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Citronella Plant Pointers: Fragrant Friends

Citronella oil, the savior in the battle against the mighty mosquito! If you live in a warm humid climate then you will have heard of citronella as the oil used in a burner, a candle or a cosmetic lotion smothered on the skin to repel mosquitoes from biting. But, do you know where it comes from? Well, let me introduce you to the citronella plant, Cymbopogon nardus!

The citronella plant is not to be confused with another lemony ‘supposed’’ insect repellent plant, the scented geranium, Pelargonium citrosum.  The scented geranium, sometimes called citronella geranium, is easy on the eye and smells amazing, but it does nothing in the battle against pests.

The true citronella plant is a large tufted perennial grass growing to 6ft tall (1.8m) and 4ft wide (1.2m) in the right conditions.  It’s the oil contained within the leaves that repels insects and it can only be harvested through crushing the leaves.  The existence of these grasses alone will not deter mosquitos. 

Citronella oil has a long history of medicinal use such as treating lice, parasites, or worms, as well as relieving migraines and fevers.  Its antibacterial, antimicrobial, anti-inflammatory, and anti-fungal properties make it useful in both cleaning and cosmetic products providing them with an unmistakable lemon scent.

Quick Care Guide

Citronella plant
The citronella plant is a grassy, lemon-scented species. Source: Ahmad Fuad Morad
Common Namecitronella plant, mosquito plant, citronella grass, geranium grass, and nardus grass
Scientific NameCymbopogon nardus, Cymbopogon winterianus
FamilyPoaceae
Height & Spread6ft x 4ft
LightFull sun to partial shade
SoilLoam
WaterConsistent regular watering
Pests & DiseasesLeaf blight

All About The Citronella Plant

Top of citronella flower stalk
The top of a citronella grass flower stalk. Source: Dr. Alexey Yakovlev

If you find a plant at garden centers with the botanical name Cymbopogon nardus or Cymbopogon winterianus then you can be confident you have discovered the commonly known citronella plant, also known as citronella grass, geranium grass, mosquito plant, and nardus grass. It comes from the plant family Poaceae. The citronella grass plant is an upright tufted grass with lance-shaped bluish-green leaves sprouting from long brownish-red erect stems and growing to 3-4 ft long (90-120cm).

Citronella grass is an aromatic evergreen perennial, native to Sri Lanka but common in most warm-temperate, subtropical and tropical regions of Asia and Africa.  In cooler climates, citronella is grown as an annual and brought indoors over winter. It’s closely related to lemon grass.

When optimum conditions are met for growing, the citronella grass plant will produce panicles of flowers on spikelets borne on long flowering stems protruding up to 6ft from the center of the plant.  These flowers will readily self-seed but require consistent temperatures of between 20-22 C to germinate. Seeds are light brown, dry, and typical of grasses/cereals.  Plants grown in cooler climates are less likely to produce viable flowers. 

Plants will spread naturally through creeping underground rhizomes and can become somewhat invasive in their natural tropical climate with its vigorous growing habit, out-competing existing flora and cultivated crops.

Citronella grass is typically grown for its insect repellent properties.  Many gardeners believe that the citrus aroma of plants is enough to repel mosquitos but unfortunately this is not true.  It is the citronella oil contained within the leaves that is used in mosquito repellents, but it must be extracted first through the process of distillation.  If you simply crush the leaves by hand you will release some oil, but not enough for repelling mosquitoes. Nonetheless, some gardeners swear that crushing and rubbing the leaves on their skin is one of the natural ways to apply a mosquito repellent, and that scent may be successful in keeping a few mosquitoes away while you’re working in the garden!

The extracted essential oil has a strong fragrance of lemon often used to perfume cosmetics, soaps, deodorants, and skin lotions specifically used as mosquito repellents.  Citronella candles and oil burners are used at night as mosquito repellent.  The anti-bacterial and anti-fungal nature of the oil makes it perfect for cleaning and disinfecting products.  Caution should be used when using these products.  Inhaling the oil vapors can cause an allergic reaction in some people and citronella oil may also irritate sensitive skin. The citronella plant is not edible, unlike its close cousin Cymbopogon citratus, commonly known as lemon grass.

If you have bought a ‘citronella plant’ with lacy foliage and a citrus scent, then it is most likely you have lemon-scented geranium, sometimes called the citronella geranium.  They smell similar to citronella grass, but the leaves do not contain the insect repellent citronella oil and therefore are ineffective at keeping those pesky mosquitoes from biting. Unfortunately, members of the geranium family may be beautiful plants for your garden amongst other flowers, but they just don’t repel mosquitoes well!

Planting Citronella Plant

Citronella can be planted throughout the year if grown in tropical, subtropical, or warm temperate climates.  As a vigorous grower, mosquito plants won’t take long to establish. In cooler climates wait until late spring to early summer before planting out into the garden.   

Choose a location in full sun with some partial shade at the hottest part of the day.  Leaves can become easily scorched and look unsightly. Citronella grass is adaptable to most soil types, but the mosquito plant prefers moist loam-based soil that is well-draining.

Growing mosquito plants from seed is not recommended as germination can be erratic.  The vigorous growth and rhizomatic roots make it a prime candidate for propagation from division. 

Citronella grass is perfect for growing as container plants as it allows you to move plants into a variety of locations to suit your needs.  You may need to invest in larger pots as your container plants outgrow smaller containers, or simply divide the plant and replant a division in the same container and share the others with fellow gardeners.  Container growing is a good option for colder zones as it allows your plant to be easily moved indoors over winter to protect them from frost. 

Care

Base of citronella plant
The base of the citronella plant. Source: Ahmad Fuad Morad

Citronella grass is native to the tropics. However, it is very adaptable to cooler climates if you know how to look after it. Let’s talk about the plant, information you’ll need to know to care for it, and maintaining its lovely foliage in your garden!

Sun and Temperature

Citronella is primarily a sub-tropical grass with a preference for full sun (at least six hours) and warm temperatures.  In very hot climates provide shade or filtered sunlight during the hottest time of the day to prevent the leaves from scorching, make certain it gets at least six hours of sunlight. 

Don’t let this plant’s tropical origins put you off growing it if you are located north of the equator!  Hardy to USDA zones 10-12, the citronella plant can tolerate temperatures down to 32ºF (0ºC) but will not tolerate prolonged periods of frost. Bring your citronella grass indoors in large pots when the first frost is forecast.

Water and Humidity

Provide long deep drinks when the soil begins to dry out or provide irrigation through soaker/drip hoses to maintain consistent moisture.  Citronella grass prefers consistently moist soil but surprisingly can tolerate long periods of drought. Reduce watering during the winter months but check regularly to ensure plants have not completely dried out, especially those grown in containers. A soaker hose or other form of drip irrigation at the base of the plant can be used to aid in watering your garden.

Soil

For optimum results grow citronella in a rich loam-based, free-draining soil or compost. Citronella grass is very adaptive to most soil types and once established will do well.  Where soils are very poor, dig in some organic matter before planting to provide nutrients and to help with moisture retention.  Soil pH should be neutral.

Fertilizing

Fertilize citronella grass once a year in spring with a good quality slow-release nitrogen-rich fertilizer. If your plant is looking a little lackluster, then a quick feed with a liquid nitrogen fertilizer should bring it back to healthy growing habits. Adding a top inch of compost once or twice a year around the base of your plant will also work in lieu of fertilizers.

Pruning

Citronella plants require little or no pruning when grown in their natural environment. At most, perhaps they can benefit from the odd trim of brown leaves and deadheading to prevent self-seeding. Plants grown in containers in cooler climates will benefit from a hard prune to 6 inches (15cm) above the crown before bringing them into a sheltered area or indoors over winter. New shoots will appear in spring ready for going back outside.

Propagation

Citronella grass is unlikely to develop viable seeds unless grown in optimum climate conditions.  Even with viable seeds, germination is erratic. The main form of propagation for citronella plants is via division. The vigorous growing nature of citronella grass lends itself perfectly for division to keep plant size under control.  It’s also a great way to keep container-grown plants in check.

Divide plants that are at least 2-3 years old and have developed a good root system.  Dig up the entire plant and using a saw, spade or knife divide the plant into as many divisions you require.  Pot each division up individually or replant into new positions in the garden.  Water well until plants are established. If using this method, make sure there’s ample time for the new mosquito plants to become well-established before the first frost.

Root cuttings are another option if you don’t wish to dig up an entire plant. Root cuttings should be taken in winter when plants are dormant and their roots are nutrient-rich, thus giving cuttings the best chance to develop.  Simply remove soil from the base of the plant until roots are visible and cut off 2-3 inches of root with a clean pair of snips. Place the cutting into a pot of compost and place somewhere bright and warm, keeping the compost moist.  Shoots should appear in early spring.

Troubleshooting

Citronella geranium
Citronella geranium is not the same as the citronella plant. Source: Starr

Citronella is an easy plant to look after with few growing problems.  Here are a couple of things to look out for just in case.

Growing Problems

Your mosquito plant benefits from afternoon shade to protect the leaves from sun scorch during the hottest time of the day.  The scorched leaves are unsightly and the damage reduces the plant’s ability to photosynthesize thus reducing the plant’s overall health.

Wet feet can also be a problem for citronella plants.  Although they prefer soil to be consistently moist, heavy wet soil will reduce the ability of the plant to take up nutrients from the soil and will cause plants to deteriorate. It may even cause root rot and the death of the plant.  Grow citronella grass in free-draining, loam-based soil to avoid this growing problem.

Pests

Citronella grass tends not to be affected by pests.

Diseases

Commercially grown citronella grass can be subject to leaf blight.  This is particularly prevalent in sub-tropical climates where plants are grown densely to produce citronella oil. Lack of air circulation provides perfect conditions for blight to take hold and will result in a reduction in both the quantity and quality of oil extracted.  Blight is less common in domestic gardens unless plants are allowed to become very congested.  Signs of blight are dark spots or lesions on leaves from which necrosis begins to rot the leaves.  Remove and destroy affected leaves immediately.  Divide congested plants every few years and remove dead or dying foliage to improve air circulation. Copper fungicides may be useful to help prevent blight.

Frequently Asked Questions

Mission grass and citronella grass
Mission grass in the forefront, with citronella grass flowers to the back right. Source: Dinesh Valke

Q: Do citronella plants really keep mosquitoes away?

A: The oil extracted from the leaves of citronella plants has some mosquito repellent qualities when used in candles, lotions, and oil burners.  The plants in their natural form do not help in repelling mosquitoes.

Q: Does citronella plant like sun or shade?

A: Citronella plant likes to grow in a bright sunny spot, but will benefit from some shade at the hottest part of the day to protect leaves from scorch.

Q: Is citronella a good houseplant?

A: Citronella is often confused with the citronella geranium or scented geraniums (pelargonium citrosum), which have a lemony scent and make excellent houseplants. Unfortunately, the citronella geranium does not repel mosquitoes.  True citronella plants are large grasses growing up to 6ft tall and 4ft wide and are unsuitable for most indoor growth for very long. It does make for an excellent patio plant as most people have enough room on their patio for a larger species.


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