A short guide to sunflowers

They’re easy to grow, beloved by birds and insects - and best of all, they’ll put a smile on your dial. Who doesn’t love sunflowers?

Leggy: some sunflowers grow over 3m tall, but there are dwarf varieties too

Want happy, cheerful faces around you? Plant sunflowers. They also have some fascinating science and provide edible petals and seeds.

Both the common name and botanical name, Helianthus annuus, reference the sun – they look like miniature suns but sunflowers also track the sun. Young plants follow the sun each day from east to west, then reset overnight. It’s called heliotropism. They do this by having different growth rates on each side of the stem: during the day the east side cells grow faster than those on the west; at night the opposite happens. Once the flower heads open and their stems are fully elongated, they stop moving and all face east – that’s why fields of them can look so spectacular. Facing east allows the morning sun to warm them faster, attracting more pollinating insects such as bees.

Each huge flower comprises an outer ring of ray florets or petals surrounding a central disc of thousands of tiny florets. These florets, and later the seeds, are arranged in clockwise and anticlockwise spirals that (mostly) follow the mathematical Fibonacci sequence. The leaves are arranged in reverse spirals, maximising sun exposure to each leaf.

Originally from the Americas, sunflowers are summer annuals that can grow in most parts of Australia. Plant seeds from spring to early summer, but in cold areas wait until frosts are over and in the tropics grow them in the dry season. ‘Giant Russian’ can reach 3-4m tall with colossal yellow flowers up to 50cm across. Dwarf types (25-40cm tall) are suitable for pots.

‘Teddy Bear’ sunflower

Compact (60-90cm) types don’t need staking, but the standard (1-1.5m) and tall giants (2-3m) need staking and shelter from wind to prevent them bending and snapping. The traditional bright yellow colour has been expanded to lemon, gold, orange, bronze, russet reds, and bi-colours, and there are doubles such as the fluffy gold ‘Teddy Bear’.

Keith White of Copsley Ornamentals has been breeding ornamental sunflowers for nearly 20 years. His FleuroSun collection includes branching types, new colours such as peach and lilac and pollen-free sunflowers that don’t trigger allergic reactions. Being infertile, they don’t produce seeds, but the blooms last longer and still contain nectar for bees.

To grow sunflowers, sow seeds into fertile soil in a sunny spot where you will see the east-facing blooms. Keep moist; they should germinate in 8-14 days. They look best in a mass and cross-pollination helps seed production. Supply plenty of fertiliser and water; stake as needed. As the seeds form they become bird magnets, especially for cockatoos. If you want the seeds for eating or to plant next year, cover the heads with a fine mesh bag. When they start to die, cut with a stem “handle” and store upside down in a cool spot until the seeds can be tapped out.

Good to know

Sunflowers can remove heavy metals such as lead from the soil; they were used around Chernobyl to remove radioactive cesium and strontium

A typical sunflower contains 1200 seeds

Seeds are nutritious, with about 20 per cent protein. Grind them to make a peanut-alternative butter

Q&A

The olive tree in my small city garden hasn’t had fruit for three years. Is it a result of cutting back the tree each year, or the wrong environment? Jan Holmes, Brisbane

Olives prefer a Mediterranean climate of hot, dry summers and cool winters. Some varieties such as ‘Arbequina’, ‘Arecuzzo’ and ‘Manzanillo’ can fruit in subtropical areas but not reliably. You need cross-pollination from a second variety (although ‘Arbequina’ can self-pollinate). And they need full sun to flower in the first place. Prune in autumn or after harvest. Heavy pruning can reduce the next year’s crop.

I have access to a large load of mulch made from branch trimmings. About a third is eucalyptus leaves. Is it safe to use on the garden immediately? Julia O’Brien, Melbourne

When woody materials decompose they use up nitrogen. Placed fresh on gardens, they can draw it out of the soil, causing deficiencies. Fresh leaves contain nitrogen to help balance the high-carbon woody materials, but eucalyptus leaves are best composted to help break down the volatile oils they contain. Ideally stockpile your mulch for six weeks, adding a nitrogen source such as blood and bone or manures, and keep moist.

My tall agave has two small offspring at its base. Can I separate and pot them? Maria Garvey, by email

As agaves grow longer stems they produce new “pups” at the base. You can easily detach these and pot them up – they’re very tough. If you cut off the tall stem at the base it stimulates growth of the pups and you can replant the big head straight into the ground, shortening the stem to the desired length.

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Send your questions to: [e-mail] or Helen Young, PO Box 3098, Willoughby North, NSW 2068. Website: helenyoung.com.au. The best question for September wins a Karcher WD2 Premium wet and dry vacuum cleaner worth $119