When to plant
Sow sunflower seeds outdoors in mid- to late spring once the risk of frost has passed. In cooler climates, start seeds indoors 3–4 weeks earlier and transplant after the soil warms. Avoid sowing too early outdoors, as cold soil delays germination.
Where to plant
Choose a sunny, open position with at least 6–8 hours of direct sunlight per day. Helianthus grows well in borders, vegetable patches, cutting gardens and children’s gardens. Tall varieties may need staking, so avoid very exposed, windy sites.
Preparing the soil
Loosen soil to 20–25 cm deep and enrich with compost. Sunflowers prefer fertile, free-draining soil that retains some moisture. Improve sandy soil with compost; lighten clay with organic matter. Avoid overly rich nitrogen fertilisers, which produce tall plants with fewer flowers.
Preparing the seeds
Sunflower seeds need no special treatment. Keep them dry and cool until sowing. If starting indoors, use deep pots or modules to avoid root disturbance, as sunflowers dislike transplant shock.
Sowing the seeds
Plant seeds 1.5–2.5 cm deep. Space tall varieties 40–60 cm apart, and dwarf or branching varieties 25–35 cm apart. When sowing indoors, transplant carefully, keeping the rootball intact.
After planting
Keep soil lightly moist until seedlings emerge. Protect young seedlings from slugs and birds. For tall varieties, place canes or supports early so roots are not disturbed later.
During growth
Water regularly—sunflowers prefer consistent moisture, especially as they grow rapidly. Mulch around the base to conserve moisture. Feed lightly once stems begin to elongate. Pinch out the growing tip of branching varieties to encourage multiple blooms.
After flowering / end of season
Cut flowers for vases or leave them on the plant to set seed. Once seedheads mature and dry, harvest seeds for roasting or leave them for birds. Remove spent stems in late autumn and compost them.
Extra tips
Plant in groups for maximum impact and stronger wind resistance. Sunflowers make excellent cut flowers, with long-lasting blooms. Smaller varieties are ideal for pots, balconies and children’s gardens.
