Growing Sunflower

The sunflower belongs to the daisy family (Asteraceae) and originally comes from the vast prairies of North America, where indigenous peoples cultivated it thousands of years ago. It arrived in Europe in the 16th century, initially as an ornamental plant. Today it's one of the world's most important oil crops, and its seeds are packed with valuable nutrients like vitamin E, plant protein and unsaturated fatty acids.

In the garden, the sunflower reliably attracts bees, bumblebees and hoverflies, loosens compacted soil layers with its strong taproot (which easily reaches over two metres deep), and can even serve as a living support for climbing plants. Young sunflowers actually turn their heads to follow the sun throughout the day, from east to west. Once the flower has fully opened, the head stays permanently facing east.

The genus Helianthus includes 67 species, but the annual Helianthus annuus is by far the most common in gardens. Depending on the variety, the range spans from compact 30 cm pot plants to true giants over four metres tall.

In the companion planting garden, the sunflower fills several roles at once: it acts as a windbreak for more delicate crops, attracts pollinators, improves the soil, and in autumn the seeds provide food for wild birds. It does have a lesser-known side, though: its roots release allelopathic substances that can inhibit the growth of certain neighbouring plants. That makes choosing the right partners all the more important.

You can get sunflowers into the bed in two ways. For starting indoors, push individual seeds about 1 to 2 cm deep into pots of compost from March or early April. At 18 to 22 °C, seedlings appear after roughly 8 to 14 days. Keep the young plants in a bright spot, but not too warm (around 15 to 18 °C), otherwise they'll shoot up and become unstable. From mid-May, once there's no more risk of frost, they can go outdoors after a hardening-off period.

Direct sowing into the bed works from late April, as soon as the soil is at least 8 to 10 °C. Push the seeds 2 to 3 cm deep, ideally several per spot, and thin out to the strongest plant later. In mild areas, you can sometimes start as early as late March. But be careful — late frosts make short work of seedlings. If you want to extend the flowering season, simply sow another batch every two to three weeks.

Protect freshly sown spots with fleece or netting, as birds, slugs and mice are equally fond of the nutritious seeds. Spacing depends on the variety: 30 to 50 cm within the row and 50 to 75 cm between rows.

Sunflowers need full sun, at least six hours a day. They'll still flower in partial shade, but noticeably more reluctantly and with less vigour. The tall varieties in particular benefit from a sheltered spot, for example in front of a wall or fence, as they snap easily in strong winds.

The ideal soil is deep, humus-rich and well-drained. Sandy loam to loamy clay is perfect. Sunflowers can't tolerate waterlogging — young plants are especially sensitive. Before sowing, loosen the soil to a depth of 30 to 40 cm and work in mature compost, as the powerful taproot needs a clear path downwards.

The variety range for sunflowers is impressive. Among the giants of two metres and above, you'll find varieties like 'American Giant' (up to five metres, golden yellow, very robust) or 'Mammut', which impress with enormous flower heads up to 40 cm across and work well as living climbing supports.

In the mid-range between one and two metres, there are varieties like 'Velvet Queen' with dark red to burgundy blooms, or 'Autumn Beauty', which produces flowers in various shades of yellow, orange and brown all at once. Pollen-free varieties like 'Sunrich Orange' are ideal as cut flowers and for allergy sufferers.

For balconies and containers, compact varieties like 'Teddybär' (40 to 70 cm, densely doubled flowers), 'Sunspot' (40 to 60 cm, but with a surprisingly large bloom) or 'Pacino' (just 30 to 50 cm) are available. These dwarfs bring joy even in the smallest spaces.

Consistent moisture is essential, especially for young plants and from bud formation through to the end of flowering. In high summer, this can easily mean watering twice a day. Waterlogging is off limits, though. In pots, pour away any excess water after 30 minutes.

When it comes to feeding: potassium matters more than nitrogen. Too much nitrogen promotes lush foliage at the expense of flowers and makes the plant prone to disease. In the open ground, well-rotted compost before sowing is usually quite enough. In pots, feed every one to two weeks with a balanced liquid fertiliser.

Tall-growing varieties appreciate a support stake — best put in early to avoid damaging the roots. Regular hoeing keeps weeds in check while the plants are still small, and a layer of mulch reduces watering effort. With branching, multi-flowered varieties, removing spent heads noticeably extends the flowering period.

The most dangerous disease is white mould (Sclerotinia sclerotiorum). You'll spot it by pale brown to whitish discolouration at the base of the stem and rotting flower heads with white fungal growth. Inside affected stems, black resting bodies (sclerotia) form and survive in the soil for years. Remove infected plant parts immediately and don't put them on the compost heap. The most important prevention is a wide crop rotation of at least four years.

Grey mould (Botrytis cinerea) appears mainly in wet weather as a grey coating on the back of the flower head. Sufficient spacing and moderate nitrogen feeding help most here. Downy mildew (Plasmopara halstedii) mainly affects young plants, causing yellow patches on the leaves with a white coating on the undersides.

Among pests, slugs are the biggest threat during the seedling stage. Birds and mice can strike both at germination and when seeds are ripening. A protective net helps in both cases. Aphids appear occasionally but rarely become a serious problem if you encourage beneficial insects like ladybirds and hoverflies in the garden.