When to Plant Sunflowers (UK Guide)

Knowing when to plant sunflowers is key to growing strong plants with large, healthy flowers. Sunflowers are warm-season plants, so timing matters—plant too early and they can fail, plant at the right time and they thrive.

⭐ Recommended Products — Sunflowers & Sunflower Seeds

Sunflowers are bright, cheerful plants that are easy to grow from seed and great for gardens, borders, or kids’ projects.

• Sunflower Seed Collection (Multiple Varieties)
Includes popular types like classic tall giants, dwarf/multi-head varieties, and colourful mixes — great for diverse planting.
👉 Click here to see top options

• Sunflower Seed Starter Kit (Trays + Labels + Compost)
A complete beginner-friendly kit with everything you need to sow sunflower seeds indoors or in a cold frame before planting out.
👉 Click here to see top options

• Sunflower Support Stakes & Twine Set
Tall varieties often need support — this kit helps keep stems upright as they grow toward the sun.
👉 Click here to see top options

• Bird & Wildlife Sunflower Seed Mix
Also great for feeding wild birds later in the season or sowing separate patches to attract wildlife into your garden.
👉 Click here to see top options

• Grow Lights / Heat Mat (Optional for Early Sowing)
Boost germination and early growth if you’re starting seeds indoors before outdoor planting is warm enough.
👉 Click here to see top options

This guide explains the best time to plant sunflowers in the UK, whether indoors or outdoors.

🌻 Best Time to Plant Sunflowers in the UK

In the UK, sunflowers are usually planted between March and May, depending on how and where you’re growing them.

Quick overview:

• March–April: sow indoors
• April–May: sow outdoors
• Late May–June: latest safe planting time

Sunflowers need warmth and light to grow well.

🌱 Planting Sunflowers Indoors

Best time: March to April

Planting sunflowers indoors gives them a head start, especially in colder areas.

Why plant indoors?

• Protects seedlings from frost
• Encourages stronger early growth
• Ideal for giant sunflower varieties

Seeds are usually sown in pots or root trainers and kept somewhere bright and frost-free.

🌞 Planting Sunflowers Outdoors

Best time: Late April to May

Sunflowers can be planted directly outdoors once:

• Frost risk has passed
• Soil has started to warm

In most parts of the UK, this is late April or May, though colder regions may need to wait until late May.

❄️ Can You Plant Sunflowers Too Early?

Yes. Planting sunflowers too early can cause problems:

• Seeds may rot in cold, wet soil
• Seedlings can be damaged by frost
• Growth may be slow or stunted

Sunflowers dislike cold conditions, so patience pays off.

🌡️ What Temperature Do Sunflowers Need?

Sunflowers grow best when:

• Soil temperatures are above 10°C
• Daytime temperatures are mild and sunny

Warm soil helps seeds germinate quickly and evenly.

🌻 Latest Time You Can Plant Sunflowers

The latest recommended planting time in the UK is early June.

Later sowings can still grow, but:

• Plants may be shorter
• Flowers may be smaller
• Blooming time may be reduced

Earlier planting usually gives the best results.

🌼 Final Thoughts

The best time to plant sunflowers in the UK is spring, once conditions begin to warm. Start seeds indoors in March or April, or sow them outdoors from late April to May for reliable results.

Getting the timing right ensures strong plants, tall stems, and spectacular summer flowers.