Eucalyptus

Eucalyptus are native of Australia. The term Eucalyptus oil denotes three distinct group of essential oils viz. medicinal-type, perfumery-type and phellandrene-rich type. Blue gum Eucalyptus globulus Labill belongs to the first group which has high cineole content and wide medicinal application. Eucalyptus citriodora Hook belongs to the second and third group which are characterized by their high citronellal and phellandrene content respectively.

E-globulus is a native to Tasmania and now, it is planted practically all over the world. In India, it was first introduced in 1843 in Nilgiris, now it is cultivated in the states of Tamil Nadu, Karnataka and Kerala. Eucalyptus globulus is also a good source of pulp wood and fuel.

E.citriodora is a large tree, often attaining a great height with a smooth whitish to pale pink bark. It is commonly called as citron scented gum or lemon grass scented gum. It can be easily identified by its characteristic fruit and lemon scented leaves. Two strains viz. Pubescent and glabrous type exist in E.citriodora and the former type is rich in oil content and oil quality. It is native of Queensland and is now grown in most of the hill stations of South India. The oil is widely used in soap, perfumery and cosmetic industries and for the isolation of `hydroxy citronellal’ used in the manufacture of high grade perfumes. The demand for the oil in our country is around 55 tonnes per annum.

Climate and Soil:

The plant is sensitive to severe frost and excessive drought. It tolerates rainfall upto 400 cm but can be grown in places receiving rainfall from 200 to 300 cm annually. E-globulus can grow well above 2000 m MSL but E.citriodora grows well from 1500 to 2000 m MSL. Higher the altitude, better is the quality of the oil. It can be grown in acidic soil, rich in organic matter, with good drainage.

Eucalyptus is propagated by seed. As the root system is sensitive to transplanting, the seeds are directly raised in polythene bags of 22 cm x 16cm size. The containers are filled with pulverised shola soils. Two seeds are sown in each bag and the right time of sowing is January/February under South Indian conditions. The polybags are staked in the nurseries and partial shade is provided. The seeds normally take 10-15 days for germination and they attain plantable size within 2 to 3 ½ months from sowing or when the plants have produced 5 to 6 true leaves.

The land is cleared of the vegetation and pits 30 x 30 x 45cm size are dug at spacing of 2m x 2m. The pits are then allowed to wither before planting. The pits are filled with topsoil after adding 30g of rock phosphate per pit. Right planting season is the commencement of South West monsoon and while planting, polythene bags are completely removed and planted without damaging the root system. Staking the plants to permit the wind damage is desirable. Gap filling is done until two years to ensure proper population in the field.

The Cinchona department in Tamil Nadu recommends 200g per plant a fertilizer mixture of Nitrogen, Phosphorus and Potash at 25: 38: 38. This fertilizer mixture is applied by pricking the soil to a depth of 8 cm during the end of monsoon season.

In E.citriodoro, harvesting consists of pruning and collecting the terminal branchlets and leaves upto three years. In the Fourth year, coppicing the main stem is done 5cm above the stem portion having lignin. The coppicing cycle is adopted for every fourth year and the leaves are collected for distillation. Recently, it has been reported that instead of harvesting at the end of coppicing cycle, harvesting the leaves at periodic intervals (6-12 months) results in higher leaf yield with higher citronellal content.

Another method of harvesting involves pollarding the main stem at a height of 3m and the leaves are regularly collected for distillation from the shoots that emerge from the pruned stems. Best time for harvest of the leaves is March-May as the leaves have high oil content at that time. In Wynad area, harvesting twice i.e. premonsoon period (May) and post monsoon (November) is recommended. The harvested leaves are dried in shade for one day and distilled. Steam distillation is preferred to other types of distillation. On an average, the leaves yield 1.0% oil. The oil is a rich source of citronellal (70 to 80%).

In the case of E-globulus leaves are collected from the trees by cutting the side twigs twice or thrice in a year or the fallen leaves are collected from the plantations for distillation. When the plantation is felled for pulp wood purpose also, available leaves will be collected for distillation. The leaves are distilled high throughout the year but the most favourable time for distillation is from April to September, because of the yield of oil and cineole content during this period.

The collected leaves are dried in shade for three days and then subjected to steam distillation. Distillation per charge takes 5 to 7 hours. The yield of essential oil ranges from 0.75 to 1.25 percent. As the crude oil is wet, coloured and contain lower aliphatic aldehydes of unwanted odours, it has to be rectified or purified. This rectification involves the treating the oil over anhydrous sodium sulphate and distilling over 1 to 2% caustic soda. The cineole content varies from 75 to 85%. The rectified oil is colourless and has an aromatic camphoroceous odour.