Sunflower Seeds

Sunflower (Helianthus annuus) is the showpiece of a long, hot summer: bold golden heads on strong upright stems that follow the daylight and flower from mid-summer into autumn. It is the easy, generous choice for a sunny corner that you want full of colour and movement, and the same heads that brighten a vase will later ripen into seeds you can harvest at home. With a fast 7-to-10-day germination and a roughly 85-to-95-day run to maturity, it is one of the most satisfying flowers to grow straight from seed.

Planting

Sow directly outdoors only once all danger of frost has passed and the soil has warmed to above about 10 C, as this warm-season annual will not germinate well in cold ground. Set the seeds about 2.5 cm deep; you can stay nearer 1-2 cm for smaller varieties and go up to about 2.5-5 cm for larger seeds in light soil. Germination is fastest with a soil temperature of roughly 21-24 C, and seedlings usually break the surface within 7 to 10 days. Space plants by their final size: about 15 cm apart for small to medium types up to around 1.5 m tall, at least 30 cm for tall varieties, about 60 cm for giants, and around 45-60 cm for branching cultivars, with rows about 60-90 cm apart. Sunflowers resent root disturbance, so if you start them indoors use biodegradable pots, transplant carefully, remove any part of the pot sitting above the soil line, and harden plants off before they go out.

Fertilizing

Grow in moderately fertile, humus-rich soil enriched with organic matter such as composted manure, aiming for well-drained ground at roughly pH 6.0-7.5. Once the plants have several true leaves, after the second set of leaves appears, apply a slow-release all-purpose fertilizer. Feed only sparingly: too much nitrogen drives overly vigorous growth, distorted flower shapes and weak stems that snap. For a larger planting, split the nitrogen into two doses, half at planting and half later. Container or purely ornamental plants flower well on a potassium-rich, high-potash tomato-type feed applied as directed on the pack.

Care

Give sunflowers full sun, ideally a spot with at least 6 to 8 hours of direct light a day, since they bloom best through a long, hot summer. Water regularly and generously during early growth and around flowering, allowing roughly 2.5 cm of water per week; tall types in particular must never dry out, while pots may need watering every day in hot weather. Once plants are established, water deeply but less often to encourage deep rooting. Tall varieties benefit from staking or support against wind. Watch for birds and deer feeding on seeds and plants, plus aphids, stink bugs, leaf-footed bugs and caterpillars, and protect young seedlings, which are very vulnerable to slugs and snails. Disease problems are relatively few, though fungal issues such as Alternaria and Phoma leaf spot, rust, white mould, Rhizopus head rot, and downy and powdery mildew can appear. To harvest seeds, wait until the back of the flower head turns from green to yellow and then brown and the back petals drop, which signals the seeds are mature and ready.