Ornamental · Asteraceae
Zinnia
Zinnia elegans
Give it full sun and dry leaves, and the zinnia blooms hard from summer to frost.
Full sun
Every 5–7 days
68–86°F · 20–30°C
60–70 days
Overview
Zinnias are about the easiest flower a beginner can grow, and they pay back almost any effort. They belong to the daisy family and trace back to Mexico, where they grew wild long before gardeners around the world took them up. As a warm-season annual, a single packet of seed carries you from spring to the first hard frost.
The range runs wide. Some stay short and tidy at around 6 inches, perfect for the front of a bed, while the tall cutting types stretch to 4 feet and fill a vase for weeks. Bees and butterflies work the open flowers all day, and the more you cut, the harder the plant blooms.
Zinnias do ask for two things. They want full sun and dry leaves, since their main weaknesses are the mildew and leaf spots that move in on crowded, wet foliage. Give them room, water at the roots, and the trouble mostly stays away.
Care
The short version: full sun, well-drained soil, and water at the base about an inch a week. Space the plants so air moves through them, deadhead often, and they bloom from summer until frost.
Light
Zinnias need full sun, at least 6 hours of direct light a day and ideally more. Sun keeps the plants stocky and the blooms coming, and it dries the leaves fast, which is the single best defense against mildew.
Water
Water at the base in the morning and keep it off the leaves, since wet foliage is what invites disease. Give about an inch a week and let the top half of the soil dry between drinks, easing back once the plants settle in, as zinnias handle heat and drought well.
Soil
Plant in well-drained loam. Zinnias aren't fussy and take a pH anywhere from 5.5 to 7.5, but they hate wet feet, so good drainage matters more than rich ground.
Temperature
Zinnias thrive in warmth, happiest between 68°F and 86°F (20°C to 30°C). They sulk in cold soil and die at the first frost, which is why you wait for real warmth before sowing.
Humidity
These are low-humidity plants, most comfortable around 40% to 60%. Damp, muggy air encourages mildew and leaf spot, so airflow counts for more than any moisture in the air.
Feeding
Feed monthly through spring and summer with a balanced fertilizer. Zinnias are light feeders and bloom well in average soil, so don't overdo it.
Pruning
Deadhead spent blooms and cut flowers often to push fresh branching and keep the color coming. Pinch the young plants early too, and they grow bushier with far more buds.
Repotting
not_applicable
Size & spacing
Plants run from 1 to 4 feet (30 to 120 cm) tall depending on the type. Space them 6 to 12 inches (15 to 30 cm) apart so air moves freely and the leaves stay dry.
When to plant
Zinnias want warm soil and won't tolerate frost. Start seed indoors 4 to 6 weeks before the last frost or sow it straight into the ground once the soil warms, and the flowers carry on from midsummer right up to the first frost.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 4 to 6 weeks before the last frost
- Plant: After the last frost once soil warms to about 70°F (21°C)
- Harvest: Summer to first frost
Troubleshooting
Almost every zinnia problem shows up on the leaves and traces back to wet foliage. Catch the first spots early and you can stop a small patch before it spreads through the bed. Match what you see below, then act while it still does some good.
Reddish-brown spots with pale gray centers spreading on the leaves
Alternaria leaf spot is the most serious disease zinnias face, and it can ring a stem and wilt the whole plant once it gets going. The fungus rides in on splashing water and infected debris during warm, wet stretches. Pull and destroy sick plants, water at the base, rotate the bed so you don't replant zinnias in the same ground for two years, and treat seed in hot water before sowing.
Fix:
- Remove and destroy infected plants and debris
- Water at the base of plants and avoid overhead irrigation
- Rotate planting sites and avoid replanting zinnias in the same spot for 2 years
- Treat seed with hot water (125°F for 30 minutes) before sowing
White powdery dust on the tops of the leaves
This is powdery mildew, a fungus that takes hold when plants sit crowded in still, humid air. It rubs off the leaf at first, then turns the foliage yellow and ragged as late summer wears on. Open the planting up for airflow, water only at the base, and reach for resistant series like Profusion or Zahara next time around.
Fix:
- Improve spacing and air circulation
- Water at the base in the morning and avoid wetting foliage
- Remove and discard heavily infected leaves and end-of-season debris
- Choose resistant types such as the Profusion or Zahara series
Angular purple spots boxed in by the leaf veins
These hard-edged spots are bacterial leaf spot, and the straight sides come from the veins fencing the bacteria in. It rides on splashing water and clings to contaminated seed and old debris, so it flares after rain or overhead watering. Keep the foliage dry, clear away infected leaves, space plants so they dry fast, and start with clean seed and resistant types.
Fix:
- Avoid overhead watering and handling wet plants
- Remove infected leaves and plant debris
- Improve spacing so foliage dries quickly
- Start with disease-free seed and resistant cultivars
Toxicity
Good news for a pet-friendly garden: zinnias are non-toxic top to bottom. The ASPCA lists them as safe for cats, dogs, and horses, and the petals are even edible for people. A pet that nibbles a leaf might get a brief upset stomach, but there's nothing here that will do real harm.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe to be around. A curious cat that chews a leaf might have a brief upset stomach, nothing more.
Dogs None
No real risk here. A dog that nibbles the foliage may get a little loose in the gut, and that passes on its own.
Horses Safe
Listed as non-toxic, so grazing near zinnias is fine.
Rabbits Safe
Rabbits can sample the leaves and flowers without harm, though too much of any new green can loosen the stool.
Livestock Safe
Cattle, goats, and sheep aren't poisoned by zinnias, and the plants pose no grazing hazard.
Birds Safe
Birds are in no danger from the plant, and they happily pick at the ripe seed heads come fall.
People Safe
The petals are edible and turn up as a garnish in salads and on cakes. Nothing on the plant is toxic to people.
No special handling required; ingestion of plant material may still cause mild stomach upset in some pets.
Varieties
Zinnias come in everything from 6-inch dwarfs to towering cut-flower types. These are the ones worth knowing by name.
Benary's Giant
A tall cutting type reaching 36 to 42 inches with big, fully double, dahlia-like blooms that hold up beautifully in a vase.
State Fair
A vigorous tetraploid that climbs 3 to 4 feet and carries very large flowers.
Profusion
An interspecific Zinnia x hybrida series that shrugs off both leaf spot and powdery mildew.
Zahara
A Zinnia marylandica series bred for strong resistance to leaf spot and mildew.
Thumbelina
A dwarf, compact plant about 6 inches tall that suits edging and containers.
Queen Lime
A 30 to 40 inch series prized for its unusual lime-green and muted antique color blends.
How to propagate
Zinnias are among the simplest flowers to grow from scratch, and seed is far and away the best way to do it.
SeedEasy
Spring
Zinnias come up fast and easy from seed. Direct sow after the last frost once the soil warms to about 70°F (21°C), or get a jump by starting them indoors 4 to 6 weeks earlier. Tuck the seed about a quarter inch deep, hold it at 65°F to 70°F (18°C to 21°C), and it sprouts in roughly 5 to 7 days. Thin or space the seedlings so air moves freely, then pinch the young plants to push branching and a fuller flush of bloom.
Myths
Overhead watering keeps zinnias healthy and cool.
A sprinkle from above leaves the foliage wet, and wet leaves are exactly what powdery mildew, Alternaria, and bacterial leaf spot need to spread. Water at the base instead and let the leaves stay dry.
All zinnias get mildew the same, so the variety you pick makes no difference.
Variety choice matters a lot. The resistant series such as Profusion and Zahara fight off leaf spot and mildew far better than the older large-flowered types, which often look tattered by late summer.