Annual
How to grow zinnias
Zinnia elegans
Zinnias are half-hardy annuals that need warmth more than anything else. Sow one seed per module indoors in mid to late April, or sow direct into warm soil from late May to mid June, and plant in the sunniest, most sheltered spot you have, 30 cm apart. They flower from July to October. Two things undo them: cold, which stops growth dead, and root disturbance, so never prick them out or plant them into chilly ground.
- Hardiness
- Half-hardy annual, dislikes root disturbance
- Position
- Full sun, warm
- Soil
- Fertile, free-draining
- Ideal pH
- 6.0 to 7.5
- Water
- Moderate, at the base, not on the leaves
- Feeding
- Moderate feeder
Sowing and planting zinnias
WhenSow Apr indoors in modules or late May to Jun direct; flowers Jul to Oct
Starting off
Sow Apr indoors at 21 to 24 °C, one seed per module, 1 cm deep, and keep warm as it germinates in 5 to 7 days; plant out after the last frost in late May without disturbing the roots. A direct sowing in late May to Jun into warm soil is often stronger.
Spacing and planting
Tall varieties 30 cm apart, dwarf 20 cm; sow 1 cm deep. Dwarf types are fine in a 25 cm pot in full sun.
Varieties worth growing
- 'Benary's Giant' series
- The cut-flower standard: large double flowers on strong 1 m stems, in single colours or a mix, with some tolerance of mildew.
- 'Queen Red Lime'
- Dusky rose petals shading to lime at the centre; the fashionable one for arranging, 75 cm.
- 'Envy'
- Chartreuse green double flowers, 60 cm; a foil for brighter colours and it takes a little light shade.
- 'Oklahoma' series
- Smaller double and semi-double flowers on branching 80 cm plants; very productive and less prone to mildew.
- 'Profusion' series
- Compact 30 cm mounds of single flowers that need no deadheading and shrug off rain and mildew; the one for pots.
Zinnias month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Nothing to do.
- February
Nothing to do. Order seed.
- March
Nothing to do. It is too early to sow.
- April
Sow indoors from the middle of the month, one seed per module, at 21 to 24 °C.
- May
Harden off slowly. Plant out in the last week once nights are mild, or sow direct into warm soil.
- June
Sow direct until the middle of the month. Pinch out the tip at 20 cm.
- July
First flowers. Cut stems hard, to just above a pair of leaves.
- August
Keep cutting and deadheading. Feed. Water at the base in dry weather.
- September
Flowering continues. Save seed from the best open-pollinated plants.
- October
Pull plants after the first frost.
- November
Nothing to do.
- December
Nothing to do.
Feeding zinnias
A moderate feeder that wants phosphorus and potash rather than nitrogen. A base dressing at planting, then a flower feed once buds show. Do not feed in a cold spell: the roots cannot use it.
Moderate, a balanced-to-potassium feed supports the bright blooms.
Feeding plan
Planting or direct sowing, beds
100 g/m², the low end of the label range of 100 to 300 g/m², raked into the top few centimetres: roughly three handfuls per square metre.
From first buds, beds, every four to six weeks
100 g/m² scattered between the plants and watered in. Two applications, in July and August, are usually enough.
From first flowers, pots, every two weeks
3 g per litre of compost, the low end of the label: about 20 g on the surface of a 25 cm pot holding 7 litres, watered in.
From planting out to September, every two to three weeks
1 g per litre of water, the label rate, poured round the base rather than sprayed on the leaves: 10 g in a 10 litre can.
Signs to watch
Leaves yellow between the veins and growth sluggish in a cold May
Roots too cold to take up nutrients
Wait for warmth; do not feed
Lush foliage and few flowers
Nitrogen excess
High-potash feed only
Stunted plants with purple undersides
Phosphorus locked up in cold soil
Warm the ground with fleece
Pests, diseases and problems
Seedlings and young plants eaten to the ground overnight
Slugs and snails, which seek out zinnias
Plant out sturdy plants with five or six leaves, check every evening for the first two weeks, and apply nematodes to moist soil in May. Direct sowings need the same watch.
Seedlings stop growing, turn pale or collapse at the base
Cold check or damping off, from sowing too early or overwatering in low temperatures
Do not sow before mid April, keep seedlings above 15 °C, water sparingly from below, and never plant out until nights are reliably mild.
White powdery coating on leaves from August
Powdery mildew, encouraged by dry roots and cool, damp nights
Water at the base in the morning, give plants their full spacing, pick off the worst leaves, and grow 'Oklahoma' or 'Profusion' where it is a regular problem.
Red-brown spots with grey centres on leaves, sometimes spotting on petals
Alternaria leaf spot, spread by water splash and carried on seed
Keep water off the leaves, remove spotted foliage, and do not save seed from affected plants.
Petals ragged and chewed, flowers lopsided
Earwigs feeding at night
Trap them in upturned pots stuffed with straw on canes among the plants and empty the pots each morning.
Stems brown and rot, with grey fluffy mould, in a cool wet spell
Grey mould
Cut out affected stems to healthy tissue, clear spent flowers, and thin plants to improve air movement.
Pruning
Pruning and care
Pinch the tip at 20 cm tall for more branching stems. Deadhead or cut flowers hard to a leaf pair, as cut stems grow back with more buds. Tall types need a ring of canes or twigs in an exposed plot; an annual, so pull after the first frost.
Good to knowLoves heat; sow direct after frost. A great cut flower, picking makes more.
Growing zinnias in pots
Compact zinnias such as 'Profusion' do well in a 25 cm pot, about 7 litres, with three plants in peat-free multipurpose compost. Sow directly into the pot in late May, or plant module-raised plants without breaking the root ball. Put the pot in the hottest, sunniest place available, against a south-facing wall if you can. Water at the base in the morning and let the surface dry between waterings; zinnias dislike wet leaves and soggy compost. Tall cut-flower varieties need a 40 cm tub and a cane each, and are better in the ground.
Zinnias: common questions
When should I sow zinnia seeds in the UK?
Sow zinnias indoors from mid to late April, or directly outdoors from late May to mid June. They germinate in under a week in warmth and grow fast, so nothing is gained by starting earlier; seedlings held back in cool conditions stall. Use modules, one seed in each, so the roots are not disturbed at planting.
Should I pinch out zinnias?
Yes, pinch out the growing tip when the plant is about 20 cm tall, just above a pair of leaves. This gives a bushier plant with many more flowering stems, and longer stems for cutting. Each time you cut a flower, cut low, to just above a leaf pair, and the plant branches again.
Why are my zinnias not growing?
Cold is the most common reason. Zinnias stop growing below about 10 °C and sulk for weeks after a chilly spell, cold wind or planting into cold soil. Disturbed roots have the same effect. Wait until late May, plant into a warm, sheltered bed in full sun without breaking the root ball, and do not feed until growth picks up.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.