Sunflower: Sowing, planting and harvest calendar

To sow annual sunflowers under cover, choose good-quality seeds. Sow in spring, for example from late March or in April depending on your climate. Use small pots with drainage holes, filled with light, well-drained potting compost. Sow one seed per pot at the depth indicated on the packet, then cover it.

Place the pots somewhere bright and warm, such as a greenhouse or conservatory. Keep the compost slightly moist without waterlogging it. After germination, continue watering as needed and give young plants plenty of light.

Gradually acclimatise the plants to outdoor conditions before transplanting them once the risk of frost has passed. Choose a sunny, well-drained position. Adjust spacing to the variety, protect young plants from slugs and weed regularly. Nutrient requirements depend on the soil and growing conditions. Adjust any feeding accordingly.

To sow annual sunflowers outdoors, wait until the risk of frost has passed and the soil has warmed up, often around May depending on your climate. Choose a sunny position with well-drained soil. Loosen the surface and remove weeds.

Sow seeds about 2 cm deep, checking the packet instructions. Adjust spacing to the variety: 30–45 cm may suit some, while larger varieties need more room. Water after sowing and keep the soil moist without waterlogging it.

Protect seeds from birds and young plants from slugs. Stake tall varieties if necessary, using soft ties that do not constrict the stems. You can leave faded flower heads on the plants to feed birds, or save some to harvest the seeds.

Mark the sowing positions so you do not mistake the young shoots for weeds in the border. If several seeds germinate in one spot, thin them to one strong plant while disturbing its roots as little as possible. For tall sunflowers, consider the shade they will cast on neighbouring crops before choosing your sowing line. Check the supporting ties regularly as plants grow: a tie that fitted well at first can become too tight as the stem thickens. Leave enough room to reach the plants without trampling the sowing sites.

Annual sunflowers flower in summer, sometimes into autumn, depending on the variety, sowing date and climate. Flowering is not limited to August or a fixed two to three weeks: a branching variety can produce several flowers in succession. Colours range from yellow to cream, orange or red, depending on the cultivar.

Choose a sunny position and well-drained soil. Water as needed, especially in hot or dry weather, to prevent the soil from drying out. Plants in pots need more frequent checking.

Organic mulch helps retain moisture; keep it away from the base of the stems. Adjust feeding to the soil and growing conditions, following the instructions for any products you use. Stake tall varieties if necessary.

Before cutting off faded flowers, decide whether you want to keep seeds for birds or future sowing. Branched varieties may continue opening side buds, but a stem carrying one large head does not behave like a small bush with many flowers. Make clean cuts without damaging buds that are still present. After windy weather, check the stake's stability and carefully adjust ties where needed, without trying to force a badly bent stem upright. Keep the support clear of developing flowers so they are not rubbed by a loose tie.

Harvest sunflower seeds when they are mature, not as soon as they form. The timing depends on the variety, sowing date and climate. Wait until the petals have faded, the back of the flower head turns yellow then brown, and the seeds are well filled.

Cut the mature head with a length of stem and let it finish drying somewhere dry and well ventilated, sheltered from rain. Then remove the seeds by gently rubbing the head.

For future sowing, store only thoroughly dry seeds in a paper bag somewhere cool, dry and dark. Check their condition during storage. You can also leave some heads on the plants to feed birds. Seeds saved from F1 hybrids will not reproduce the original variety faithfully; cross-pollination between varieties can also change the next generation.

Spread the heads out during drying instead of stacking them while still damp. Turn them and inspect the backs to spot any mouldy patch promptly. After extracting the seeds, sort out debris, empty shells and damaged seeds. Label each packet with the variety and year, keeping seed for sowing separate from the supply intended for birds. Closing a packet while the seeds are still moist encourages deterioration, so finish drying them before storage. Check the packets again later rather than assuming that their condition cannot change after the first inspection.