The question of whether a “mosquito plant” is a perennial depends heavily on your climate and the plant’s botanical classification. This plant, often sold as Citrosa Geranium (Pelargonium citrosum), is marketed for its citrusy scent, which resembles that of true Citronella grass. Understanding its correct botanical classification and its natural hardiness is key to determining its lifespan in your garden. The distinction between its life cycle and its ability to survive a cold winter is the core issue for most gardeners.
Identifying the Ambiguous “Mosquito Plant”
The plant most commonly labeled a “mosquito plant” or “Citronella Geranium” is Pelargonium citrosum, sometimes referred to as Pelargonium citriodorum or a cultivar of Pelargonium graveolens. This scented geranium is frequently confused with Citronella Grass (Cymbopogon nardus), the source of commercial citronella oil. Both plants produce a lemony aroma, but they belong to entirely different botanical families and have distinct growth habits. The geranium’s fragrance comes from the citronellol and geraniol compounds stored within the leaves, which are released when the foliage is crushed. The plant’s reputation for repelling insects is often an association with the highly concentrated oil derived from the true Citronella grass.
Horticultural Classification: Perennial or Tender?
The Pelargonium “mosquito plant” is technically a perennial subshrub, but only in consistently warm environments. A true perennial is a plant that lives for more than two years and typically survives harsh winter conditions outdoors. The mosquito plant, however, is considered a “tender perennial” in most temperate climates, meaning it cannot tolerate frost or freezing temperatures. It will only survive year-round outdoors in USDA hardiness zones 9 through 11, where temperatures rarely fall below freezing. In any region colder than Zone 9, the plant is effectively an annual, meaning it will die off completely when the first hard frost arrives. Gardeners in these colder zones must treat it as a seasonal plant unless they intervene to keep it alive through the winter months.
Techniques for Overwintering and Year-Round Survival
For gardeners in colder regions, keeping the mosquito plant alive across the winter requires treating it as a temporary houseplant or propagating new stock. The simplest method is to bring the entire potted plant indoors before nighttime temperatures consistently drop below 45°F. Once inside, the plant’s growth naturally slows down, requiring a period of semi-dormancy with significantly reduced care.
Overwintering the Potted Plant
Place the pot in a sunny, south-facing window, ensuring it receives at least six hours of bright light daily. This prevents the plant from becoming “leggy” or stretched out. Water the plant sparingly, only when the top inch of soil is completely dry to the touch, as overwatering is the most common cause of indoor death during winter.
Propagating Cuttings
A second, space-saving option is to take stem cuttings in the late summer or early fall. Snip healthy, four-to-six-inch non-flowering shoots, strip off the lower leaves, and root them in moist potting mix or a glass of water. These small, new plants can be kept in a bright location all winter and will be ready for planting outdoors after the last spring frost.
Scientific Efficacy of Mosquito Repellency
The mosquito plant’s effectiveness as a stationary mosquito repellent is limited. Scientific studies have shown that the intact plant offers minimal protection against biting insects. The repelling chemicals, like citronellol, are only released in significant concentration when the plant’s leaves are physically crushed. This crushing is not a constant occurrence in a garden or patio setting. The concentrated essential oil derived from true Citronella Grass is a recognized repellent ingredient, but the live geranium plant itself is primarily an ornamental herb that must be paired with other methods for effective mosquito control.