When to plant sunflower seeds

Sunflowers are easiest sown straight where they are to flower, from mid-April through May. In the UK and in mild parts of Central Europe you can start in mid-April; in colder areas wait until May, when the soil has warmed a little. They sprout in cool soil, but slowly, and slow seedlings are what slugs and birds get to first.

For earlier flowers, or where slugs are bad, sow in pots indoors from late March to May. Plant them out once there is no more risk of frost, usually mid to late May in Germany, Austria and Switzerland, after hardening them off for a week.

Young sunflowers can take a touch of cold, but not a hard frost. A spring-sown plant flowers from mid to late summer; sowings in pots into June still flower, just later.

Choose the sunniest spot you have. Sunflowers grow in most soils as long as they drain, but they reward humus-rich ground: dig in compost before sowing. In shade they flower poorly.

Push the seeds about 0.8 in deep, a little deeper if birds keep digging them up, and water them in. At about 59°F they come up in one to two weeks. Sow a few more than you need, 4 in apart, then thin to the strongest plants once they are growing well.

Final spacing depends on the variety. Branching and dwarf types need about 12 in, single-stemmed giants about 18 in. In a 120 × 80 cm raised bed that means eight small sunflowers at most; giants belong along a fence or at the north side of the vegetable garden, where their shade doesn't fall on other crops.

In pots, sow one or two seeds per pot and keep the stronger seedling. Plant out before the roots circle the pot.

Sunflowers are thirsty, especially the tall ones: keep the soil evenly moist through summer, and water plants in pots daily in hot weather. Field sunflowers cope with drought, but a garden plant that dries out flowers smaller.

A rich bed with compost is usually enough. If growth is slow, a potassium-rich feed such as tomato fertiliser encourages flowering.

Put a strong cane in beside each tall variety when you plant it, rather than later when you might spear the roots, and tie the stem to it loosely as it grows. A sunflower in full head is heavy and catches a lot of wind.

For the vase, cut sunflowers in the morning and put them straight into water. Smaller, branching varieties are the best cut flowers because each plant keeps producing blooms over many weeks.

For seeds, leave the heads on the plant. They are ripe when the back of the head turns from green to yellow-brown, the petals have dried and dropped, and the head hangs down. Pull out a few seeds: they should be plump and have their typical striped or dark coat.

Birds get there first if you let them. Once the petals start to brown, tie a paper bag or a piece of fine mesh over the head. Then cut the head with a length of stem attached, hang it somewhere warm, dry and airy until the seeds loosen, and rub them out. Store fully dry seeds in a closed jar.

Or leave a few heads standing for the birds. Birds will pick them clean through autumn, or cut the heads, dry them and hang them out as winter bird food.

Single-stemmed giants such as 'American Giant' can reach 3 to 4 metres with one huge head; they are the ones for seeds and for competitions. Branching varieties stay lower and carry many smaller flowers over a long season, in yellow, bronze, red or cream. Dwarf types from about 12 in fit pots and the front of a bed.

For bees and bumblebees, choose varieties with plenty of pollen: the brown disc florets in the middle are rich in pollen and nectar.

Slugs and snails are the biggest threat, and only while the plants are young. Once the stems are woody they leave them alone. Raising plants in pots until they are sturdy is the easiest protection. Birds also dig up freshly sown seed.

In wet summers, powdery mildew coats the leaves late in the season, and Sclerotinia, a fungal rot, can take hold. Give plants room so the leaves dry quickly, and clear away diseased plants.

Sunflowers belong to the daisy family, Asteraceae, with lettuce, chicory, marigolds and calendula. Grow them in a different spot each year, as with any annual.

Sunflowers are often said to stunt their neighbours. There is something to it: research shows that sunflower roots and residues release compounds that hold back the germination and growth of some plants, and sunflowers have been studied as a way to suppress weeds. Most of that work was done in the lab or in fields, so how much it matters in a mixed garden is unclear.

In practice, a giant sunflower mostly competes through shade and thirst. Place tall ones where their shade falls on paths rather than on vegetables, and don't sow small seeds right where last year's sunflower stalks rotted down.