Pelargonium citrosum (Citronella Geranium)
Pelargonium citrosum (Citronella Geranium)
Contents
Introduction & History
Citronella Geranium is the popular 'mosquito plant' sold in garden centres with claims of repelling insects by merely growing on your patio. While the citronella-like scent is genuine and pleasant, the repellent claims are significantly overstated — the plant must be crushed and rubbed to release enough oil for any meaningful effect. Nevertheless, it's a lovely aromatic foliage plant with deeply cut, lacy leaves and a bright lemon-citronella fragrance.
History & Origin
A cultivar of uncertain parentage — likely a hybrid of Pelargonium graveolens and/or P. citronellum. Marketed heavily in the 1990s as the 'mosquito plant' or 'citrosa plant' based on claims (by the Dutch biotech company that promoted it) that it was genetically engineered with citronella genes. These claims were misleading — it's a naturally scented pelargonium, not a transgenic creation. The marketing was more impressive than the repellent effect.
Botanical Description
Tender, bushy perennial growing 40–80 cm tall. Leaves are large, deeply palmate-lobed with finely cut, almost fern-like divisions — more finely divided than rose geranium. The foliage is grey-green and strongly citronella-scented when touched. Small, pale pink to lavender flowers appear in clusters in summer. The overall habit is more compact and lacy than P. graveolens.
Stem: Semi-woody to woody at base • Height: 60 cm at maturity • Spread: 45 cm • Foliage: green • Flowers: pink-lavender (summer)
Planting & Cultivation
Same as rose geranium — plant after frost, full sun, well-drained soil. Space 40–50 cm apart for summer bedding. Container growing is standard in all but frost-free climates. Position near seating areas where the leaves can be brushed for fragrance release — the living plant alone has negligible mosquito-repelling effect at distance.
| Sun exposure | Full Sun |
| Soil pH | 5.5-6.5 |
| Spacing | 45 cm |
| Seed depth | 3–6 mm (surface-sow if light-dependent germinator) |
| Water needs | Moderate |
| Soil type | Well-drained, humus-rich loam; add perlite or grit for drainage |
Cultivation Details
Same as rose geranium — full sun, well-drained soil, regular pinching for bushiness. Feed monthly. Water moderately. The finely divided leaves are attractive as a foliage plant regardless of any repellent claims. Fast-growing; can become leggy without regular pinching. Take cuttings in late summer for overwintering.
Climate & Hardiness
Tender — same as all pelargoniums. Frost-sensitive below −2°C (zones 10–11 outdoors). Container growing and indoor overwintering in cold climates. Same culture requirements as rose geranium.
USDA zones: 9-11
Minimum temperature: 0°C
Drought tolerance: Yes — established plants tolerate dry spells
Indoor growing: Suitable for windowsill culture with 6+ hours light
Seasonal Care
Same as rose geranium. Spring: plant out after frost. Summer: enjoy the fragrance; pinch for bushiness. Autumn: take cuttings; bring indoors. Winter: bright, cool windowsill.
Propagation
Easy from stem cuttings — 8–10 cm tips root in 2–3 weeks. Same technique as rose geranium. Let cut ends callous for a few hours before inserting in medium. Take cuttings in August–September for next year's plants.
| Method | Success rate | Time | Notes |
|---|---|---|---|
| Stem cuttings | 70–90% | 2—4 weeks | Softwood in spring, semi-ripe in summer; 8–12 cm |
| Division | 95%+ | Immediate | Split established clumps in spring or autumn |
| Seed | 50–80% | 14–28 days | Some require cold stratification; germination variable |
| Layering | 80–90% | 6–12 weeks | Pin low branch to soil; sever when rooted |
Diseases & Pests
Same as rose geranium — whitefly, aphids, botrytis. The irony of the 'mosquito plant' label is that the plant itself doesn't significantly repel the pests around it. Good air circulation and careful watering prevent most problems.
Culinary Uses
Minor culinary use — the citronella-like flavour is less refined than rose geranium for cooking. The leaves can infuse sugar or cream with a lemony note, but lemon balm or lemon verbena are preferable for culinary applications. The flowers are edible as a mild garnish. Not a significant culinary herb.
| Category | Pairing suggestions |
|---|---|
| Baking | Shortbread, scones, cakes |
| Preserves | Jelly, syrup, sugar |
| Cocktails | Gin botanicals, spritzers |
| Honey | Infused honey, dessert garnish |
Medicinal & Aromatherapy
Contains citronellol, geraniol, and other terpenoids. The scent is uplifting and energising. Crushed leaves on skin provide mild, temporary insect deterrence — better than nothing but far less effective than commercial citronella products. Traditional uses include headache relief and as a calming scent. The essential oil is occasionally used in aromatherapy blends.
| Compound | Properties |
|---|---|
| linalool | floral, calming |
| cineole | camphoraceous, expectorant |
| thymol | antiseptic, warm |
| carvacrol | pungent, antimicrobial |
| eugenol | clove-like, analgesic |
Container & Companion Growing
Container Growing
Standard growing method — same as rose geranium. The lacy, finely divided foliage makes it an attractive container specimen. Position at seating height where visitors can touch and smell the leaves.
• Minimum pot size: 30–40 cm Ø, 15 L+
• Excellent drainage essential; add perlite
• Use free-draining potting compost with 20–30% perlite or grit
• Ensure drainage holes; stand on pot feet to prevent waterlogging
• Feed with dilute liquid fertiliser (half-strength) every 2–3 weeks in growing season
• Indoor: Place on brightest windowsill (south-facing ideal); supplement with grow lights in winter
Companion Planting
Place near seating areas for fragrance when leaves are brushed. The scented foliage adds aromatic interest to container groupings. Combine with other scented pelargoniums for a fragrance collection. The deeply cut leaves provide textural contrast with broader-leaved herbs.
| ✓ Good companions | Roses, Brassicas, Fruit trees |
| ✗ Avoid planting with | Mint (invasive neighbour) |
Common Mistakes to Avoid
Believing it will repel mosquitoes just by sitting on the patio (it won't — the oil must be released by crushing leaves). Paying premium prices for what is essentially a standard scented pelargonium with good marketing. Neglecting it once the mosquito-repelling novelty wears off — it's genuinely a lovely aromatic plant. Same overwintering failures as all pelargoniums.
Harvesting & Preservation
Harvest leaves for potpourri and sachets — the citronella scent is persistent when dried. Crush fresh leaves and rub on skin for a brief, mild citronella-like fragrance (though commercial repellents are far more effective). The leaves can be used in finger bowls at dinner — floating on water, they release a lemony fragrance.
• Time of day: Early morning, after dew has evaporated but before intense midday heat volatilises essential oils
• Growth stage: Just before flowering, when essential oil concentration peaks. Once flowers open, the plant redirects energy from leaf production
• Season: Year-Round
• Part harvested: Leaves
• Harvest rule: Never remove more than ⅓ of the plant at once; this ensures continued vigorous regrowth
• Technique: Cut stems cleanly above a leaf node with sharp scissors or secateurs. Tearing damages tissue and invites disease
| Method | Process | Shelf life | Best for |
|---|---|---|---|
| Air drying | Tie bundles, hang upside down in warm, dark, airy space | 6–12 months | Most herbs |
| Oven / dehydrator | Spread on trays, 35–45°C until crisp | 6–12 months | Fleshy-leaved herbs |
| Freezing (whole) | Blanch 5s, ice bath, pat dry, freeze flat on tray | 6 months | Basil, chives, parsley |
| Freezing (oil cubes) | Chop fine, pack into ice cube tray, cover with olive oil | 6 months | Any culinary herb |
| Herb salt | Layer herb and coarse salt 1:4, dry and grind | 12+ months | Rosemary, thyme, sage |
| Infused vinegar | Pack jar, cover with warm vinegar, steep 2–4 weeks | 6 months | Tarragon, dill, basil |
| Infused oil | Fill jar with dried herb, cover with oil, steep 4–6 weeks | 3–6 months | Rosemary, thyme, chilli |
Frequently Asked Questions
Does the mosquito plant actually repel mosquitoes?
Not significantly by merely growing near you. Research shows the intact plant releases insufficient volatile compounds to deter mosquitoes at typical sitting distances. Crushing leaves and rubbing on skin provides brief, mild repellence, but commercial citronella products are far more effective.
Is it genetically modified?
Despite 1990s marketing claims, it is not a GMO plant containing citronella grass genes. It's a naturally citronella-scented pelargonium, possibly hybridised through conventional means. The 'genetic engineering' claim was a marketing story, not science.
Is it worth growing?
Yes — just not for the reason it's usually sold. It's a genuinely attractive, aromatic foliage plant with deeply divided leaves and a pleasant citronella scent. Grow it as a scented geranium and enjoy it for what it is, not for what it was marketed as.
Seasonal Care Calendar
🌱 Spring (Mar–May)
Water: Regular
Feeding: Regular feeding
☀️ Summer (Jun–Aug)
Water: Heavy
Feeding: Heavy feeding
🍂 Autumn (Sep–Nov)
Water: Moderate
Feeding: Light feeding
❄️ Winter (Dec–Feb)
Water: Moderate
Feeding: Light feeding
The 'mosquito plant' — a scented pelargonium with citronella-like fragrance and deeply cut, lacy leaves. NOT an effective insect repellent by proximity alone (crushing needed). Tender (zones 10–11). Genuinely lovely aromatic foliage plant. Same care as rose geranium. Don't believe the hype.
Quick Reference: Pelargonium citrosum
Key Principles: Right location, well-drained soil, regular harvesting to promote growth, and appropriate winter protection for tender species.