How to Grow Sunflowers: A Step by Step Guide

If you want to put a smile on your face this year, grow sunflowers.

You’ve probably already had a go: growing giant sunflowers is a rite of passage when you’re a kid. My daughter - now 21 – still has the certificate she was presented with at the age of six, after growing a neck-cricking 3.6m (12ft) sunflower in our back garden for a local competition. Even that triumph was dwarfed, however, by the world record beater: grown in Germany in 2014, it topped out at 9.17m (30ft 1in). That’s taller than my house.

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But it’s not all about impressing the neighbours, winning certificates, or even pretty flowers. Sunflowers are a crop in my garden, earning their keep with their generous harvest of protein-rich, oil-rich seeds.

About one dessertspoonful of sunflower seeds provides over a third of your daily dose of vitamin E, essential for healthy skin and eyes. I scatter them raw over my morning muesli, bake them into bread, or sprinkle them into salads and roasted vegetables. Occasionally I’ll sprout some on the windowsill for winter microgreens.

Now is just the right time to get sowing, so read on for my foolproof guide to how to plant sunflower seeds, so you too can put a little more sunshine into your life.

Which sunflower seeds to plant

For the biggest harvests grow whoppers like ‘Giraffe’ or ‘Titan’, each massive flower head holding up to 2000 seeds. Multi-headed varieties are easier to accommodate as they’re shorter, with smaller but plentiful flowers. Red-brown ‘Velvet Queen’ grows 1.8m (6ft) tall, while ‘Little Dorritt’, at just 60cm (2ft) tall, fits into roomy containers

When to plant sunflower seeds

Sunflowers can’t handle frost, so wait until at least mid-April (southern UK) or, better, mid-May to sow outside. Or start seeds under cover from early March: once the weather warms up they’ll be sturdy youngsters with a good head start on the season.

How to plant a sunflower seed:

Sunflower seeds are germinate quickly, usually within 10 days. You can sow them two ways:

Sowing into pots

Fill 8cm (3”) pots with peat-free multipurpose compost. Make a hole about 2cm (1”) deep, and drop in a single sunflower seed. Cover with more compost, then pop into a heated propagator or onto a bright windowsill to germinate.

Keep sunflower seedlings warm and well watered, and repot into the next size larger pot each month. They’re ready to go out once they’re 30cm (1ft) tall and the weather outside is warm, usually early June.

Sowing into the ground

Sunflowers sown outside often grow into sturdier plants, but they’re more vulnerable to pests. Choose your sunniest spot, and water first if it’s dry. Make a hole about 2cm (1”) deep, drop two sunflower seeds in and cover with more soil.

Pop a home-made bottle cloche over the top, made by cutting the bottom off a two-litre plastic drink bottle and removing the lid. Sink it firmly into the ground to keep out slugs. If both seeds germinate, remove the weakest. Remove the cloche once the plant touches it.

Supporting your plant

For tall varieties, hammer a 1.5m tree stake firmly into the ground alongside each plant – it’ll look ridiculous at first but you’ll be glad you did! Don’t be tempted to use canes as they’ll topple under the weight of a fully-grown sunflower.

Feeding and watering

Before planting, spread a barrowload of well-rotted manure or home-made garden compost per square metre over the soil. Feed young plants weekly with growth-boosting liquid seaweed or nettle feed, then once flowers form switch to potassium-rich comfrey feed or tomato feed to encourage big, beautiful blooms.

When do sunflowers bloom?

Sunflowers bloom about four months after sowing – so seeds sown in March flower in July. Lengthen your sunflower season by sowing a few each month from March till May, for flowers from July to September.

How to harvest sunflower seeds

Once you (and your local bees) have enjoyed the flowers to the full, the petals wither as seeds form.

Seed-packed sunflower heads are hugely popular with garden birds, so leave a head for them, but harvest the rest once about two thirds of the seeds are stripy black-and-white. Cut the head and hang it indoors somewhere dry and cool to finish ripening for a fortnight.

Then hold the head over a tray and rub the seeds free. Set aside a few to sow next spring, and store the rest in a jar. Shell the seeds as you need them to enjoy through winter.