Climate and soil
The crop thrives well in regions which receive a well-distributed annual rainfall of 1500-2500 mm with a mean temperature of 15°C to 35°C, relative humidity of 75-90% and 600-1200 m above MSL. Cardamom grows luxuriantly in forest loam soils, which are generally acidic in nature with a pH range of 5.5-6.5. Growth of cardamom is enhanced, when planted in humus rich soils with low to medium available phosphorus and medium to high available potassium.
Released varieties/selections of cardamom with high yield potential and superior capsule characters from different research organizations are given in Table 1. Apart from these, farmers varieties like Njallani green gold, Vander cardamom, Panikulangara No. 1, Palakuzhi selection and Valley green bold are also grown in cardamom growing tracts of the country.
Propagation by vegetative means through suckers is considered to be the most preferred method. Production of planting materials from seeds and through tissue culture are alternative methods of propagation. Seedling propagated plants may not be true to its parent.
Establishment of clonal nursery is essential for large-scale multiplication of high yielding varieties/selections. The planting unit consists of a grown-up tiller with a portion of the rhizome and a developing shoot. Sucker multiplication can be taken up from the first week of March to September. The site selected should be in open, well-drained areas adjacent to a perennial water source. Trenches with a width and depth of 45 cm and convenient length are prepared and filled with humus rich top soil, sand and well decomposed compost. The planting units are planted at a spacing of 1.8 m x 0.6 m in the trenches. To protect the planting units from direct sunlight and desiccation, overhead shade/pandal need to be provided. For better establishment of the suckers, irrigation may be given once in a fortnight. Apply fertilizers @ 48:48:96 g NPK per sucker in 2-3 splits starting from two months after planting. Neem cake @ 100-150 g/ plant may also be applied alongwith the fertilizers. On an average, 15- 20 good quality planting units could be produced from a mother clump within ten months of planting.
Cardamom seedlings are raised in primary and secondary nurseries.
The nursery site is selected in open, well-drained areas, near a water source. Prepare the area by removing existing vegetation, stumps, stubbles and stones and dig to a depth of 30 cm. In the prepared area, beds of size 6 m x 1 m x 0.2 m are made and a thin layer of humus rich forest soil is uniformly spread over the beds. Fully ripened bold capsules from high yielding, disease-free mother clumps are collected from second and third harvests during the month of September. One kg fresh capsules comprising of about 500-800 fruits is sufficient to produce 3000-5000 seedlings. The seeds are extracted by gently pressing the capsules and then washed 3-4 times in cold water to remove the mucilage adhering to the seeds. The washed seeds are drained, mixed with wood ash and dried under shade. To ensure early and uniform germination, seeds should be sown immediately after extraction, preferably within 15 days since viability of the seed is lost during storage. The ideal season for sowing is September in Karnataka and November-January in Kerala and Tamil Nadu. Acid scarification with 25% nitric acid increases the germination percentage. For this, wrap the extracted seeds in nylon net, tie it loosely and then immerse in 25% nitric acid for 10 minutes. After treatment, the seeds are removed and washed repeatedly in cold water to remove traces of acid. Sow the seeds in rows spaced at 10 cm and 1-2 cm apart within the row. The seed rate for 6 m x 1 m sized bed is 30-50 g. After sowing, the beds are covered with a thin layer of sand and mulched with grass or paddy straw to a thickness of 2 cm over which tree twigs are laid. Water the beds regularly to maintain sufficient moisture and to promote germination. Germination commences in about 20-25 days and may continue for a month or two. Once sprouting is observed, remove existing mulch and maintain thin mulch material between the rows. Protect the seedlings by providing overhead shade. Transplant the seedlings at 3-4 leaf stage to the secondary nursery.
Seedlings are raised in the secondary nursery by two methods.
• Bed nursery
The beds are prepared as described in primary nursery. Spread a layer of compost on the bed and mix thoroughly with soil. Seedlings with 3-4 leaves are transplanted at a distance of 20 to 25 cm. Mulching and watering should be done immediately after transplanting. In Kerala and Tamil Nadu, transplanting is carried out during June-July, whereas in Karnataka it is undertaken during the months of November-January. Apply 90:60:120 g NPK per bed of 6 m × 1 m size, in three equal splits at an interval of 45 days. First dose of fertilizer may be applied at 30 days after transplanting. Earthing up need to be undertaken after each fertilizer application and hand weeding is done once in 20-25 days. One month before uprooting, the shade should be removed to encourage better tillering. The seedlings will be ready for transplanting after 8-10 months of planting.
• Polybag nursery
Polythene bags of size 20 cm × 20 cm and 100 gauge thickness are filled with potting mixture consisting of forest top soil, cow dung and sand (ratio 3:1:1). Provide sufficient holes at the base of polybags to ensure good drainage. Seedlings at 3-4 leaf stages are transplanted into each bag (one seedling/bag). Seedlings raised in the polybags have a uniform growth and nursery period could be reduced by 5-6 months.
Nursery leaf spot
Leaf spot caused by the fungus Phyllosticta elettariae is a destructive disease in primary nurseries. It appears mostly during February-April with the receipt of summer showers. The disease manifests as small round or oval spots, which are dull white in colour. These spots later become necrotic and in the advanced stages, central portion of the spot withers off leading to the formation of shot hole. In secondary nurseries, another type of leaf spot caused by Cercospora zingiberi is observed. Symptoms are yellowish to reddish brown rectangular patches on the lamina which are almost parallel to the side veins.
• Sow the seeds in August-September, to ensure sufficient growth of seedlings, so that they develop tolerance to the disease.
• Avoid exposure to direct sunlight from top or sides.
• The practice of raising nurseries continuously on the same site may be avoided. Prophylactic spraying with fungicides such as mancozeb (0.2%) may be given. First spray is to be given during March-April, depending on the receipt of summer showers and subsequent sprays may be undertaken at fortnightly intervals. Depending on the severity of the disease, two to three rounds of spraying may be given.
• Spraying mancozeb (0.2%) effectively controls leaf spot disease in secondary nurseries also.
Nursery leaf rot
Nursery leaf rot is caused by fungi such as Fusarium and Alternaria. This disease commonly appears on three to four months old young seedlings. The symptoms develop as water soaked lesions on the foliage, which later turns to necrotic patches leading to the decay of affected areas. Usually the leaf tip and distal portions are damaged. In severe cases, rotting extends to the petiole and leaf sheaths also. Avoid excessive watering to the seedlings and spraying carbendazim (0.2%) twice at 15 days interval after removal of the infected leaf portions manages the disease effectively.
Damping off or seedling rot
The disease appears in primary nurseries during rainy season and when there is excessive soil moisture due to inadequate drainage. As a result, the infected seedlings die and collapse in masses. In nurseries, the disease incidence varies from 10-60%. The disease is caused by soilborne pathogens such as Pythium vexans and Rhizoctonia solani. Fusarium oxysporum also causes similar seedling rot resulting in wilting of the entire seedlings.
• In primary nurseries, thin sowing may be practiced to avoid overcrowding of seedlings.
• Adequate drainage facilities may be provided to prevent water stagnation.
• Maintain proper phytosanitary measures in the nurseries by removing infected and dead seedlings.
• When the initial symptoms are noticed, drench nursery beds with 0.2% copper oxychloride @ 3-5 liters/m2. Two to three rounds of drenching may be adopted at an interval of 15 days.
• Pre-treatment of seeds with Trichoderma or Pseudomonas before sowing reduces the chance of early incidence of the disease in nurseries. Further, application of Trichoderma to the nursery bed @ 100 g/m2 (talc formulation with 106 cfu/g) reduces subsequent disease spread.