Persicaria odorata (Vietnamese Coriander (Rau Ram))
Persicaria odorata (Vietnamese Coriander (Rau Ram))
Contents
Introduction & History
Vietnamese coriander smells exactly like cilantro — but it's not even remotely related. This trailing, tropical knotweed (Polygonaceae, not Apiaceae) fills the same flavour niche in Southeast Asian cooking that cilantro fills in Latin American cuisine, and it thrives in the steamy heat where true coriander bolts and dies within a week. For anyone who loves cilantro but lives in a hot climate, or who finds the flavour of coriander seeds too mild, rau răm is the perfect solution. The arrow-shaped leaves with their dark chevron markings are as handsome as they are useful.
History & Origin
Native to mainland Southeast Asia — Vietnam, Thailand, Laos, Cambodia, Malaysia, and southern China. A staple of Vietnamese cuisine for centuries, where it appears in phở, gỏi cuốn (fresh spring rolls), and laksa. Also used in Thai, Malay, and Singaporean cooking. Known by many names: rau răm (Vietnamese), daun kesum (Malay), pak phai (Thai), and hot mint. Introduced to tropical gardens worldwide by Southeast Asian diaspora communities.
Botanical Description
Trailing to semi-upright perennial, 15–40 cm tall, spreading widely by rooting stems. Leaves are lanceolate, 5–8 cm long, pointed, with a distinctive dark V-shaped chevron marking on the upper surface. The foliage is smooth, slightly fleshy, and releases a powerful cilantro-citrus aroma when bruised. Small, inconspicuous pink flower spikes appear but rarely set seed outside the tropics. The stems are jointed, as typical of the knotweed family.
Stem: Semi-woody to woody at base • Height: 30 cm at maturity • Spread: 60 cm • Foliage: green with chevron marks • Flowers: pink (rarely) (rarely flowers)
Planting & Cultivation
Almost never grown from seed (it rarely sets seed in cultivation). Plant rooted cuttings or divisions in rich, moist soil, 20–30 cm apart. Prefers partial shade — it grows naturally at pond edges and in moist, shaded spots. In temperate climates, grow in containers and bring indoors before frost. Water generously; this is a moisture-loving plant.
| Sun exposure | Partial Shade |
| Soil pH | 5.5-7.0 |
| Spacing | 60 cm |
| Seed depth | 3–6 mm (surface-sow if light-dependent germinator) |
| Water needs | High |
| Soil type | Well-drained, humus-rich loam; add perlite or grit for drainage |
Cultivation Details
Keep consistently moist — Vietnamese coriander wilts rapidly in dry conditions and never fully recovers from severe drought. Feed monthly with liquid fertiliser for lush leaf growth. Trim regularly to maintain compact growth and prevent the stems from becoming leggy and woody. In tropical climates, it can be invasive by stolons — contain with barriers or grow in pots. Afternoon shade in hot climates prevents leaf scorch.
Climate & Hardiness
Tropical to warm-temperate perennial in zones 9–12 outdoors. Frost-tender — killed below 0 °C. In zones 7–8, grow as a summer annual or overwinter indoors on a sunny, humid windowsill. Thrives in heat and humidity (25–35 °C). The plant grows fastest in warm, moist, semi-shaded conditions mimicking a tropical stream edge.
USDA zones: 9-11
Minimum temperature: 0°C
Indoor growing: Suitable for windowsill culture with 6+ hours light
Seasonal Care
Spring: plant outdoors after last frost or move overwintered pots outside. Summer: peak growth — harvest frequently, water generously, feed monthly. Autumn: before first frost, pot up garden plants for indoor overwintering. Trim back by half. Winter: indoors, place in bright indirect light, keep moist, reduce feeding. Growth slows but the plant remains alive.
Propagation
Stem cuttings root in water within 5–7 days — the easiest propagation method imaginable. Cut 10–15 cm stems, strip lower leaves, place in a glass of water on a windowsill. Pot up when roots are 3–5 cm long. Division of established clumps in spring is equally simple. Layering happens naturally — stems touching moist soil root at every node. Seed is rarely available.
| 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
Slugs and snails are the main outdoor pests — the soft, fleshy foliage is irresistible to them. Use beer traps, copper tape, or slug pellets. Whitefly and spider mites may appear on indoor plants in winter — mist regularly and use yellow sticky traps. Root rot occurs only in completely waterlogged (stagnant) conditions — despite liking moisture, it needs some drainage. No significant diseases.
Culinary Uses
Essential in Vietnamese, Malaysian, and Singaporean cuisine. The classic pairings: duck egg balut (Philippines), laksa (Malaysia/Singapore), fresh spring rolls (Vietnam), and as a garnish for phở. The flavour is often described as 'cilantro plus pepper plus citrus.' In Southeast Asian salads, tear the leaves and toss with shallots, chillies, and lime juice. The leaves also pair well with duck, fatty pork, and seafood, where their peppery bite cuts richness.
Medicinal & Aromatherapy
Traditional Vietnamese and Malay medicine uses rau răm for digestive complaints, flatulence, and as an appetite stimulant. The plant contains flavonoids and aldehydes responsible for its aroma. In Vietnamese folk tradition, it is said to reduce sexual desire (perhaps explaining its nickname 'monk's herb'). No significant modern clinical research. Generally safe in culinary quantities.
Container & Companion Growing
Container Growing
Ideal for containers — especially important in temperate climates where overwintering is necessary. Use a 20–25 cm pot with moisture-retentive mix. Place in bright indirect light (not intense afternoon sun). Water frequently — this plant should never dry out. Feed every two weeks. The trailing stems drape attractively over pot edges. Bring indoors at 10 °C for winter.
• Minimum pot size: 20–25 cm Ø, 5 L+
• Warmth-loving; consider windowsill in winter
• 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
Pairs naturally with other moisture-loving Asian herbs: water spinach, taro, and rice paddy herbs. In the kitchen garden, grow alongside Vietnamese mint, Thai basil, and lemongrass for a complete Southeast Asian herb collection. The trailing habit makes it a good ground cover under taller plants in moist, shaded beds.
| ✓ Good companions | Eggplant, Peppers, Beans |
| ✗ Avoid planting with | Fennel, Dill (cross-pollinates) |
Common Mistakes to Avoid
Letting the soil dry out — Vietnamese coriander is not drought-tolerant. Growing in full, intense sun when it prefers partial shade. Not trimming regularly, allowing the plant to become leggy and woody with poor leaf quality. Expecting it to survive frost — it won't. Confusing it with true coriander/cilantro (completely unrelated, different family).
Harvesting & Preservation
Pick leaf tips and young stems at any time — the youngest leaves have the strongest flavour. Use fresh within a day or two; the leaves bruise and darken quickly. Does not dry well — the flavour vanishes. Freezing is possible but the texture suffers. The best preservation: keep a living plant on a windowsill year-round for continuous fresh harvest.
• 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 Vietnamese coriander taste like cilantro?
Very similar but not identical — rau răm has a more peppery, complex flavour with citrus and slightly soapy notes. People who dislike cilantro (the aldehyde-sensitive trait) may or may not enjoy Vietnamese coriander — it contains different aromatic compounds.
Can it replace cilantro in recipes?
In Southeast Asian dishes, it's the authentic choice — cilantro is actually the substitute. For Mexican or Indian dishes, it can fill in but the peppery note is different. Experiment to see if you like the swap.
Why is it called Vietnamese coriander if it's not coriander?
Because it fills the same culinary role and has a similar aroma. The 'coriander' name is purely about function and flavour, not botany. It belongs to the buckwheat family (Polygonaceae), not the carrot family (Apiaceae).
Seasonal Care Calendar
🌱 Spring (Mar–May)
Water: Regular
Feeding: Regular feeding
☀️ Summer (Jun–Aug)
Water: Very Heavy
Feeding: Heavy feeding
🍂 Autumn (Sep–Nov)
Water: Regular
Feeding: Light feeding
❄️ Winter (Dec–Feb)
Water: Moderate
Feeding: Light feeding
A trailing, tropical knotweed that tastes like cilantro but thrives in heat where coriander bolts and dies. Essential in Vietnamese and Malaysian cooking — phở, laksa, and spring rolls all depend on it. Roots from cuttings in a glass of water. Keep moist, keep picking, keep eating.
Quick Reference: Persicaria odorata
Key Principles: Right location, well-drained soil, regular harvesting to promote growth, and appropriate winter protection for tender species.