How to Grow Zinnias from Seed (Zinnia elegans)

Few flowers give as much for as little as the zinnia. Sow a pinch of seed in late spring and within ten weeks you have stiff, upright stems topped with flowers in almost every colour except blue — and the more you cut, the more they flower, right up to the first frost. Zinnias come from the warm, dry uplands of Mexico, which tells you everything about growing them: they want heat, sun and good drainage, and they hate cold, wet starts. This guide covers how to grow zinnias (Zinnia elegans) from seed: when to sow, how to raise sturdy seedlings, planting and pinching, keeping powdery mildew at bay, and cutting for the vase.

• Sow Late April–mid May indoors at 21–24 °C · or direct from late May once the soil is warm
• Germination 4–7 days · cover lightly, about 5 mm deep
• Plant out Early June, after the last frost · full sun, 20–25 cm apart (15 cm for dwarf types)
• Flowers 8–10 weeks after sowing · July until the first frost · cut-and-come-again

What zinnias are — and why timing matters more than effort

Zinnias are half-hardy annuals in the daisy family, named after the 18th-century German botanist Johann Gottfried Zinn. Almost all garden zinnias are forms of Zinnia elegans: the tall, double "dahlia-flowered" and Giants of California types for cutting, the pompon-like Lilliput and dwarf Thumbelina for pots and edging, and novelties such as the chartreuse 'Envy' or the striped 'Peppermint Stick'. Two smaller relatives, Zinnia haageana (Persian Carpet) and Zinnia angustifolia (narrow-leaved or creeping zinnia), make bushy, free-flowering plants that shrug off heat and disease.

The single most important fact about zinnias is that they cannot take cold. Seedlings that sit in chilly, wet compost stall and rot; plants set out into cold May nights sulk for weeks and are overtaken by later sowings. That is why zinnias are never sown in autumn, unlike the hardy annuals you can sow now — they are a late-spring job. You will find them in the summer columns of our flower sowing calendar, alongside cosmos and sunflowers.

When to sow zinnia seeds

In most of Britain the sweet spot is late April to mid May indoors, for planting out in early June. Some of our packets list March, and you can sow that early if you have a heated greenhouse and good light — but zinnias that outgrow their pots before it is warm enough to plant them out often check and never fully recover. A month-old plant going into warm soil beats a two-month-old one held back in a cramped pot.

Direct sowing works well from late May into June, once the soil has warmed and night temperatures stay above about 10 °C. Direct-sown zinnias flower a little later but are often sturdier, because their roots are never disturbed. A final sowing in mid June gives fresh plants for September cutting, when the first ones are starting to tire.

How to sow zinnias, step by step

1. Sow in cells, not seed trays Zinnias resent root disturbance, so sow straight into modules, root trainers or 7 cm pots filled with seed compost. Two seeds per cell is plenty; the seeds are large and easy to handle.
2. Cover lightly and keep warm Push each seed about 5 mm deep, water from below and keep at 21–24 °C — a propagator or a warm windowsill. Seedlings usually appear in four to seven days; if nothing shows after two weeks, our guide on how to germinate seeds will help you find out why.
3. Give full light straight away Move the seedlings into the brightest spot you have the moment they emerge, and grow them on at 16–20 °C. Thin to the strongest seedling per cell. Zinnias stretch quickly in poor light and wet compost invites damping off, so water sparingly.
4. Harden off for a week or two From late May, put the plants outside by day and bring them in at night. Our guide to hardening off seedlings explains the routine. Do not rush it: a cold snap undoes the work.
5. Plant into warm soil in full sun Plant in early June, 20–25 cm apart for tall cutting types and about 15 cm for dwarf ones, in free-draining soil that is not over-rich. Water in well and protect from slugs, which love young zinnias.
6. Pinch at 20 cm When the plants reach about 20 cm with three or four pairs of leaves, snip out the growing tip just above a leaf pair. One stem becomes three or four, and the cutting stems are longer and more numerous.

Growing on: sun, water and powdery mildew

Once established, zinnias are tough. They want the sunniest spot in the garden and only need watering in long dry spells — but when you water, water the soil, not the leaves, and do it in the morning. Tall varieties in exposed gardens benefit from a few canes and string or a layer of netting; our guide to plant supports shows the options. A potash-rich liquid feed every two weeks from the first buds keeps them flowering into autumn.

The one problem almost every zinnia grower meets is powdery mildew: a grey-white dusting on the lower leaves from late August, when days are warm and nights damp. It rarely stops flowering, but it looks tired. Prevention is about air: proper spacing, no overhead watering, and removing the worst leaves as they appear. Our page on common plant diseases covers it in more detail. Zinnia angustifolia and Z. haageana are far more resistant than the big elegans types, which is a good reason to grow a few in borders and pots.

Classic zinnias or the narrow-leaved kinds?

Cutting zinnias for the vase

Zinnias do not open further once cut, so wait until the flower is fully open — then check the stem with the "wiggle test": hold the stem about 20 cm below the flower and shake it gently. If the head flops, it is not ready; if it stays stiff and upright, cut. Cut deep, just above a leaf pair low on the plant, because the side shoots that follow will be as long as the stem you leave. Strip the lower leaves and put them in clean, cool water; change the water every couple of days and expect a week or more in the vase. Regular cutting is what keeps the plants flowering: any flower left to fade tells the plant its job is done. For a full cutting garden plan, see starting a cut flower garden from seed.

Zinnias are also excellent for wildlife. Butterflies and bees visit the single and semi-double forms most, because they can reach the small true flowers in the centre — choose open-centred varieties for a pollinator garden.

Common mistakes

• Sowing too early — March seedlings outgrow their pots before it is warm enough outside. Late April is soon enough.
• Planting out into cold soil — wait until early June, or until nights stay above 10 °C.
• Pricking out from seed trays — zinnias hate root disturbance. Sow in cells or direct.
• Watering the leaves — wet foliage and crowded plants are the recipe for powdery mildew.
• Cutting too soon — a stem that wobbles will droop in the vase. Do the wiggle test.
• Not cutting at all — dead flowers left on the plant slow new buds. Cut or deadhead weekly.

Frequently asked questions

Are zinnias easy to grow from seed?
Yes — they are one of the easiest and fastest annuals there are, as long as you wait for warmth. The seed is large, germinates in under a week at 21 °C and flowers within ten weeks.

Can I sow zinnia seeds directly in the ground?
Yes, from late May once the soil is warm. Sow 5 mm deep in short rows or small groups and thin to 20–25 cm. Direct-sown plants flower a couple of weeks later than ones raised indoors, but are often sturdier.

Do zinnias come back every year?
No. Zinnias are tender annuals and die with the first frost. You can, however, collect seed from your best open-pollinated plants before then — our guide to saving zinnia, cosmos and marigold seeds shows how.

Should I pinch out zinnias?
For cutting, yes: pinch once at about 20 cm for more and longer stems. For a single big flower on a dwarf bedding plant, you can leave them unpinched.

Warm soil, full sun and a pair of scissors are all zinnias ask for in return for buckets of colour from July to October. If you are new to sowing flowers, start with our beginner's guide to growing flowers from seed. Browse the Zinnia elegans, Zinnia haageana and Zinnia angustifolia collections, everything to sow in April, the wider cut flower seeds and annual flowers, or all our seeds, and keep our growing guides to hand for the season ahead.