Citronella is a term you might associate with candles or sprays. Gardeners know that burning citronella candles during an outdoor activity provides some protection against pesky insect intrusions and bites. Yet did you know that when it comes down to finding the source of the citronella oil there are actually three contenders? In addition, two kinds of ants lay claim to citronella in their names.
You may know the citronella plant (pelargonium citrosum) also as the mosquito plant. In spite of its name, it is not the plant that yields citronella oil. The citronella plant is a member of the geraniaceae family. As an annual plant, it grows to a height of about 24 to 36 inches. The plant prefers sun or partial shade and grows well in USDA planting zones 9b, 10a, 10b and 11. You may enjoy its strong fragrance and find that it is a welcome addition to your xeriscape.
The Chilean citronella tree (citronella mucronata) is a member of the cardiopteridaceae family, although some horticulturists argue that it belongs with the icacinaceae. Native to Chile, you may also know the tree under the name huillipatagua. It grows to a height of about 33 feet. Hobbyists in humid climates may use the citronella tree as an ornamental species. The tree does well in USDA planting zone 8. In spite of its name, it does not yield the aromatic citronella oil.
The third contender for the source of citronella oil and the term "citronella" in its name is citronella grass (cymbopogon nardus). It is part of the poaceae family. It is a native plant of Puerto Rico and the U.S. Virgin Islands that has been introduced into other areas as well. The grass can grow to an average height of about 5 feet. Plant it in full sun or partial shade in USDA planting zones 10a, 10b and 11. If you have acidic or extremely alkaline soil, this plant will nevertheless grow well.
As a gardening hobbyist, you are probably familiar with citronella candles. The essential citronella oil required to make them can come from citronella grass. As an insect repellent, the Environmental Protection Agency shows it to be effective against mosquitoes, fleas, ticks and also black flies. Citronella does not harm the insects but the odor makes it difficult for the pests to lock in on a host. Be careful if using citronella-containing products that you need rub onto your skin; in some cases the substance may cause irritation.
Another type of life form that has the term "citronella" in its name is the citronella ant (acanthomyops interjectus or acanthomyops claviger). They have no relationship to citronella plants. Rather, the name refers to the strong citronella scent the insects release in the presence of predators. They exist throughout the United States but are most common in the eastern portion of the country, where their yellowish color gets them mistaken for termites. Unlike termites, citronella ants do not harm a dwelling's wood structures but depend on the sugary secretions of aphids for sustenance.