Rosemary's Garden - Autumn Cosmos

Elegant cosmos will fill your garden with flowers until late autumn.


Cosmos with its bright hues of pink, orange, yellow, red, purple, chocolate and white is so easy to grow. As long as the daisy-like flowers are deadheaded the plant will provide interest until the first frosts. 

So if you are looking for a flower that will bloom for months and can be grown by simply scattering seeds, cosmos is a fantastic choice.The flowers sit above long slender stems of feathery foliage and form a cloud of colour that will attract bees, butterflies, and birds.

Cosmos can handle drought, poor soil conditions and neglect. A quintessential cottage garden flower, it mixes well with just about everything. Shorter varieties are lovely as edging plants, grow well in containers and make good cut flowers. The taller varieties look good in the middle or back of a border. Depending on the type, they can grow from 45 to 150 cm tall.

Very little maintenance is required. You should not need to water cosmos unless there is a prolonged drought, there is no need to feed them and they can thrive in poor soil.

Although cosmos needs sunshine it likes cooler days and longer nights. You can grow it from seeds, scattering them thinly in June and July or buy them as plug plants. Garden centres have large pots of cosmos that you can buy for an instant display.

When deadheading it is important to cut the stem back to the first leaf rather than pulling the flower head off. Remove the top 10 to 15 cm of the plant to encourage bushier new growth and new flower buds.

Although it is usually grown as an annual, plants may self-seed in the wind. It is also very easy to collect the dried seeds at the end of the season to save for next year. If you stop deadheading in early September and wait for the seeds to become brittle and black they can be stored in an airtight container in a cold, dry place and scattered the following year.

Some popular varieties are:
’Purity’ (100 cm) - A single white which looks lovely in September light.
‘Sensation Mixed’ (120 cm) - A tall mixture in shades of pink, red and white.
‘Sonata Series Mixed’ (60 cm) - Shorter plants with large flowers for the front of a border, a container or for cutting.
‘Sweet Sixteen’ (90 cm) - Pale petals edged in deep-pink, giving each flower a frilly look.
‘Seashells’ (120 cm) - A taller cosmos in a mixture of pinks and whites with cylindrical petals. 
‘Cupcakes’ (90 cm) - This has fused petals that look like cupcake cases.
‘Hummingbird’ (45 cm) - A very new variety with fluted petals on large flowers.
‘Daydream’ (90 cm) - A white cosmos with a pink centre.
‘Xanthos’ (60 cm) - Soft yellow blooms on compact plants, perfect for the front of a border or a container.
'Apollo' (60 cm) - The flowers come in shades of pink, white and purple.

Jobs for August & September

  1. Care for your hanging baskets and containers by deadheading, watering and feeding to keep vibrant displays until mid-autumn.
  2. Cut hardy geraniums to ground level, then feed and water them to encourage new foliage and maybe more flowers.
  3. Remove the leading stems of faded lupins and delphiniums so they continue to flower on the side shoots.
  4. Keep the roots of clematis in the shade and cut out any blackened shoot tips, an indication of clematis wilt.
  5. Keep camellias and rhododendrons moist to enjoy plenty of beautiful flowers in the spring. 
  6. Give hebes and lavenders a light prune after the flowers have finished.
  7. Continue to deadhead plants such as dahlias, delphiniums and penstemons to prolong colourful displays.
  8. Give roses a final deadheading when the flowers have faded and shorten tall stems. 
  9. In September plant allium, daffodil, muscari, scilla, crocus and erythronium bulbs.
  10. Also plant some freesia corms in containers for early, fragrant blooms next spring. 

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