When to Plant Sunflowers in the UK

Sow sunflower seeds indoors from mid-April, or straight outside from late April to May. Wait until the soil has warmed up, and keep young seedlings safe from slugs and late frosts.

The RHS sunflower guide says to plant indoor-raised seedlings out only once the frosts are over. This guide covers timing around the UK, sowing indoors and out, giant and dwarf varieties, and late sowing. For staking and feeding, see how to grow sunflowers.

When to sow sunflowers indoors

Start sunflowers indoors from mid-April. That gives them a head start of a couple of weeks before they go outside after the last frost.

Indoor sowing method

Sow one seed per 9cm pot, 2cm deep, in multipurpose compost. The seeds are big and easy for little hands. They come up in 1-2 weeks on a warm windowsill.

Sunflowers shoot up fast indoors. One sown in mid-April can be 15-20cm tall in three weeks. Don’t sow before mid-April, or they’ll outgrow their pots before it’s safe to plant them out. March-sown sunflowers end up tall, leggy and pot-bound.

One seed per 9cm pot, 2cm deep. The big seeds are easy to handle.

Transplanting

Plant them out from late May in southern England and early June in the north. Sunflowers don’t like their roots disturbed, so handle the rootball gently. Fibre pots that go straight into the ground get round this nicely.

Water well after planting and put a strong stake in for tall varieties straight away. A 2m sunflower in August catches the wind like a sail, and staking early saves damaging the roots later.

Gardener’s tip: Sow a few spares in case slugs get to some. Slugs love sunflower seedlings, especially in the first fortnight after planting out. A ring of copper tape or a few wildlife-friendly slug pellets around each plant helps. See our guide on getting rid of slugs for more ideas.

Seedlings ready for planting out. At 15-20cm tall, these April sowings can go outside from late May.

When to direct sow sunflowers outdoors

Sowing straight outside is the easiest way. No potting on, no hardening off and no roots to disturb.

Outdoor sowing timeline

Sunflower seeds want the soil at about 10C. A soil thermometer pushed 5cm into the ground tells you. In colder soil, the seeds sit there and rot or come up slowly. In a warm spring, southern gardens get there by late April. In a cold one, wait until early May.

How to direct sow

Sow seeds 2cm deep, one per spot. Space dwarf types 30cm apart, standard ones 45cm and giants 60cm. If the soil is dry, water before you sow. Cover with soil and firm gently.

Pigeons and sparrows love digging up the big seeds. Cover the area with wire mesh or fleece until the seedlings are up, and take it off once they reach 10cm.

Variety comparison and timing

Different sunflowers flower at different speeds. Pick the right one for when you’re sowing and you’ll get flowers when you want them.

Giant varieties

Giant sunflowers need the longest season. Sow indoors in mid-April for the earliest start, or outside in early May in the south. In northern England and Scotland, start giants indoors, as the outdoor season may be too short.

Giants are top-heavy, so stake them once they’re 60cm tall. A 2.4m cane or a sturdy wooden stake works well. Tie the stem loosely with soft string as it grows. Never tie tightly, as the stem thickens fast.

Dwarf varieties

Dwarf sunflowers are perfect for pots, borders and children’s gardens. They flower quickly and stay under 60cm. Sow outside from late April. They’re the best choice for a late sowing, and even a June sowing flowers by August.

Sunspot and Teddy Bear are the favourites. Sunspot has one big flower on a short stem. Teddy Bear has fluffy double flowers that last well in a vase.

Dwarf sunflowers stay under 60cm, so they’re perfect for pots and children’s gardens. Even a June sowing will flower by August.

Multi-headed varieties

Multi-headed sunflowers give you lots of smaller flowers on branching stems. They’re better for cutting and flower for longer than single-headed ones. Velvet Queen, Autumn Beauty and Italian White are all multi-headed.

They’re great for wildlife too. Every flower feeds bees and other pollinators, and the seed heads bring in finches and tits through autumn and winter. For more pollinator ideas, see our guide on bee-friendly garden plants.

Good to know: Some modern sunflowers are pollen-free, bred for the cut flower trade. They’re much less use to bees. Check the packet and choose varieties with pollen if you want to help wildlife.

Growing conditions

Sun

Sunflowers need full sun, ideally a south-facing spot. Here’s a fun fact: young plants follow the sun across the sky, facing east in the morning and turning west by evening. Once the flower opens fully, it settles facing east.

Soil

Sunflowers grow in most soils but like rich soil that drains well. Their deep roots find water other flowers can’t reach. On heavy clay soil, dig in some compost before planting.

Shelter

Wind is the big enemy of tall sunflowers. A spot against a wall or fence stops stems snapping. Stake anything over 1m tall early on. In a windy garden, go for dwarf or multi-headed types, which cope better.

Water

Water regularly in dry spells, especially while they’re settling in and when the flower buds are forming. A deep soak twice a week beats a sprinkle every day. Once they’re established, sunflowers cope well with dry weather.

Sowing calendar by purpose

Saving seeds and feeding birds

Leave the old flower heads on the plant in autumn. The seeds ripen over 4-6 weeks after the petals fall. They’re ready when the back of the head turns brown and dry and the seeds feel firm.

Cut the heads and hang them in a dry shed for a week to finish drying. Keep some seeds in paper bags for next year, or hang the heads in the garden as bird feeders. Goldfinches, greenfinches and blue tits love them through winter.

Or just leave the heads on the plants. Birds will pick the seeds out themselves, and the hollow stems give insects somewhere to shelter over winter. It’s an easy way to help garden birds through the leanest months.

Common mistakes

Sowing too early indoors

Sunflowers grow so fast that March sowings are tall and pot-bound long before it’s safe to plant them out. Wait until mid-April. A few weeks indoors is all they need.

Planting in shade

In part shade, sunflowers stretch and lean towards the light, giving weak stems and small flowers. They flower late and give fewer seeds. Full sun really is a must.

Spacing too closely

Crowded sunflowers fight for light and water. You get thin stems, small flowers and more mould in damp weather. Stick to 30cm for dwarf, 45cm for standard and 60cm for giants.

Ignoring slug protection

Slugs adore sunflower seedlings and can strip one to a bare stem overnight. Protect them for the first two weeks after planting out or coming up, with copper tape, wildlife-friendly pellets or nematodes.

Not staking early enough

An unstaked 2m sunflower can snap in a summer storm. Put the stake in at planting time or when seedlings reach 30cm. Staking a big plant later can damage the roots. Tie the stem loosely every 30cm or so as it grows.

A tall sunflower tied to a cane. Stake early so you don’t damage the roots later.

Got your timings sorted? Read our full guide on how to grow sunflowers next.

Frequently asked questions

When is the best time to plant sunflower seeds UK?

Late April to early May is ideal for sowing outside. Wait until the soil has warmed to about 10C. Sowing indoors from mid-April gives you a head start of a couple of weeks. The seeds usually come up in 1-2 weeks.

Can I plant sunflower seeds in March?

It’s too early, indoors or out. Sunflowers grow so fast that March-sown seedlings get tall and leggy. They can’t go outside until late May, so they outgrow their pots long before then.

How late can I sow sunflowers in the UK?

Until about mid-June for late summer flowers. Dwarf types sown in June still flower by August. Giants sown after early June may not reach full height before autumn.

How long do sunflowers take to grow?

Roughly two to three months from sowing to flowers. Dwarf types are quickest, at around 60-70 days. Giants take longest, at around 90-100 days. A warm, sunny summer speeds things up.

Should I sow sunflowers indoors or outdoors?

Both work well. Sowing indoors gives you a head start and keeps the seedlings safe from slugs. Sowing outside is simpler, and the plants never have to be moved. They don’t like their roots disturbed, so use pots that can be planted whole if you start them indoors.