Zinnias are the cut-flower gardener's best friend: they are easy from seed, they flower within weeks of sowing, and the more you cut them, the more they bloom. A bed of zinnias in mixed colours gives armfuls of flowers from midsummer until the first frost, and butterflies flock to them all season.
Zinnias come in every colour except blue, from neat little pompom types to giant dinner-plate blooms, and from dwarf edging plants to tall cutting varieties over a metre high. They want heat and sun and they hate cold, wet soil, so the single most important decision is timing: sow them only once the soil is genuinely warm, and they will reward you with months of flowers.
Zinnias at a glance
| Growing factor | What zinnias need |
|---|---|
| Sun | full sun |
| Soil pH | 6.0–7.0 |
| Days to germination | 5–10 |
| Days to maturity | 60–70 |
| Spacing | 8–12 inches apart |
| Water needs | moderate |
| Cold tolerance | tender |
| Family | Asteraceae |
Starting seeds
Zinnias give you a choice: start seeds indoors for earlier flowers, or sow direct once the soil warms. For the earliest display, sow indoors a few weeks before your last frost — late winter in Zones 3–5, early spring in Zones 6–8, late winter in Zones 9–10 — and transplant out after the frosts end. For direct sowing, wait until the soil is workable and warming: late spring in Zones 3–5, mid-spring in Zones 6–8, early spring in Zones 9–10. Zones 11–13 are frost-free, so both methods work through much of the year; check your local extension service for the best local dates. Seeds germinate in 5–10 days. Keep seed mix or soil evenly moist until seedlings are up, and give indoor seedlings as much light as you can. Our seed starting calculator plans your indoor sowing date, and the germination time calculator estimates when to expect seedlings.
Transplanting and planting out
Transplant seedlings out after the last frost, on a cloudy day or in the evening so they do not wilt in the sun. Space plants 8–12 inches apart — that spacing is what keeps air moving and disease down — and water each plant in well. Our plant spacing calculator works out exactly how many plants fit your bed, and the square foot garden planner helps lay them out.
Soil and feeding
Zinnias grow best in fertile, well-drained soil with a pH of 6.0–7.0. Dig in compost before planting — it feeds the soil and helps it hold moisture without getting soggy — and mulch after planting to keep the roots cool and the weeds down. Feed during the growing season with a balanced fertiliser at the label rate, roughly once a month while plants are actively growing, and stop feeding as the season ends. Our fertiliser calculator works out the right amount for your bed, and the compost ratio calculator helps you make good compost to dig in.
Watering
Zinnias have moderate water needs: keep the soil evenly moist while plants are establishing and flowering, and water deeply rather than little and often so the roots grow down. Water at the base in the morning so the foliage dries during the day, mulch to hold moisture in, and watch for wilting in hot, dry spells. Our watering calculator gives a starting point for your bed size, and the watering schedule generator can build a routine around it.
Sunlight and temperature
Zinnias need full sun — at least six hours of direct sun a day. Zinnias are tender — frost kills them or damages them badly, so they are grown as warm-season plants in most zones and planted out only once frosts are over. In frost-free Zones 11–13 they can grow for much of the year. Use the frost date calculator to find your last frost date. Our sunlight calculator can check whether your spot gets enough sun.
Pests and diseases
The pests and diseases to watch for on zinnias are aphids, slugs, thrips. Aphids and slugs are the usual pests, and thrips can mark the petals in hot, dry weather. Good air flow helps more than anything, so do not crowd zinnias. Check plants weekly, looking under leaves as well as on top, and act early. Hand-pick larger pests, knock aphids off with a strong spray of water, and remove badly affected leaves. Keep the area weed-free and avoid wetting the foliage when you water, since damp leaves invite fungal disease. Our pest identifier helper can help identify what you are seeing, and the plant disease checker helps narrow down leaf and stem problems.
Companion plants
Good companions for zinnias are lavender, marigolds, garlic, chives. Lavender, marigolds, garlic and chives all sit well with zinnias, and marigolds in particular help keep soil pests down around the bed. Our companion planting finder can suggest more pairings for your bed plan.
Harvesting
Cut zinnias for the vase when the flowers are fully open and the stem feels stiff when you wiggle it — a flower whose stem bends is not ready and will wilt in the vase. Cut in the morning, strip the lower leaves, and put stems straight into water. Regular cutting is the secret to more flowers: a zinnia that is left to set seed slows down, while a zinnia that is cut weekly keeps blooming until frost. Our harvest date calculator can estimate your picking date from your sowing date, and the vegetable yield estimator helps you work out how much a bed will produce.
Common problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Powdery mildew | damp leaves and poor air flow | Water at the base, space plants properly, and remove affected leaves. |
| Leggy plants with few flowers | too little sun or sown too early in cold soil | Sow only in warm soil and full sun, and pinch out the tips of young plants. |
| Flowers wilt in the vase | cut too young | Cut only when the stem is stiff, and put stems in water immediately. |
Powdery mildew
White powdery patches on zinnia leaves are the most common problem, and they spread fast in still, damp air. Water at the base in the morning, keep to the spacing in the table, and pick off the worst leaves as soon as you see them.
Leggy plants with few flowers
Zinnias sown in cold soil sulk, and zinnias in shade stretch for the light and flower poorly. Wait for warm soil, give them full sun, and pinch out the growing tips of young plants to make them branch and flower more.
Flowers wilt in the vase
A zinnia stem that is still soft and bendy will flop in the vase within hours. Use the wiggle test: hold the stem a few inches below the flower and wiggle it — if the flower stays firm and upright, it is ready to cut.
Frequently asked questions
How long does it take to grow zinnias?
From planting to maturity takes 60–70 days. Seed germination takes 5–10 days, and the total time depends on whether you start from seed, a nursery plant, or a bulb or cutting.
How far apart should I plant zinnias?
Space zinnias 8–12 inches apart. That spacing gives each plant room for air movement, which keeps disease down, and room to reach its full size without crowding its neighbours.
What soil pH do zinnias need?
Zinnias prefer a soil pH of 6.0–7.0. Test your soil before amending it — most garden soils are close enough, and guessing with lime or sulphur can do more harm than good.
Do zinnias come back every year?
No, zinnias are annuals: they flower for one season and are killed by frost. They self-seed freely in warm gardens, though, so you may find seedlings next spring if you let some flowers go to seed.
How do I get bushier zinnias?
Pinch out the growing tip of each young plant when it has three or four pairs of leaves. The plant will branch out, giving you more stems and more flowers, though the first blooms will be a little later.