The citronella plant is a popular garden addition, primarily sought after for its distinct citrus scent and supposed ability to deter pests. This fragrance comes from volatile oils in the leaves, released when the foliage is brushed or crushed. Despite its tropical origin, the plant is highly sensitive to cold. Exposure to low temperatures quickly leads to irreversible damage.
Distinguishing the Citronella Plant Types
The term “citronella plant” often causes confusion because it applies to two botanically distinct species with vastly different cold tolerances. The plant most commonly sold in garden centers is a scented geranium, Pelargonium citrosum, sometimes called the ‘Mosquito Plant.’ This variety is a tender perennial reliably hardy only in the mildest climates (USDA Hardiness Zones 9 through 11).
The true source of commercial citronella oil is Citronella Grass (Cymbopogon nardus or C. winterianus). This grass is significantly hardier than the geranium but is less common in residential sales. Gardeners should recognize the broad-leafed scented geranium (Pelargonium) as a tropical plant that must be treated as an annual in most regions.
Minimum Survival Temperatures
The commonly grown Pelargonium citrosum is extremely intolerant of cold. Nighttime temperatures consistently below 50°F (10°C) cause the plant to slow growth and struggle. The threshold for action is 45°F (7°C), as consistent exposure at or below this point causes significant stress.
The critical danger zone begins just above freezing; the plant is frost-tender and will not survive a freeze. Exposure to 32°F (0°C), even briefly, is typically lethal because the water inside the plant’s cells freezes, rupturing the cell walls. This damage is irreversible and leads quickly to the plant’s death.
Visible signs of cold damage appear quickly after exposure to temperatures below 40°F. The foliage develops a water-soaked appearance, followed by wilting and discoloration, often turning black or brown and becoming mushy. Stems may also blacken near the base, indicating the collapse of vascular tissue.
Strategies for Cold Weather Survival
Since the citronella plant lacks natural cold-hardiness, gardeners in cooler climates must take proactive measures to ensure its survival. The most effective strategy for managing short-term cold snaps is to provide immediate, temporary shelter. For container plants, move them onto a covered porch, into a garage, or against a warm, south-facing wall to shield them from wind and heat loss.
Bringing Plants Indoors
For long-term protection, the plant must be brought indoors before the 45°F temperature threshold is reached. Before moving inside, inspect the plant for pests and prune it back by about one-third of its growth. This pruning helps manage the plant’s size for indoor placement and encourages bushier growth in the spring.
Once indoors, the plant requires a location that receives ample bright light, such as a south or west-facing window or supplemental light. Watering frequency should be significantly reduced during the winter, allowing the top inch or two of soil to dry completely between waterings. This reduction prevents root rot, which is common when the plant’s growth slows.
Propagating Cuttings
As an alternative to overwintering the entire plant, gardeners can take stem cuttings in the late summer or fall. Root these cuttings in water or soil to ensure a fresh, young plant for the following season.