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Name: cosmos, garden cosmos, Mexican aster, Cosmos bipinnatus, sulfur cosmos (Cosmos sulphureus).
Height: 20cm-120cm.
Plant type: mostly annual, a few perennial.
Climate: warm and cool temperate, subtropical, tropical and arid.
Soil: moist, well-drained soil enriched with compost.
Position: full sun.
Foliage: lime-green or grey-green, finely divided, fern-like.
Flowers: masses of daisy-like or cup-shaped blooms appear from summer to autumn in vibrant and soft shades of white, pink, carmine, red, yellow and orange. Hybrids may be bicoloured with single, semi-double or double flowers with entire or fused petals.
Feeding: liquid feed regularly with a fertiliser that’s specially formulated for flowering plants.
Watering: water regularly.
Cosmos is the quintessential cottage-garden flower. It produces masses of charming, daisy-like or cup-shaped blooms on slender, upright stems. The foliage is airy and fern-like, further adding to its wildflower-garden appeal. Traditionally, it grows to 100-120cm tall, but shorter forms are available.
Cosmos varieties feature a wide range of flower shapes and colours. The species form has a single, daisy-like bloom, but hybrids may have single, semi-double or double flowers with entire or fused petals. They can be bicoloured, too.
The young leaves and flowers of Cosmos sulphureus are edible, provided they have been organically grown. Other cosmos flowers are not considered edible – while they’re not toxic, the taste is not pleasant.
Cosmos is a magnet for pollinators, so is an ideal choice if you’re looking to encourage bees and butterflies into the garden. Mass plant in garden beds, along borders or in pots for a dramatic display. Cut flowers regularly and arrange in vases or bouquets.
In most climates, you can sow cosmos seed in spring (once the chance of frost has passed) and early summer. In warmer climates, sow in winter. Sow in trays or directly into garden beds enriched with compost, lightly cover with soil and keep moist. Germination can take 7-21 days.
Thin out seedlings, allowing 30-60cm between plants, depending on their expected eventual height. Once seedlings have formed three pairs of leaves, pinch out the growing tip to encourage bushy plants that will produce more flowers.
Staking is required for tall plants (greater than 60cm); use thin stakes and garden twine.
Deadhead spent blooms regularly to promote new buds. Plants will often continue to flower well into autumn or until the first frost. To deadhead, cut the stem just above the foliage.
Keep plants well watered as they grow, especially during dry conditions. Spread a layer of organic mulch over the soil to help conserve moisture.
Liquid feed fortnightly with a fertiliser that’s specially formulated for flowering plants.
Cosmos usually takes 10-14 weeks from seed to flower. To harvest cut flowers, pick when the petals are starting to open but not fully flattened. Place in a vase and change water daily.
Slugs and snails love tender young seedlings. Use physical barriers or slug and snail bait to help keep them away. Aphids and spider mites are also common pests and can be controlled with organic sprays.
Species cosmos will readily self-seed and flower the following year. Hybrids may seed, but they’re unlikely to produce the same desirable traits as their parent plants.
Billy buttons: a cute native perennial with pompom yellow flowers on tall, slender stems.
Cuphea: this hardy groundcover is covered with tiny white or pink-purple blooms throughout the year.
Angelonia: a floriferous annual or perennial with spikes of purple, red, pink, blue or white flowers.
Check out our huge range of flowering plants now and get your garden growing!
Photo credit: Getty Images
Asbestos, lead-based paints and copper chromium arsenic (CCA) treated timber are health hazards you need to look out for when renovating older homes. These substances can easily be disturbed when renovating and exposure to them can cause a range of life-threatening diseases and conditions including cancer. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer or visit our Health & Safety page.
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