The term “mosquito plant” is a common marketing name for a specific type of scented geranium, often sold with the promise of keeping pests away. Determining whether this plant will return year after year or require replanting is dependent on climate factors. This article clarifies the identity of the plant sold as the “mosquito plant” and explains the factors that make it a perennial or an annual in different regions.
Identifying the Plant Behind the Name
The plant commonly sold as the “mosquito plant” is typically a hybrid geranium, most often marketed under the name Citrosa Geranium or sometimes Pelargonium citrosum. Although the scientific name Pelargonium citrosum is frequently used, it is not a valid taxonomic designation; the plant is actually a cultivar within the Pelargonium genus. The plant is botanically distinct from true Citronella Grass (Cymbopogon nardus), which is the source of commercial citronella oil. The hybrid geranium emits a powerful, pleasant citronella-like or lemony scent when its leaves are crushed or brushed against. The plant has lacy, medium-green foliage and produces clusters of delicate pink to lavender flowers during the growing season.
Hardiness Zones: The Perennial vs. Annual Determination
The question of whether the mosquito plant is a perennial or an annual depends entirely on the local climate and the plant’s ability to survive winter temperatures. The plant is technically a tender perennial subshrub, meaning it can live for multiple years under the right conditions. Specifically, this Pelargonium hybrid is hardy only in United States Department of Agriculture (USDA) Hardiness Zones 9 through 11. In these warm zones, which include parts of the southernmost US, the plant can be left outdoors year-round and will grow, sometimes reaching up to six feet tall.
In the majority of the US, which falls into colder zones (Zone 8 and below), the mosquito plant cannot survive the winter frost. When grown in these regions, it must be treated as an annual. Gardeners who wish to keep the plant for more than one season must bring it indoors before the first hard frost arrives.
Overwintering the plant involves pruning the stems back and placing the potted plant in a cool, bright location indoors for the winter months. The indoor environment should maintain temperatures between 50 and 60 degrees Fahrenheit to allow the plant to rest without going completely dormant. Watering should be significantly reduced during this time to prevent root rot, as the plant is not actively growing. Once spring arrives and the danger of frost has passed, the mosquito plant can be gradually reintroduced to the outdoors.
How Effective is the Plant at Repelling Mosquitoes?
The primary appeal of the mosquito plant is its supposed ability to repel insects, a claim that is often not supported by scientific evidence for the living plant itself. The plant contains essential oil compounds, such as geraniol and citronellol, which are known to have repellent properties when extracted and concentrated. However, the living plant does not continuously release enough of these volatile compounds into the air to create an effective protective barrier.
Scientific field evaluations have shown that people sitting near an intact mosquito plant received the same number of bites as those who were untreated with repellent. Researchers noted that mosquitoes were regularly observed landing and resting directly on the plant’s foliage, indicating a lack of repellency. The plant’s oil is only released in significant amounts when the leaves are physically disturbed, such as by crushing or rubbing them.
For the plant to offer any protection, a person would need to physically rub the foliage onto their skin to transfer the essential oils, which is the same principle as applying a topical repellent. Therefore, while the plant offers a pleasant, citrusy fragrance, it should not be relied upon as a primary method for mosquito control.