Zinnia
Zinnia elegans
Zinnias are showy half-hardy annuals from Mexico, producing bold, double or semi-double flowers in an extraordinary range of colours from July to October. Their stiff, upright stems make them outstanding cut flowers that last up to two weeks in a vase. Heat-loving and drought-tolerant, they perform best in the warmest, sunniest spots in UK gardens. Flower forms range from neat pompons to large cactus-flowered types over 12 cm across.
How to grow zinnia
Sow seed indoors in April at 18-21 degrees Celsius in individual modules — zinnias dislike root disturbance. Seeds germinate in 5-7 days. Harden off and plant out after the last frost in late May or early June, spacing 25-30 cm apart. Choose the hottest, most sheltered spot in the garden with fertile, well-drained soil. Water at the base of the plant rather than overhead, as wet foliage encourages powdery mildew. Feed fortnightly with a high-potash liquid fertiliser once buds form. Deadhead regularly to prolong flowering. For cut flowers, harvest when petals are fully open and feel firm to the touch. Pinch out the central growing tip when plants are 15 cm tall to encourage branching and more stems for cutting. Dwarf varieties such as Profusion and Zahara are ideal for containers and bedding in cooler UK summers.
Pruning
Pinch out the central growing tip at 15 cm to promote branching. Deadhead spent flowers regularly. No other pruning required.
Propagation
- Seed (sow indoors April, plant out after last frost)
Common problems
- Powdery mildew
- Alternaria leaf blight
- Aphids
- Slugs on young plants
- Poor performance in cool, wet summers
Good companions
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