Growing · sowing calendar
Sunflower sowing calendar
Month by month for Northern Europe: the Netherlands, Belgium, northern Germany, Denmark and the UK (hardiness zone 8a–8b).
Short: start seed indoors in April, direct-sow safely outdoors from mid-May (after the last frost), enjoy bloom in August–September, and harvest seed in September–October. Dates shift a week or two with the weather and with how far north you are.
This calendar covers the temperate maritime climate of north-west Europe, roughly hardiness zone 8a–8b. The pivot of the whole year is the last frost. KNMI places it, in an average Dutch spring, around mid-May, near the period called the "Ice Saints" (11–15 May). For the UK, the Met Office reports that the last frost varies by region: early-to-mid May in the south and lowlands, later in the north and at altitude. Only after that is outdoor sowing safe.
The chart above is summarised in the table below, so the information reads without relying on colour.
| Activity | Months |
|---|---|
| Sow indoors | April |
| Sow outdoors | Mid-May – June |
| Grow (vegetative) | May – August |
| Bloom | August – September |
| Harvest seed | September – October |
April: start indoors
For a head start, sow indoors or in a cold greenhouse in April. Use deep pots or root-trainers, because a sunflower's taproot dislikes disturbance. Outdoor sowing in April is pointless: the soil is too cold and a late frost is fatal. For the trade-off between starting indoors and direct sowing, see direct sow vs transplant.
May: sow outdoors after the last frost
From mid-May, once the frost risk has passed and the soil is above 10 °C (50 °F), you can safely direct-sow outdoors and plant out seedlings. For most gardeners this is the real starting gun. Sow 2–3 cm (about 1 in) deep at the spacing that suits your cultivar; the table for that is in the growing guide.
June–July: growing
Plants shoot up. Stake tall types in good time and watch for slugs on young plants — see slugs. Water deeply and infrequently; quantities are in watering and feeding.
August–September: bloom
From an April–May sowing, most cultivars bloom here from late July or August into September. Branching cultivars keep flowering for weeks. A cool spring pushes this back a week or two, as data from Wageningen University & Research (WUR) on the influence of temperature confirm.
September–October: harvest seed
When the back of the head turns yellow-brown, the seed is ripe. Harvest and dry the heads carefully; the method is at drying seeds. If you grow in pots, the same sowing-and-harvest rhythm appears in growing sunflowers in containers.
Sources
- KNMI (2024). Last spring frost date and the "Ice Saints" period (11–15 May). Royal Netherlands Meteorological Institute.
- Met Office (2024). UK last-frost dates by region. United Kingdom national weather service.
- Wageningen University & Research (WUR) (2023). The influence of temperature on the growth and bloom timing of Helianthus annuus.