How to Grow Zinnia -- Garden Chronicle (2024)

Get to know Zinnia

Plant type: Annual
Growing Zones and range: Annual in all zones
Hardiness: Tender
Height and width: 12 to 24 inches (30-61cm) tall; 6 to 15 inches (15-38cm) wide
Foliage: Leaves range from linear to ovate or rounded
Flowers: Showy daisylike flowers can be single or double; the flowerheads of some resemble formal decorative dahlias (referred to as “dahlia-flowered”), others resemble cactus-flowered dahlias (referred to as “cactus-flowered”)
Flower colors: Shades of orange, red, bronze, hot pink, orange-red, and yellow-orange as well as white, pale pink, cream, and green
Bloom time: Summer to frost
Uses: Cut flowers, beds, borders; compact hybrids; taller varieties for cutting; containers; zinnias attract hummingbirds and butterflies
Common name: Zinnia
Botanical name: Zinnia spp.
Family: Asteraceae
Origin: Primarily Mexico, also southwestern North America, and parts of Central and South America

Plant zinnias in full sun in Zones 2-8. Plant zinnias in light shade in hot-summer regions in Zones 9-11.
Grow zinnias in humus-rich, well-drained, neutral to acidic soil.
Planting zinnias where there is good air circulation will stem attacks by pests and diseases.

Set zinnias in the garden in spring after all danger of frost has passed.
Sow seeds indoors 6 to 8 weeks before the last frost; sow seeds at 60° to 65°F (15.6-18°C).
Transplant zinnias to the garden with care a week or two after the last frost in spring.
For season-long blooms, sow seeds every 3 to 4 weeks until mid-summer.

Space zinnias 6 to 15 inches (15-38cm) apart depending on the variety.
Sow seed 1/4 inch deep in sterile seed starting mix indoors; sow seed outdoors in evenly prepared garden soil.

Zinnias need moderate moisture; keep the soil evenly moist.
Fertilize zinnias occasionally every 4 to 6 weeks with an all-purpose fertilizer.
Zinnias are prone to mildew; avoid wetting leaves and select mildew-resistant varieties.

Mulch around zinnias to conserve moisture and stem the spread of disease in splashing water.
Pinch the ends of growing tips to encourage fuller plants. Do not pinch plants if you are growing zinnias for cut flowers and want long-stemmed flowers.
Stake tall plants as needed.

Aphids, capsid bugs, chrysanthemum eelworms, and earwigs may attack zinnias.
Seedlings are susceptible to damping off and in wet conditions fungal root rots.
Grey mold may infect the flowers in wet seasons.
Powdery mildew can settle on leaves in cool or wet weather.

Zinnia seeds germinate in 7 to 10 days at 70° to 80°F (21°-27°C).
Sow seeds indoors or in a greenhouse in spring 6 weeks before transplanting them to the garden.
Sow seed outdoors after the last frost in spring; sow seed in final planting position and thin out the seedling to the required spacing.
Zinnias do not like roots being disturbed at transplant time.

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Zinnia angustifolia: Annual, compact plants to 16 inches (40cm) tall; inch-wide flower hears; bloom in 6 weeks from seed; perennial in mild winter; can be used in hanging baskets.
Z. elegans: Annual grows 12 to 36 inches (30-91cm) tall; flower heads from 1 to 7 inches (2.5-17cm) across; forms include full doubles, cactus flowered, and crested; colors in white, pink, salmon, rose, red, yellow, orange, lavender, purple, and green; strains include Border Beauty, Burpeeana California Giants, Ruffles, State Fair, Zenith.
Z. grandiflora: Perennial in warm-winter regions, grows to 10 inches tall, flowerheads 1.5 inches across.
Z. haageana: Annual, compact plants to 18 inches (45cm) tall, flowers in red, yellow, and orange, long-blooming.