Citronella
Citronella is the essential oil extracted from the leaves and stems of Cymbopogon nardus, a perennial aromatic grass in the Poaceae family, commonly known as citronella grass.[1] Native to tropical regions of Asia including India, Sri Lanka, and Southeast Asia, the plant grows in dense clumps up to 6 feet (1.8 m) in diameter, featuring long, narrow leaves that are ½–1 inch (1.3–2.5 cm) wide and up to 3 feet (0.9 m) long, with finely serrated edges and drooping tips.[2] When crushed, the leaves release a strong, fresh citrus-like fragrance, which is the hallmark of the oil produced through steam distillation.[2] The essential oil of citronella is a pale yellow to light brown liquid obtained by distilling the partly dried plant material, with major chemical constituents including citronellal (approximately 32–45%), geraniol (up to 26%), and citronellol (around 18%).[3] These compounds contribute to its volatile, lemony aroma and bioactive effects, distinguishing it from similar oils like lemongrass (from Cymbopogon citratus).[3] Cymbopogon nardus is closely related to Cymbopogon winterianus (Java citronella), a hybrid variant often used interchangeably for oil production due to higher yields, though both share similar profiles.[3] Citronella oil is most notably employed as a natural insect repellent, particularly effective against mosquitoes and other biting insects for up to 2–3 hours when applied topically or via diffusion, often enhanced by additives like vanillin.[1] Beyond repellency, it exhibits antifungal properties against pathogens such as Aspergillus niger and Candida albicans, antibacterial activity, and antioxidant effects, supporting its use in cosmetics, soaps, perfumes, and even food preservation applications like extending bread shelf life.[1][3] The plant itself is cultivated in tropical areas worldwide, including Indonesia, Brazil, and Guatemala, for both industrial extraction and ornamental gardening, though it requires full sun and well-drained soil to thrive.[2]Botany
Genus and Species
Citronella refers to certain species within the genus Cymbopogon, a group of about 55 tropical and subtropical perennial grasses in the Poaceae family, characterized by their aromatic foliage and clumping growth habit.[4] These plants typically form dense tufts with erect culms reaching 1 to 2 meters in height, featuring long, linear leaves that are 30 to 90 centimeters long and 0.5 to 1 centimeter wide, often with a rough texture and a strong lemony scent when crushed.[2][5] The leaves arise from a short rhizome, and the plants produce inflorescences consisting of paired spikelets on slender branches, though flowering is infrequent in cultivated specimens.[6] The primary species associated with citronella are Cymbopogon nardus (L.) Rendle, known as Sri Lankan or Ceylon citronella, native to southern India and Sri Lanka, and Cymbopogon winterianus Jowitt, known as Java citronella, which originated in Indonesia as a hybrid cultivar derived from C. nardus.[6][7] C. nardus yields approximately 0.5 to 1% essential oil by weight from its leaves, with a composition featuring 55 to 65% combined citronellal and geraniol, while C. winterianus offers a higher oil yield of 0.25 to 1.3% and elevated geraniol levels, often exceeding 30%, making it preferred for commercial production.[8][7] These differences in oil yield and geraniol content arise from genetic variations, with C. winterianus exhibiting a more robust growth and higher biomass accumulation.[9] A related species is Cymbopogon citratus (DC.) Stapf, commonly known as lemongrass or West Indian lemongrass, which shares the genus but is distinguished from citronella species by its morphology, including uniformly green pseudostems without the reddish bases seen in C. nardus, and its sterile nature that prevents seeding, unlike the potentially fertile citronella grasses.[10][11] While both are used in essential oil production, C. citratus is primarily valued for culinary and different aromatic applications, setting it apart taxonomically and in practical use from the citronella-focused species.[12] The term "citronella" originates from the French word citronnelle, a diminutive of citron meaning "lemon," coined in the mid-19th century to describe the plant's citrus-like fragrance reminiscent of a smaller or milder lemon scent.[13]Habitat and Cultivation
Citronella grass (Cymbopogon nardus), a perennial aromatic species, is native to tropical and subtropical regions of Southeast Asia, including countries such as India, Sri Lanka, Indonesia, and extending to areas like South Sudan and Vietnam. It thrives in humid, subtropical climates characterized by high humidity and annual rainfall ranging from 1,500 to 2,500 mm, often found in open woodlands, grasslands, and areas with Acacia and Combretum vegetation.[14][15] For optimal growth, citronella requires well-drained sandy loam soils rich in organic matter, with a pH range of 5.5 to 7.5, and temperatures between 20°C and 30°C to support vigorous development. It is propagated primarily through slips or stem cuttings, though seeds can also be used; slips are planted at a density of approximately 28,000 to 40,000 per hectare, typically at spacings of 60 cm x 45 cm or similar configurations to ensure adequate aeration and nutrient access.[16][17] Major producers of citronella as of 2025 include India, Indonesia, and China, where cultivation supports significant essential oil output through established agricultural systems. The crop reaches maturity for the first harvest 4 to 6 months after planting, with subsequent harvests occurring every 3 to 4 months by cutting the foliage at ground level, allowing for multiple cycles per year in suitable climates.[18][19][20] Cultivation faces challenges from pests such as nematodes, red spider mites, and sucking insects like aphids, as well as diseases including leaf blight caused by fungal pathogens. Sustainable practices, including intercropping with compatible crops like tea or legumes and crop rotation, help manage these issues while enhancing soil fertility and reducing chemical inputs.[21][22][23]Essential Oil
Extraction Methods
The primary method for extracting citronella oil is steam distillation, which involves chopping the fresh or partially dried leaves and stems of Cymbopogon nardus or Cymbopogon winterianus into small pieces, loading them into a distillation still on a perforated grid, passing steam generated externally through the plant material to volatilize the oil, and then condensing the vapors in a cooled separator where the oil layer naturally floats and is collected.[24] This process typically operates at temperatures below 100°C to prevent thermal degradation of the oil components and yields approximately 0.5-1.5% oil by weight of the fresh plant material, with average values around 1% under optimal conditions.[19][25] Variations include water distillation (also known as hydro-distillation), where the plant material is submerged in boiling water, which is simpler and suitable for small-scale rural operations but results in lower yields (around 0.5-0.8%) and reduced oil quality due to potential hydrolysis of sensitive compounds.[24][26] Steam distillation generally provides higher efficiency and purer oil compared to water methods, though advanced variants like ohmic-heated hydro-distillation can achieve up to 7.64 mL oil per kWh of energy input, outperforming traditional steam at 1.69 mL/kWh.[26] Solvent extraction, such as using supercritical carbon dioxide, is employed for niche high-purity applications but is less common due to higher costs and complexity, yielding oils with minimal thermal alteration.[27] Following extraction, the crude oil undergoes post-processing steps including separation from hydrosol in the condenser, drying with anhydrous agents like sodium sulfate to remove residual moisture, filtration to eliminate plant debris, and optional rectification through fractional distillation to purify the oil by removing impurities and concentrating key components.[24] In producing regions such as Indonesia and India, field distillation units are commonly used, enabling on-site processing to minimize oil loss during transport.[28] Several factors influence the yield of citronella oil, including plant age, with peak production occurring during the second and third years of plantation when leaf yields reach 20-25 tonnes per hectare, declining thereafter.[19] Harvest timing is critical, with optimal intervals of 2.5-3 months after the initial 6-month establishment, and post-monsoon harvests often yielding higher oil content due to favorable growth conditions; chopping the material prior to distillation can further increase yields by up to 15% by enhancing steam penetration.[25] Regional variations also play a role, as the Java type (C. winterianus) typically produces higher oil yields of 80-100 kg per hectare annually compared to the Ceylon type (C. nardus) at 60-80 kg per hectare.[29]Chemical Composition
Citronella essential oil is predominantly composed of monoterpenoids, including aldehydes, alcohols, and hydrocarbons, which account for over 80% of its content. The primary constituents are citronellal, geraniol, citronellol, and limonene, with relative abundances varying by chemotype. Minor compounds include geranyl acetate, methyl isoeugenol, and trace sesquiterpenes such as elemol and β-cubebene. These components contribute to the oil's characteristic lemony, fresh aroma and its applications in perfumery and repellents.[30] The Ceylon type, derived from Cymbopogon nardus, features lower levels of citronellal (typically 3-15%) compared to the Java type, alongside higher proportions of geraniol (15-25%) and citronellol (5-15%). Limonene is present at 5-10%, while minor compounds like methyl isoeugenol (7-11%) and geranyl acetate (2-5%) are distinctive. In contrast, the Java type from Cymbopogon winterianus exhibits elevated citronellal (32-45%), geraniol (18-24%), and citronellol (11-15%), with geranyl acetate (3-8%) and trace sesquiterpenes (2-5%, e.g., elemol) more prominent. These differences arise from genetic distinctions between the species, influencing the oil's overall profile and quality.[31][30][32]| Compound | Ceylon Type (C. nardus) (%) | Java Type (C. winterianus) (%) |
|---|---|---|
| Citronellal | 3-15 | 32-45 |
| Geraniol | 15-25 | 18-24 |
| Citronellol | 5-15 | 11-15 |
| Limonene | 5-10 | 1-4 |
| Geranyl acetate | 2-5 | 3-8 |
| Methyl isoeugenol | 7-11 | Trace |
| Sesquiterpenes (e.g., elemol) | Trace | 2-5 |