Sunflowers are vibrant flowers that make you feel happy. They have big, bold, and brightly coloured blooms and petals that resemble the sun’s rays. This ‘How to Grow’ guide has everything you need to know about sowing, growing, and caring for sunflowers.
What are Sunflowers?
Common Name: Sunflower
Botanical Name: Helianthus annuus
You would be surprised to know that the common sunflower is, technically, a herb instead of a flower. As a herb, it is unusual as it is an annual instead of a perennial plant.
Native to North America, this herbaceous annual plant is part of the aster (daisy) family. Almost 70 common sunflower varieties are available in different colours and flower sizes.
Popular heirloom varieties
Sunflowers can produce a single or multiple flower heads on top of a thick, tall stem. Some varieties reach up to 3 metres in height, and giant sunflower varieties can exceed 4 metres.
Sunflowers get their name because they track the sun. Young plants slowly turn to follow the sun each day from east to west. Overnight, they re-set their position, ready for the next day. This process is called heliotropism. Sunflower fields look so beautiful because the flowers are turning, in unison, to face the sun’s direction. Helia (from Helianthus annuus) comes from the ancient Greek word for sun, hḗlios.
Interestingly, sunflower florets and seeds have spirals similar to the mathematical Fibonacci sequence.
Sunflower is an edible flower and oilseed crop. It produces sunflower oil, bird seed, edible kernels, snacks, and confectionery. Popular as sprouts and microgreens, these greens have a nutty flavour and crunchy texture. Add them to salads, smoothies, wraps, or stir-fries.
Although you can grow sunflowers in poor soil, including clay or sandy soil, it is best to grow them in well-drained soil. Sunflowers are heavy feeders and deplete the soil, so add a slow-release fertiliser containing trace minerals. Add organic matter such as compost or aged animal manure. These extra nutrients, combined with well-drained soil, will boost the growth and size of the flower.
When growing sunflowers in containers, use a premium-grade potting mix and choose a container of at least 40 litres. Ensure ample sunlight and select a variety that suits container growing.
When to Sow
Sow seeds directly in the garden 10 mm deep.
To produce sunflowers with smaller flowers, allow plant spacing of 15 cm. Allow at least 35 cm plant spacing to grow sunflowers with larger flowers.
Row spacing should be at least 2 metres.
Ensure the soil is moist (not too wet or too dry).
Seeds germinate in 7-14 days when the soil is 21 – 30°C.
Protect seedlings from harsh conditions and pests until established.
Fill trays with good quality seed-raising mix.
Sow to a depth of 10 mm.
Ensure the soil is moist (not too wet or too dry).
Seeds germinate in 7-14 days when the soil is 21-30°C.
Transplant seeds to the garden when they reach 5-10 cm tall.
Plant 15 – 35cm apart, rows at least 200 cm apart.
How to Sow
Sunflower seeds don’t need soaking or stratification before sowing. You can sow seeds directly into garden beds, trays, or containers, transplanting them into the garden once established. Seeds need warm soil (21-29°C) for germination.
Although you can raise seedlings and then transplant them to your garden bed, it is best to sow seeds directly into the garden. Sunflowers have long, fast-growing taproots that can become stunted if grown in a small container. Stunted growth will prevent your sunflowers from reaching a mammoth size.
How to Grow
Allow 15-35 cm spacing between plants. Tighter spacing will produce a smaller flower with thinner stems, making it ideal for mixed bouquets. Wider plant spacing produces larger flowers suited to flower bunching.
Sunflower plants have taproots that can grow up to 120 cm long. Plants require occasional but deep, thorough watering. Once established, sunflowers can tolerate brief periods of drought. However, they grow best if the soil moisture level is consistent (not too wet or dry).
The optimum times for watering are early morning and late afternoon, as this reduces evaporation from the day’s heat. Check the moisture levels by inserting your finger into the soil approximately 5 cm. If the soil feels dry, then the plant needs to be watered. Other signs the plant needs watering are when the leaves are yellow, fading, drooping, or wilting.
Avoid overwatering, as it can lead to plant disease, root rot, and fungus infestation.
Depending on the size, sunflower plants may require staking. The thick-stemmed, tall varieties with sizeable flower heads need support due to their weight. Many staking options are available at garden centres, including trellis or bamboo stakes. You can make a trellis with anything sturdy enough to support the plant as it grows. You will also need twine to tie the plant to the trellis as it grows.
Sunflowers are susceptible to various threats, including Fusarium fungi and downy mildew. Cover the flower heads with netting when they are nearly ready for harvest to protect them from birds.
Harvesting and Preserving
Sunflowers take approximately 90 days to harvest. To collect seeds, deadhead (trim) the spent sunflower blooms. Hang the flower heads upside down in a cool, dry place until the seeds can be removed with light tapping.
Place the flower head in a large container and hit it against the walls of the container to dislodge the seeds. Use a fork to scrape the remaining seeds out of the sunflower head.
Eat seeds raw or roasted. If you plan to replant the seeds, dry them well and store them in an airtight container until you are ready for planting.
Avoid planting near potatoes and pole beans, as they inhibit each other’s growth.
Sunflowers are a natural trellis for climbing vegetable varieties such as cucumbers and corn.
Sunflowers protect zucchinis, pumpkins, and squash from aphids.
The protein-rich nectar attracts pollinators, including bees and beneficial insects, to your garden.