When to plant sunflower seeds to ensure big and beautiful summer blooms

As a beloved staple for summer gardens, typically in full bloom from August to September, now is the time to contemplate when to plant sunflower seeds to ensure they thrive and arrive on time.

Generally speaking, April is the month to start sowing these late summer flowers; however, with the changeable weather – one minute it feels frosty, the next it is record-high seasonal temperatures – it may feel like the 'normal' planting schedule of when and what to plant in April is slightly skewed.

We've asked our team of professional gardeners to reassure us of the 'ideal' planting schedule so we can start sowing sunflowers and wait for these statuesque, mighty flowers to welcome an uplifting touch of sunshine yellow to outdoor spaces.

When to plant sunflower seeds for optimum blooms

Now is the time to start planting sunflower seeds, but the 'ideal' time depends on weather conditions and where you're planting them.

“The best time to plant sunflower seeds in the UK is April to May (but only) once the risk of frost has passed and the soil has warmed up," says Christopher O'Donoghue, co-director at Gardens Revived. "You can start them indoors in pots in early April and then transplant them outside in May.”

The timeframe of planting sunflower seeds between mid-April and late May is to ensure the ground is warm enough for the seeds to take root, like when planting spring bulbs.

Professional gardener Jane Dobbs explains why. "Germination requires a consistent temperature above 10°C," she explains. "If you plant too early, the soil might be too cold and the seeds won't germinate. In the same way, late sowing might not give the plant enough time to bloom before autumn."

Christopher O'Donoghue

A gardener with almost two decades of experience under his belt, Christopher set up Gardens Revived with his brother, Andrew, in 2018 to create a thriving family business. Together, they have worked on residential gardens, listed buildings and gardens, flower shows and large estates with some exceeding 70 acres, many with historical significance.

Jane Dobbs

Gardening is Jane's passion, having built and maintained stunning outdoor spaces for over a decade. Taking care of all the garden projects at Allans' Gardeners is her responsibility as lead gardener. A wide range of horticultural practices come into play in Jane's work, from landscape design to plant and lawn care.

To plant sunflower seeds in pots to start the seedlings off indoors, gardening expert Sarah Raven has shared her top tips. “Aim to sow sunflower seeds into 9cm pots during April and May."

“Use a potting mixture with good quality, multi-purpose, peat-free compost," Sarah advises. "Mix with a little horticultural grit to ensure good drainage.

Fill a clean pot with the potting mix and sow one seed per pot, at a depth of around half an inch. Tap in to settle the soil. Water well and leave somewhere bright but sheltered during the day."

“Once the roots have filled the pot, the seedlings reach about 30cm, and the soil is dry outside, the sunflowers are ready to go into the garden. Plant them out deep in the ground, adding a good barrow load of manure to the soil.

"They will need plenty of elbow room, so allow at least 45cm between plants. Don’t pinch them out, start tying them into a support as soon as you can, and watch them grow.”

Sarah Raven

Since the publication of her first book, The Cutting Garden (at Amazon), Sarah has led the way in introducing a new kind of productive gardening. She aims to create intense colour and beauty, combined with a practical and easy-to-achieve approach. Her popular gardening podcast Grow, Cook, Eat, Arrange has achieved 4.1 million downloads. She’s published 15 books and runs Sarahraven.com.

What is the latest date to plant sunflowers?

“The latest you can plant sunflowers in the UK is typically early July – they’re true summer blooms," says Chris. "Any time after this point, and they probably won’t have enough time to fully mature and flower before the autumn chill sets in.”

Do sunflowers grow better in pots or the ground?

As with most alluring plants, growing in the ground is better because roots are not restricted in the same way they would be in a pot. However, that said, seeds do still grow incredibly well in pots – but even the best patio container plants won't grow as big as those planted in the ground.

“Sunflowers generally grow better in the ground because they develop deep roots and can grow very tall, especially the larger varieties," Chris explains. "However, dwarf varieties (like ‘Teddy Bear’ or ‘Little Leo’) can do well in large pots – just make sure the pots are deep and have good drainage.“

Jane offers her advice to guarantee planting success from a pot: "Ensure the container is big enough, ideally at least 30cm wide and deep. Put pots in full sun for at least 6 hours a day.

"It's also more important to water and feed potted plants regularly since soil nutrients deplete faster," Jane helpfully points out, for watering your garden plants accordingly.

Growing them in pots doesn't apply to seedlings in smaller pots if you are growing them indoors first. These will then be transferred to the ground in the garden where they can thrive.

Do I have to soak sunflower seeds before planting?

Many people recommend soaking sunflower seeds before planting to speed up the germination process, but you don’t have to do it – they will still germinate easily on their own.

If you do choose to soak them, follow Jane's helpful advice to get it right. "If you want to soak seeds, put them in lukewarm water for 8-12 hours the night before sowing," she says. "Sprouting is easier when the seed coat is softened.

But she does warn: "Don't soak them longer than 24 hours, or they'll rot."

Sunflower seed planting tips

Know we know when and where is best to plant sunflower seeds it felt only right to ask the gardening professionals for their top tips on the actual planting process.

Here are Jane's sunflower seed planting tips:

• Make sure your soil is well-drained, loose, and enriched with compost.
• Do not use heavy clay without amending it with organic matter.
• Directly plant sunflower seeds 1.5 to 2.5 cm deep. If you have smaller varieties, space them 30cm apart, and taller varieties 45-60cm apart to ensure airflow.
• While germination is occurring (7-10 days), keep the soil moist but not soggy. Sunflowers tolerate drought once they're established.
• You should stake tall sunflowers over 1.5 meters to prevent damage from heavy rain and winds (although here's hoping for none of that this summer).

After enjoying your sunflowers all summer long, it pays to carry out essential plant propagation by mastering how to harvest sunflower seeds to ensure you can grow another bumper crop next summer. Saving the seeds to plant next year is a great way to fill beds and borders with an uplifting touch of sunshine yellow at zero cost.