Germination temperature
About 18-24 °C (65-75 °F); sources differ slightly within this range.
Flower growing guide
Zinnias love heat and come up in 5-7 days in warm soil, which makes them one of the most reliable summer flowers from seed. This guide covers sowing depth, transplanting, and how to keep mildew and leaf spots off the leaves.
About 18-24 °C (65-75 °F); sources differ slightly within this range.
About 6 mm (1/4 in), covered.
5-7 days.
Darkness: cover the seed.
None needed.
Direct sowing in warm soil is easiest; transplant young seedlings carefully.
Zinnia seeds are flat, arrow-shaped and easy to handle. Sow them individually or two to a spot and thin to the stronger seedling.
Not needed. The seed absorbs water readily.
Not needed. Zinnia is a warm-season annual with no cold requirement; it simply waits for warm soil.
Not needed. Sow into moist, warm soil.
Extension sources give 18-21 °C (65-70 °F) up to about 21-24 °C (70-75 °F). Zinnias do not germinate well in cold soil, so outdoors sow only after the weather has warmed.
Cover the seed with about 6 mm (1/4 in) of soil or seed compost.
Fertile, well-drained soil in full sun. Zinnias do not like waterlogged ground.
Keep the soil evenly moist until emergence, then water at the base of the plants rather than over the leaves.
Zinnia needs darkness to germinate (Iowa State University), so make sure every seed is covered.
About 5-7 days in warm conditions.
If you start seed in trays, sow 4-6 weeks before planting out. Zinnias grow quickly, so do not let them become root-bound, and disturb the roots as little as possible.
Space plants generously so air can move between them; good airflow is the main defence against powdery mildew. Give tall cutting types more room than compact bedding types.
When young plants have several pairs of leaves, pinching out the tip gives more branches and longer flowering stems for cutting.
Cause: powdery mildew, common in humid weather. Fix: space plants for airflow, water the soil not the leaves, and remove badly affected leaves.
Cause: Alternaria leaf spot, which also spreads on seed. Fix: keep foliage dry, rotate zinnias to a new bed for a year or two, and clear all plant debris at the end of the season.
Cause: bacterial leaf spot, encouraged by wet foliage. Fix: water early in the day at the base of plants and avoid working among wet plants.
Cause: cold, wet soil. Fix: wait until the weather is warm, or start seed in trays at about 21 °C (70 °F).
Zinnias thrive in hot, dry conditions. In the Indian plains sow them as the weather warms after winter for summer flowers, and again before the rains; very wet monsoon weather encourages leaf diseases. In the hills, sow in late spring after frosts.
Taller zinnias make excellent cut flowers. Regular cutting or deadheading keeps new flowers coming.
Double mixes give a range of colours and flower forms; some plants may carry semi-double or single flowers. Remove the plainer ones early if you want a uniform bed.
Leaf spot diseases can be carried on seed, so do not save seed after a leaf spot outbreak.
Sow double zinnias for a bright, heat-loving summer bed and long-lasting cut flowers.
No. Zinnias germinate in darkness. Cover the seed with about 6 mm (1/4 in) of soil and keep it moist and warm.
That is powdery mildew, common in humid weather. Give plants more space, water at the base early in the day, and choose mildew-resistant varieties if it is a regular problem.
Yes, if they are moved young, before roots fill the pot. Sow trays 4-6 weeks before planting out, or simply sow directly in warm soil.
Pinch young plants once for more branches, cut flowers regularly with long stems, and keep plants in full sun with good airflow so the leaves stay healthy through the season.