How to grow zinnia
Overview
Zinnia elegans is a fast-growing, warm-season annual from the Asteraceae family, grown for its vivid, long-lasting flowers and strong pollinator appeal. It thrives in heat and full sun, and needs regular deadheading to keep blooming through summer and autumn.
Varieties
- Zinnia elegans 'Benary's Giant' — Large, double flowers on strong stems; a favourite for cut-flower growers in Australia.
- Zinnia elegans 'Profusion' — Compact, heat- and mildew-tolerant series; ideal for garden beds and pots.
- Zinnia elegans 'Zahara' — Dwarf, weather-resistant hybrid with bright single flowers; excellent for borders.
Soil Preparation
Zinnia prefers neutral to slightly acidic soil (pH 6.0–7.0) with good drainage. Before planting, work in 2–3 cm of well-rotted compost or aged manure to boost organic matter. Avoid heavy clay or waterlogged beds—raise the planting area if drainage is poor.
Growing Guide
Sow zinnia seed directly 6 mm deep in well-drained soil after all frost risk passes, spacing 25–30 cm apart. For bushier plants, pinch out the first set of true leaves when seedlings are 15 cm tall. Water at the base to avoid wetting foliage, and feed with a balanced liquid fertiliser every 2–3 weeks. In subtropical and tropical zones, sow in late summer for an autumn–winter flower crop.
Sowing
Sow zinnia seed directly 6 mm deep, 25–30 cm apart, in warm soil after frost. Germination takes 5–10 days at 20–25°C. For earlier blooms, start in punnets and transplant when 10 cm tall, but direct sowing is simpler and produces sturdier plants.
Care
Feed zinnias with a balanced liquid fertiliser every 2–3 weeks during active growth. Deadhead spent flowers regularly to prevent seed set and encourage continuous blooming. Pinch out the first few buds to promote bushier plants with more stems.
Companion Planting
Zinnia is an excellent companion for cosmos, marigold, and basil, which share its sun and moisture needs and help repel pests. Avoid planting near potatoes or cucurbits, as zinnia can attract aphids that may spread to these crops.
Common Pests & Risks
Powdery mildew is common in humid or crowded conditions—space plants well and water at the base. Aphids and caterpillars can be controlled with a strong water spray or pyrethrum; treat early to prevent damage to flower buds.
Harvesting
Cut zinnia stems when the flower is fully open but before the centre cone starts to brown. Harvest early in the morning, strip lower leaves, and place in clean water immediately. Regular cutting encourages more blooms and extends the flowering season.
Troubleshooting
Yellow lower leaves: overwatering or poor drainage—reduce water and improve soil. Stunted growth: cold soil or late frost—wait for consistent warmth. White powdery coating on leaves: powdery mildew—increase air flow, avoid overhead watering. Holes in petals: caterpillars or earwigs—handpick or use pyrethrum. Flowers fading early: lack of deadheading—cut regularly to keep blooms coming.