Sow thinly, 12mm (Â½in) deep in drills 45cm (18in) apart in well cultivated soil which has been raked to a fine tilth. Germination usually takes about 21 days. When large enough to handle, thin out seedlings to 45cm (18in) apart. Alternatively, sunflowers can be sown indoors in late winter/early spring. Sow individually into 7.5cm (3in) pots at a temperature of 20-30Â°C (68-86Â°F). Grow on in good light and plant out when all risk of frost is passed.