How to Grow Ulam Raja
Cosmos caudatus
Ulam raja (Cosmos caudatus) is a vigorous SE Asian salad herb grown for its tender young leaves, not its flowers. It needs warmth and full sun — sow indoors at 22-30°C and plant out only after nights stay reliably above 18°C. Space plants generously at 40 cm for air circulation. Pinch tips regularly to keep growth bushy and prevent premature flowering, which reduces leaf quality. Harvest young leaves and shoot tips frequently; the mild, slightly anise-flavoured leaves are eaten raw in salads and as a garnish throughout SE Asian cuisine. Grows fast in heat and can reach 1.2 m if left unpruned.
When to Start
Start seeds indoors 3 weeks before your last frost date. Transplant outdoors once night temperatures stay above 15°C and soil has warmed to at least 20°C.
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Growth Stages
Approximate days from start
Care Essentials
- Light balanced liquid feed every 2 weeks during active growth. Avoid high nitrogen, which encourages leaf quantity but reduces flavour intensity.
- A SE Asian salad herb distinct from ornamental Cosmos bipinnatus. The entire young plant is edible. Rich in antioxidants and traditionally used in Malay and Indonesian cuisine. Thrives in tropical heat but can be grown as a summer annual in temperate climates with protection.
Growing Conditions
- Min. soil temperature
- 20°C+
- Germination temperature
- 22–30°C
Pet Safety
- Sow indoors
- —
- Transplant out
- —
- First harvest
- —
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Spacing & Planting
| Plant spacing | 40 cm |
| Row spacing | 50 cm |
| Sow depth | 0.5 cm |
| Mature height | 250 cm |
| Mature spread | 60 cm |
Ulam raja grows vigorously and needs space for air circulation. Plant 40 cm apart in rows 50 cm apart. Closer spacing leads to leggier growth and fungal issues in humid conditions.
Growing Conditions
| Min. soil temperature | 20°C |
| Germination temperature | 22–30°C |
| Base growth temperature | 15°C |
| Min. daylength to start | 10h |
| Photoperiod sensitivity | day neutral |
Frequently Asked Questions
- How far apart should I plant Ulam Raja?
- Plant Ulam Raja 40cm apart with 50cm between rows.
- When can I harvest Ulam Raja?
- Ulam Raja is ready to harvest approximately 35 days after transplanting.
- Is Ulam Raja frost hardy?
- Ulam Raja is classified as Tender.
