The plant commonly known as “citronella” is popular for outdoor spaces, largely due to its perceived ability to repel mosquitoes. Whether this plant lives for one season or many hinges on two basic botanical terms: an annual completes its life cycle within a single growing season and dies, while a perennial regrows year after year. For the citronella plant, its status depends almost entirely on local environmental conditions and the specific care it receives.
The Two Plants Labeled Citronella
Confusion about the plant’s lifespan often begins with its identity, as two distinct species are frequently sold under the same common name. The plant most often purchased as a potted “citronella plant” is the scented geranium, Pelargonium citrosum ‘Citrosum’. This plant has deeply lobed leaves that emit a distinct lemon-like aroma when bruised or crushed.
The second plant is Citronella Grass (Cymbopogon nardus or Cymbopogon winterianus), which is the commercial source of citronella oil used in candles and sprays. While both plants are aromatic, this discussion focuses primarily on the Pelargonium species, which is typically treated as a temporary patio plant and often considered an annual.
Natural Climate Requirements for Perennial Growth
For the Pelargonium citrosum to survive outdoors year-round as a true perennial, it must be protected from freezing temperatures. The USDA Plant Hardiness Zone Map provides the geographic context to determine this longevity. The perennial threshold for this species is typically found within USDA Zones 9 through 11, where the average minimum winter temperature remains relatively high.
In these mild regions, such as parts of the Gulf Coast and the Pacific Southwest, the plant rarely encounters sustained cold weather and can continue its growth cycle indefinitely. The scented geranium is extremely sensitive to frost. Even a light frost causes significant damage, and a hard freeze is almost always lethal.
Temperatures must remain consistently above freezing, generally above 40 degrees Fahrenheit (4.5 degrees Celsius), for the plant to survive outdoors. This sensitivity dictates that in Zone 8 and lower-numbered zones, the plant is functionally an annual. In these colder areas, the growing season ends with the first autumn frost, forcing gardeners to replace the plant the following spring.
Techniques for Indoor Overwintering
Gardeners living outside Zones 9-11 can extend the life of their scented geranium through managed overwintering. The most straightforward method involves bringing the entire potted plant indoors before the first predicted frost. Before the move, prune the plant back by one-third to one-half of its size. This reduces stress and limits the risk of bringing in outdoor pests.
Once inside, the plant requires a location that is bright and cool, ideally with temperatures between 50 and 65 degrees Fahrenheit (10 to 18 degrees Celsius). Placing the pot near a sunny window or under supplemental grow lights ensures it receives necessary light. Keep the plants away from heat vents or fireplaces, as they prefer cooler conditions.
Watering must be drastically reduced during this period, allowing the soil to dry out almost completely between applications, since the plant’s growth slows considerably. Overwatering during this semi-dormant phase can quickly lead to root rot or fungal issues. If the plant begins to look spindly or “leggy” due to reduced light, pinch the stems back just above a leaf node to encourage bushier growth.
An alternative strategy is to propagate the plant by taking stem cuttings in the late summer or early fall. Cuttings should be taken from non-flowering shoots and rooted in a moist potting medium. This offers a space-saving way to preserve the plant’s genetics, allowing the cultivation of smaller, more manageable plants indoors over the winter. These can then be transplanted back outdoors once the danger of freezing temperatures has passed.