edenhana

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.

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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

  1. 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

  2. Establishment

    • Water sparingly; cosmos thrives on some neglect once seedlings are settled in
    • Watch for aphids and thrips on soft new growth

  3. 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

  4. Flowering

    • Deadhead regularly to extend the flowering display
    • Butterflies visit the blooms, so avoid spraying insecticide on open flowers

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