Citronella grass, Cymbopogon nardus, is a tropical clumping grass best known for its intense citrus-like scent. It is a close relative of culinary lemon grass with similar long, narrow leaves and cane-like stems. Other common names include blue citronella grass, nard grass, and mana grass. Citronella grass originated in southeast Asia but is now grown deliberately, or has naturalized, throughout much of the tropics. It is commercially grown in many areas for extraction of its aromatic oil, and is also planted as a garden or landscape ornamental in warm climates.
The recommended setting for citronella grass is in full sun on well-drained soil of at least average fertility. It is a perennial from U.S. Department of Agriculture (USDA) planting zone 10 south through the tropics. Citronella grass can also be grown as an annual grass where the growing season is both warm enough and long enough. As it grows, the grass forms a clump often as wide as it is tall, and can reach from 5 to 6 feet (1.5 to 1.8 m) in optimal growing conditions. Citronella grass typically requires at least 30 inches (76 cm) of water per year to thrive.
This plant is usually best placed where the intense fragrance of the leaves can be enjoyed. Citronella oil, in high enough concentration, is thought to be a natural insect repellent, and the grass is sometimes described as mosquito repelling grass. Most experts agree, however, that the concentration of the scent near the live grass is not enough to affect insects.
The grass is grown commercially as a source of aromatic oil in many tropical areas including India, Indonesia and central America. It was originally used as mosquito repellent, and some insect repellent citronella products are still made. Much of the insect repellent market, however, has been lost to more effective synthetic products. Current use of the oil is mostly as a scenting agent for inexpensive cleaning products, including detergents and sprays.
Citronella grass has naturalized in many places that have suitable year-round temperatures and sufficient rainfall to sustain growth. It spreads most easily in grasslands and open woodland. In parts of tropical Africa it is considered a weed on pasture land and requires a significant effort to control it. Control is complicated by the practice of burning fields for weed suppression. Studies show that citronella grass easily recovers from annual burning and readily spreads by seed into areas previously covered by other plants.