How to grow sunflowers

Demonstrated by the RHS. This guide is based on the "How to Sow Sunflowers" video produced by the Royal Horticultural Society, featuring Faye Howells at RHS Garden Bridgewater. The RHS is the UK's leading gardening charity, and the video covers the key steps from seed to established plant with practical demonstrations in a proper working garden setting.

1. Pick the right variety for your space

Sunflowers range from enormous single-headed giants like Mongolian Giant (which can reach 3 metres or more) down to compact multi-headed varieties like Sunbright Supreme that sit happily in a large pot. Think about where you're planting before you buy seed.

For a border or against a sunny fence, tall single-headed varieties look dramatic and produce big seed heads worth harvesting. For a smaller garden or a container on a patio, choose a dwarf or multi-branching type. Children particularly enjoy the giant varieties - growing one as tall as possible makes for a decent summer project.

2. Sow indoors in April or direct in May

In the UK, the best approach is to sow sunflowers indoors in April using individual deep pots - roots resent being disturbed, so avoid seed trays you'd normally prick out into. A 9 cm pot or a cardboard tube works well. Sow one seed per pot, about 1–2 cm deep.

Alternatively, sow direct into the ground from mid-May once the risk of frost has passed. Direct sowing often produces sturdier plants than those grown indoors, especially if you can protect them from slugs in the early weeks. In Sandwich and East Kent the last frost date is typically around mid-April, but May is safer.

3. Keep seedlings on a bright windowsill, not a warm dark corner

Sunflowers germinate quickly - usually within a week. Once they're up, they need as much light as possible or they go leggy fast. A south-facing windowsill is ideal. Avoid the airing cupboard method some people use to germinate seeds; once they've sprouted they need daylight immediately.

If you've started them early and they're getting tall before planting-out time, move them somewhere slightly cooler - a greenhouse or cold frame - to slow the growth down and harden them off at the same time.

4. Plant out after the last frost in a sunny sheltered spot

Sunflowers want full sun - at least six hours a day - and some shelter from strong winds. A south-facing fence or wall is ideal. Prepare the ground with a bit of general-purpose fertiliser worked in, but don't go overboard; very rich soil produces leaves at the expense of flowers.

Plant at the same depth as the pot. Space large varieties at least 45 cm apart; dwarf types can be closer. Water in well and, if there's any risk of late frost in your area, keep some fleece handy for the first couple of weeks.

5. Water deeply but not constantly

Once established, sunflowers are reasonably drought-tolerant. Water at the base, not the foliage, and let the top few centimetres of soil dry out between watering. Consistent deep watering once or twice a week in dry spells is better than a daily light sprinkling.

During the flowering period, watering matters more - a dry spell when the heads are forming can produce smaller flowers and fewer seeds. That said, standing water around the roots can cause problems too. Good drainage is the thing.

6. Stake tall varieties before they need it

Get a stake in early - a bamboo cane or a proper garden stake for large varieties - before the plant gets tall. Waiting until the sunflower is 1.5 metres and already leaning is much harder work. Tie loosely with garden twine; allow for the stem to sway a little in the wind rather than lashing it tight.

Giant varieties may need a stout post rather than a cane, especially in an exposed garden. East Kent can be quite breezy, and a 2.5 metre sunflower in full leaf is essentially a sail.

7. Leave the heads to dry for seed harvesting

If you want to save seeds - to replant next year or to feed garden birds - leave the heads on the plant until the back turns brown and the seeds feel firm. Then cut the head off, wrap it loosely in paper, and hang it upside down somewhere dry and airy for a few weeks.

Once fully dry, rub the seeds free, discard any that look hollow or damaged, and store in a labelled paper envelope somewhere cool and dry. Seeds stay viable for two or three years if stored properly. Bird feeders: just hang the whole dried head outside.

When to call a handyman

Sunflowers mostly sort themselves out, but if you're preparing a new bed, putting in raised planters, or clearing ground that's been neglected for a while, Richard can help with that groundwork. Border preparation and raised bed construction are both regular jobs around Sandwich and the villages.