Sowing: March to July
Zinnias grow quickly and may bloom in just 45 days. Successive sowing every few weeks beginning from April through early July will ensure continuous flowering throughout summer, from July to first frosts.
Sowing Indoors: March to April
For early flowers, start indoors four to six weeks before the last frosts are expected. Use trays or pots and a good sowing compost. Seeds should be spaced at least 2.5cm (1in) apart. The seeds need light to germinate, so “just cover” the seeds with a sprinkling of fine, sieved soil. Seeds will germinate in 7 to 14 days. Keep soil moderately moist during germination.
When plants are 3 to 5cm (1 to 2in) in height, transplant to 7cm (3in) pots and grow on. Zinnias are sensitive to root disturbance, so be especially careful when transplanting. Gradually acclimatise indoor started seedlings outdoors after all danger of frost has passed and weather has warmed considerably. Plant out 25 to 30cm (10 to 12in) apart. Add garden compost to the soil if it is heavy or infertile.
Sowing Direct: April to July
Sow seeds where the plants are to be grown in spring after the last frost, and in an area with full sun. Zinnia prefers fertile, rich, and well-drained soil, average soil is acceptable, but if you add compost and all-purpose fertiliser before sowing, the blooms will be lusher.
Sow seeds 5 to 7cm (2 to 3in) apart in rows 30cm (12in) apart. Barely cover seeds with soil; they need light to germinate. Keep soil moist until seeds germinate, in 5 to 10 days. When 5cm (2in) tall thin the seedlings to 25 to 30cm (10 to 12in) apart.
