Cosmos
Thrives on neglect in poor, dry soil - rich, over-fed ground produces lush leaves but far fewer flowers. Seedlings resent root disturbance, so raise in trays and transplant young or sow direct once frost risk has passed.
- Sun
- full sun
- Water
- low
- Spacing
- 30cm
- Difficulty
- beginner
- Grows in
- Whangārei / Northland, Auckland, Hamilton / Waikato, Tauranga / Bay of Plenty, Gisborne, Napier / Hawke's Bay, New Plymouth / Taranaki, Palmerston North / Manawatū-Whanganui, Wellington, Nelson, Tasman, Blenheim / Marlborough, West Coast, Christchurch / Canterbury, Dunedin / Otago, Invercargill / Southland
- Mature height
- 1.2m
- Flowering season
- Jan, Feb, Mar, Dec
- Attracts wildlife
- Butterflies
- Common diseases
- Powdery mildew, Grey mould (botrytis)
- Common pests
- Aphids, Thrips
When to plant by region
In Whangārei / Northland, Auckland, Tauranga / Bay of Plenty, Gisborne and Napier / Hawke's Bay: September-November. In Hamilton / Waikato, New Plymouth / Taranaki, Palmerston North / Manawatū-Whanganui, Wellington, Nelson and Tasman: October-November. In Blenheim / Marlborough, West Coast and Christchurch / Canterbury: October-December. In Dunedin / Otago and Invercargill / Southland: November-December.
Growing stages
Germination & planting
- Sow direct once frost risk has passed, or raise in trays and transplant while still young, as seedlings resent root disturbance
- Avoid rich, over-fed soil; cosmos actually flowers best in poor, dry ground
Establishment
- Water sparingly; cosmos thrives on some neglect once seedlings are settled in
- Watch for aphids and thrips on soft new growth
Vegetative growth
- Tall, airy growth to around 120cm; resist the urge to feed, as lush over-fed plants produce fewer flowers
- Grey mould (botrytis) can develop in damp, crowded conditions
- Powdery mildew may appear on leaves later in the season
Flowering
- Deadhead regularly to extend the flowering display
- Butterflies visit the blooms, so avoid spraying insecticide on open flowers