Timing
Direct sow after last frost, in April and May on the coast. Zinnias don’t transplant well, but you can try starting some indoors in peat or coir pots 6-8 weeks before planting out. Maintain a soil temperature of 21-26°C (70-80°F). Seeds should germinate in 5-24 days.

Starting

Just cover Zinnia seeds, and aim for a final spacing of 25-30cm (10-12″) between plants.