THE SHORT ANSWER
Sitting in a pot, almost nothing. The repellent compounds in citronella, lavender and scented geraniums are locked in the leaf and only released when it is crushed. A meta-analysis of 62 studies found none had even examined landscape plantings — the premise has essentially never been tested because it does not hold.
GROWING IN A POT
No measurable effect
LEAVES CRUSHED ON SKIN
Works, briefly
THE MOSQUITO PLANT
Debunked repeatedly
WHAT DOES WORK
Habitat, fans, repellent
Do mosquito-repellent plants work?
Clemson Extension’s summary of the evidence is the clearest statement of the problem. A meta-analysis published in the Malaria Journal reviewed 62 studies on plant essential oils and their ability to repel Anopheles mosquitoes. Fifty-six were laboratory work. Six were field studies. None of them examined landscape plantings.
That is the whole issue in one line. There is a real body of research showing that these compounds repel mosquitoes — when they are extracted, concentrated, and applied. There is almost nothing showing that a living plant in the ground does anything at all, because the fragrance it releases dissipates into the air and any breeze removes what little there was.
Mississippi State Extension reaches the same place from the practical end: a few scattered plants are unlikely to make any real difference to the mosquito population around a house.
A 2026 field trial in the Journal of Medical Entomology tested exactly this — citronella-scented geranium and prostrate rosemary, evaluated for spatial repellency against host-seeking mosquitoes. Neither plant reduced catch rates compared with controls.
The plant sold as the “mosquito plant” is the worst of them
Every garden centre carries it from May: lacy foliage, pink-purple flowers, a label that says Mosquito Plant. It is Pelargonium citrosum, the citrosa geranium, and it is marketed almost exclusively on this one claim.
The Herb Society of America’s guide to pelargoniums reports that its oil composition is very close to rose geranium, containing only about 0.09% citronellal — one of the active components of citronella oil. In testing, the citrosa plant did not protect human subjects from mosquito bites any better than the controls. In one field trial, mosquitoes landed on the plant.
Research from the University of Guelph found no repellent properties, and Colorado State has noted that despite the name it does not contain citronella oil. It is a pleasant scented geranium sold on a property it does not have.
If you want a scented geranium with genuine repellent compounds in it, buy Pelargonium graveolens — the rose-scented one — which contains geraniol and citronellol. You will still have to crush it.
Why they only work crushed
The repellent chemistry — citronellal, citronellol, geraniol, nepetalactone — sits inside oil glands in the leaf tissue. An intact growing leaf holds onto it. That is the point of the oil from the plant’s perspective: it is a defence released when something damages the leaf, not a cloud the plant maintains around itself.
Break the leaf and you release it. Rub it on skin and you have a genuine, if brief, repellent. Both Clemson and Mississippi State make the same recommendation: crushed plant material rubbed on skin or clothing does more than the plant’s presence ever will.
Two caveats on that. The protection is short — measured in tens of minutes rather than hours, so it needs reapplying constantly. And Mississippi State warns that the volatile oils themselves can irritate skin, so test a small patch before you rub handfuls of anything on a child.
The plants that at least contain something
If you are going to plant for this, plant the ones carrying real concentrations of the active compounds, and treat them as an ingredient rather than a barrier.
A note on pets. Pelargoniums — including the scented geraniums above — are listed by the ASPCA as toxic to dogs and cats. If you have an animal that chews things, that is worth knowing before you plant a row of them at nose height.
The one exception worth mentioning
In the interest of not simply debunking: there is a reported field study from Tanzania in which lantana planted around houses was associated with a substantial reduction in indoor mosquito density, including a large drop in one primary malaria vector. It is one of the very few results suggesting live, unprocessed plants can reduce mosquito numbers.
Treat it as interesting rather than transferable. That was dense planting around traditional open-eaved housing, targeting particular Anopheles species, in a very different climate. It is not evidence that three pots of lantana on an American deck will change your evening. It is evidence that the question is not entirely closed.
What actually reduces mosquitoes in a yard
If the goal is fewer mosquitoes rather than a nice-smelling border, the order of effectiveness is unglamorous and well established.
Remove standing water. Mosquito larvae are aquatic and a generation needs roughly a week and about a bottle cap of water. The gutter run holding water because it has dropped out of pitch, the sagging tarp, the plant saucers, the bird bath nobody empties, the corrugated downspout extension — that is where they are coming from, and it is almost always closer than people expect.
Put a fan on the patio. Mosquitoes are poor fliers in moving air, and an oscillating fan clears a seating area more reliably than anything you can plant.
Use a registered repellent on skin. DEET or picaridin, applied properly. This is the part the plants are trying to substitute for and cannot.
Plant the herbs because they are useful and smell good. Just do not buy them expecting a force field.
WHERE THIS STOPS BEING A GARDENING PROBLEM
You have cleared every container and the numbers have not moved. That means the breeding site is somewhere you have not looked or cannot reach — a neglected pool, a blocked drain, a ditch, a neighbouring lot that holds water for a week after rain.
The biting is happening at dusk and you cannot see what is doing it. That may not be mosquitoes at all. No-see-ums breed in damp soil rather than standing water, which is why clearing water changes nothing for them.
Standing water you cannot legally or physically drain. A wetland margin, a retention pond, a drainage easement. That is habitat work and permission, not a hose and an afternoon.
Cleared the standing water and still swarmed at dusk? Call (877) 360-4657
Common questions
Does the citronella plant repel mosquitoes?
Not while it is growing. The oil has to be released from the leaf and applied. The plant marketed as the “mosquito plant” contains only about 0.09% citronellal and failed to protect test subjects better than controls.
What plants keep mosquitoes away?
None, by simply being planted. Lemon balm, citronella grass, rose-scented geranium, catnip and lemon thyme contain genuine repellent compounds, but the leaves must be crushed and applied to skin for any effect.
Do marigolds repel mosquitoes?
There is no good evidence that planted marigolds reduce mosquito numbers. They are frequently listed, and the listing traces back to laboratory work on extracted compounds rather than to any study of garden plantings.
How long does crushed leaf repellent last?
Tens of minutes, not hours — the volatile oils evaporate quickly. It also needs reapplying after sweating. Test on a small patch of skin first, since the oils themselves can irritate.
Are mosquito plants safe for dogs?
Pelargoniums, including scented geraniums and the “mosquito plant”, are listed by the ASPCA as toxic to dogs and cats. Worth checking before planting them where an animal browses.
What is the most effective way to reduce mosquitoes?
Eliminate standing water, since larvae need it and a generation takes about a week. Then a fan on the patio and a registered repellent on skin. Habitat first, chemistry second, plants a distant third.
Sources. The Malaria Journal meta-analysis and the crushed-leaf requirement follow Clemson Cooperative Extension. Practical limits of scattered plantings and the skin-irritation caution follow Mississippi State University Extension. Citrosa oil composition and field-trial results are reported in the Herb Society of America’s pelargoniums guide; further negative findings are attributed to the University of Guelph and Colorado State University. The 2026 spatial repellency trial appeared in the Journal of Medical Entomology. The lantana result is reported from a field study in Tanzania and is described here as a single exception rather than transferable guidance.
Related
- How to get rid of mosquitoes — the habitat work that actually moves the numbers
- No-see-ums — if you are being bitten by something you cannot see
- Professional mosquito control — when the breeding site is off your property
