens, occasionally trees producing larger cloves (king cloves) occur. Dwarf-type clove trees also occur occasionally.
Propagation
Seed propagation is commercially practiced in cloves. High-yielding trees are selected and marked during the flowering season. Seeds are collected from high-yielding trees for propagation. The seeds become available from June to October. To raise seedlings, seeds should be collected from fully ripe fruits. Fruits for seed collection, popularly known as the mother of clove are allowed to ripe on the tree itself and drop down naturally. Such fruits are collected from the ground and sown directly in a nursery or soaked in water overnight and pericarp removed before sowing.
The second method gives a quicker and higher percentage of germination. Only fully-developed and uniform-size seeds which show signs of germination by the presence of pink radicals are used for sowing. Though ripe fruits can be stored for a few days by spreading them in a cool shaded place, it is advisable to sow the seeds immediately after harvest. The seeds lose their viability if stored for a long time after harvesting.
Nursery practices
Beds for sowing seeds should be prepared of 15-20 cm height, 1 m width, and convenient length. The beds should be made of a loose soil-sand mixture over which a layer of sand may be spread (about 5-8 cm thick). Seeds can also be sown in sand beds at 2-3. cm spacing and depth of about 2 cm. But care should be taken to prevent the leaching of beds in rain. The seedbeds have to be protected from direct sunlight. If only small quantities of seeds are available for sowing, they can be sown directly in polybags filled with a mixture of soil, sand, and cow dung and should be kept in a shady cool place. The germination commences in 10-15 days. and may last for about 40 days.
The germinated seedlings are transplanted in polythene bags (25 cm x 15 cm) containing a mixture of soil, sand, and well-decomposed cow dung (3:3:1). Sometimes, seedlings are again transplanted after 1 year to large polythene bags containing the same soil mixture. The seedlings are ready for transplanting infield when they are 18-24 months old. Transplanting time can be reduced to 1 year by planting clove seedlings in a mixture consisting of soil and vermicompost in 1:1 proportion. The nurseries are usually shaded and irrigated daily. To avoid damage by crickets, Chloropyriphos 0.05% may be drenched in the nursery.
Cultivation
Planting
Clove can be grown as a pure crop or as an intercrop in coconut, areca nut, or coffee plantation. The area selected for raising clove plantations is cleared of wild growth before monsoon and pits of 75 cm x 75 cm x 75 cm size are dug at a spacing of 7 m. Eastern and northeastern hill slopes, well-drained valleys, and river banks are ideal for clove. If planted as an intercrop, spacing has to be adjusted based on the spacing of the major crop.
The pits are partially filled with compost, green leaf, or cattle manure and covered with topsoil. The seedlings are transplanted in the main field during the beginning of the rainy season, in June-July, and in low-lying areas, towards the end of the monsoon, in September October. Clove prefers partial shade and comes up well at higher elevations, having well-distributed rainfall. In order to give a cool humid microclimate, intercropping with banana is ideal.
Training/Pruning
Training and pruning are not required in clove plantations. Pruning is not effective in inducing low branching and is not common in many areas. Occasional thinning, however, helps in preventing overcrowding of branches in full-grown trees. Diseased and dead shoots are systematically removed without injuring trees.
Nutrition
Clove trees are to be manured regularly. and judiciously for their proper growth and flowering. Cattle manure or compost @50 kg and bone meal or fish meal @ 2-5 kg per bearing tree per year can be applied. Organic manures can be applied as a single dose at the beginning of the rainy season in trenches dug around the trees. The application of inorganic fertilizers @ 20 g N (40 g urea), 18 g P₂O, (110 g superphosphate), and 50 g K₂O (80 g muriate of potash) in the initial stage is recommended. The dosage is progressively increased to 300g N (600 g urea), 250 g P2O2 (1,560 g superphosphate), and 750 g K₂O (1,250 g of muriate of potash) per year for a grown-up tree of 15 years or more. The fertilizers must be applied in two equal split doses in May-June and in September-October in shallow trenches dug around the plant normally about 1-1½ m away from the base. Mulching of trees with fallen leaves and application of river silt is also beneficial.
Irrigation
It is necessary for clove but waterlogging has to be avoided. Watering is essential in the initial stages in absence of rains. Irrigation should be given during the summer months. Applying 8-10 liters of water daily either through drip or through basin irrigation during January-May is essential for proper growth.
Aftercare
Provide shade for seedlings in the initial years. Weed the basins as and when necessary. Banana can be grown to provide shade during the initial establishment or even artificial shade regulation mechanisms can be adopted till the plant establishes. Mulching of plant basins with dried leaves or any other mulching material is an essential practice for clove cultivation. Weeding is also an important intercultural operation and must be carried as and when required to keep the field weed-free.
Diseases and pests
Diseases
Dieback: Drying of shoot from tip backward. Caused by a fungus, Cryptosporella eugenia, it can be controlled by and spraying of Mancozeb or Carbendazim.
Leaf spot and bud shedding: It is characterized by dark brown spots with a yellow halo on leaves. It is caused by Colletotrichum gloeosporioides. Such spots also appear on buds resulting in their shedding, C. crassipes causes reddish-brown spots on leaves. The dark brown lesion starts from leaf margins which later merge to form chocolate brown necrotic areas, resulting in drying up of branches.
Insect pests
Stem-borer: The stem-borer infests the main stems of young trees in the basal region. The larva of pest girdles stems and bores downward into it. The girdled portion and bore-hole are covered with a mat-like frass material. The infested trees wilt and succumb to pest attacks subsequently. Fully-grown larvae are creamy-white with a black head and measure about 8.5 cm in length. To control the damage caused by the pest. inspect the base of clove trees regularly for symptoms of pest attack. Spray quinalphos (0.1%) around the bore-hole and inject the same into the bore-hole after removing the frass. Swab the basal region of the main stem with carbaryl paste and keep the basins free of weeds.
Scale-insects: Many species of scale insects infest clove seedlings in nurseries and sometimes young plants in the field. The scale insects generally seen on clove include wax scale (Ceroplastes floridensis), shield scale (Pulvinaria psidii), masked scale (Mycetaspis personata), and soft scale (Kilifia acuminata). The scales are generally seen clustered together on tender stems and the lower surface of leaves. Scale insects feed on plant sap and cause yellow spots on leaves and wilting of shoots and the plants present a sickly appearance.
Harvesting and post-harvest management
For clove, not much research has been done on quality improvements. But for maintaining the export quality standards, farmers take precautions for producing quality products.
Clove trees start flowering from the fifth year of planting under good soil and management conditions. Flower buds are produced on young flush. It takes about 4-6 months for buds to become ready for harvesting. The flowering season varies from September to October in plains to December-January at high altitudes. The unopened buds are harvested when they are plump and round and as they turn from green to light pink. At this stage, they are less than 2 cm long. The opened flowers are not valued as a spice. Timely harvesting of flower buds is essential to maintain the quality of the cured product. Delay in picking also leads to the pollination of flowers and fruit development. Picking is done by hand by climbing the tree or using ladders. Bending of branches or knocking off of bud-clusters with sticks is not desirable, as rough handling of trees affects the yield during succeeding years.
A clove inflorescence contains on an average 12-20 flower buds. The flower buds are separated from clusters by hand and spread in the drying yard on mats for drying. It takes normally 4-5 days for drying. Cloves are generally dried in sun or in artificial dryers. The correct stage of drying is reached when the stem of the bud is dark brown and the rest of the bud lighter brown in color. Well-dried cloves become only about one-third the weight of fresh cloves. About 11,000-15,000 dried cloves make 1 kg. A 15-year-old tree gives an average of 6 kg fresh clove. The yield progressively increases as the age of the tree increases. The economic life of a clove tree is considered as 60-65 years. A high-yielding tree of 40 years, grown under ideal conditions and under proper management conditions gives an average yield of 60 kg.
In order to produce quality, produce care has to be taken to maintain hygienic conditions while drying, packing, and storing cloves. The cloves have to be dried immediately after harvest. Delayed drying causes fermentation and results in a poor-quality product. It is generally dried in sun or in artificial driers. The clove has to be raked and turned frequently for uniform drying. A well-dried product would have a dark brown color. It takes 4-5 days for drying. Good quality cloves should be whole, unbroken, and stalkless, and must not contain any woody, and brittle cloves, and should have a strong aroma and spicy odor, and characteristic flavor. The product should be free from living insects and molds, and practically free from dead insects, insect fragments, and rodent contamination. The pesticide residues and metallic contaminants in the product shall also not exceed the limits as prescribed in
the Prevention of Food Adulteration Act. The clove buds are dried and cleaned free of any extraneous matter before they are stored in air-tight, moisture-proof containers away from sunlight. The product has to be checked frequently for any damage or moisture inside the container. If moisture is observed, cloves have to be dried again to a moisture level of 10% and re-packed.
The storage room should be clean, dry, cool, and free from any pests. Strong smelling detergents, paints, etc. should not be stored along with clove as it would affect the aroma and flavor of clove.
Cloves, whole, and the ground shall be packed in clean, sound, and dry containers made of metal, glass, food-grade polymers, wood, or jute bags. The wooden boxes or jute bags shall be suitably lined with moisture-proof lining which does not impart any foreign smell to the product. The packing material shall be free from any fungal or insect infestation and should not impart any. foreign smell. Each container shall be securely closed and sealed.
