Sunflowers are the most satisfying flower a beginner can grow: they germinate fast, grow visibly taller almost every day, and end the summer as giant golden heads that tower over the garden. Children love them, bees love them, and a row of sunflowers along a fence is the simplest way to make a garden feel like summer.
The trick with sunflowers is that they do exactly what their name suggests — they need full sun and plenty of it, and they grow fast enough to need support in windy spots. Dwarf varieties suit pots and small gardens, while the giant types can reach three metres or more, so check the variety before you sow and give the tall ones a sheltered spot and a stake.
Sunflowers at a glance
| Growing factor | What sunflowers need |
|---|---|
| Sun | full sun |
| Soil pH | 6.0–7.5 |
| Days to germination | 7–14 |
| Days to maturity | 70–90 |
| Spacing | 18–24 inches apart |
| Water needs | moderate |
| Cold tolerance | tender |
| Family | Asteraceae |
Starting seeds
Sunflowers are direct-sown where they are to grow — they dislike transplanting, so skip the seed trays. Sow after the last frost, when the soil has warmed: in Zones 3–5 that is late spring, in Zones 6–8 mid-spring, and in Zones 9–10 early spring, with a second sowing possible in late summer. Zones 11–13 are frost-free, so you can sow in succession through much of the year; check your local extension service for the best local sowing dates. Seeds germinate in 7–14 days in warm, moist soil. Sow at the spacing in the at-a-glance table above rather than thickly and then thinning hard — although thinning is still needed if germination is patchy, sow thinly to start. Cover lightly, keep the soil evenly moist until seedlings appear, and mark the row so you do not weed out the seedlings by mistake. Our seed starting calculator and germination time calculator help you plan sowing dates, and the seed spacing calculator works out row spacing.
Transplanting and planting out
Sunflowers are sown where they grow, so there is no transplanting step — instead, thin the seedlings once they are a few inches tall, leaving the strongest one at each 18–24-inch spacing. Thin on a damp day, water the row first so the remaining seedlings are not disturbed, and snip out the extras rather than pulling them, which can damage the roots of the ones you keep. Our plant spacing calculator works out exactly how many plants fit your bed, and the square foot garden planner helps lay them out.
Soil and feeding
Sunflowers grow best in fertile, well-drained soil with a pH of 6.0–7.5. Dig in compost before planting — it feeds the soil and helps it hold moisture without getting soggy — and mulch after planting to keep the roots cool and the weeds down. Feed during the growing season with a balanced fertiliser at the label rate, roughly once a month while plants are actively growing, and stop feeding as the season ends. Our fertiliser calculator works out the right amount for your bed, and the compost ratio calculator helps you make good compost to dig in.
Watering
Sunflowers have moderate water needs: keep the soil evenly moist while plants are establishing and flowering, and water deeply rather than little and often so the roots grow down. Water at the base in the morning so the foliage dries during the day, mulch to hold moisture in, and watch for wilting in hot, dry spells. Our watering calculator gives a starting point for your bed size, and the watering schedule generator can build a routine around it.
Sunlight and temperature
Sunflowers need full sun — at least six hours of direct sun a day. Sunflowers are tender — frost kills them or damages them badly, so they are grown as warm-season plants in most zones and planted out only once frosts are over. In frost-free Zones 11–13 they can grow for much of the year. Use the frost date calculator to find your last frost date. Our sunlight calculator can check whether your spot gets enough sun.
Pests and diseases
The pests and diseases to watch for on sunflowers are aphids, slugs, thrips. Aphids cluster on the stems and under the leaves, and slugs can eat young seedlings. Birds are the biggest threat to ripening seed heads, so cover heads with netting or an old stocking if you want the seed for yourself. Check plants weekly, looking under leaves as well as on top, and act early. Hand-pick larger pests, knock aphids off with a strong spray of water, and remove badly affected leaves. Keep the area weed-free and avoid wetting the foliage when you water, since damp leaves invite fungal disease. Our pest identifier helper can help identify what you are seeing, and the plant disease checker helps narrow down leaf and stem problems.
Companion plants
Good companions for sunflowers are lavender, marigolds, garlic, chives. Lavender, marigolds, garlic and chives are good neighbours: marigolds help with soil pests, and lavender draws in the pollinators that sunflowers depend on. Our companion planting finder can suggest more pairings for your bed plan.
Harvesting
For cut flowers, pick sunflowers when the petals are just opening and the head is still firm — they last a week or more in water. For seed, wait until the back of the head turns yellow-brown and the seeds are plump and striped, then cut the head and hang it upside down in a dry, airy place to finish drying. Rub the seeds out once dry, and store them in a jar. Leave a few heads on the plants for the birds over winter. Our harvest date calculator can estimate your picking date from your sowing date, and the vegetable yield estimator helps you work out how much a bed will produce.
Common problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Plants fall over | wind and shallow roots | Stake tall varieties early, and plant in a sheltered spot. |
| Heads droop and stems bend | heavy heads after rain | Support the stem and shake rain off the heads after storms. |
| Seedlings disappear | slugs or birds | Protect seedlings and sow a few extra to allow for losses. |
Plants fall over
A tall sunflower in flower is top-heavy, and one windy night can flatten a whole row. Stake plants when they are about knee-high, before they need it, and tie them loosely as they grow. Planting against a fence or wall gives shelter as well as support.
Heads droop and stems bend
A sunflower head full of rain is heavy, and the stem bends under the weight. This is usually harmless — the head often straightens as it dries — but a stake prevents the stem snapping in a storm.
Seedlings disappear
Birds pull up young sunflower seedlings and slugs eat them at night, so sow a few more than you need. A cloche or a cut-off bottle over each seedling protects it until it is big enough to be left alone.
Frequently asked questions
How long does it take to grow sunflowers?
From planting to maturity takes 70–90 days. Seed germination takes 7–14 days, and the total time depends on whether you start from seed, a nursery plant, or a bulb or cutting.
How far apart should I plant sunflowers?
Space sunflowers 18–24 inches apart. That spacing gives each plant room for air movement, which keeps disease down, and room to reach its full size without crowding its neighbours.
What soil pH do sunflowers need?
Sunflowers prefer a soil pH of 6.0–7.5. Test your soil before amending it — most garden soils are close enough, and guessing with lime or sulphur can do more harm than good.
How tall do sunflowers grow?
It depends on the variety: dwarf types stay under 60 cm, while giant types can reach three metres or more. The spacing in this guide, 18–24 inches apart, suits the tall garden varieties.
Do sunflowers need a lot of water?
They have moderate water needs, but they drink heavily while growing fast in summer. Water deeply at the base, especially in dry spells, and mulch to hold moisture in the soil.