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Cosmos growing tips

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White variant of Cosmos Cupcakes
Mandy's own white Cosmos Cupcakes, July 2015

It’s the Year of the Zinnia but Cosmos are fighting back!

It’s easy to see why cosmos are so popular, partly due to breakthroughs in breeding which have led to new varieties such as Cupcakes and Lemonade, but it is also down to great garden performance, according to Thompson & Morgan.

Born out of a chance find in a California back yard in 2007, gardener Diane Engdahl discovered an unusual cosmos flower and sent the seed to Thompson & Morgan.

Instead of its flower being made up of individual petals, like most cosmos, the petals of this bloom were fused together, creating one single ‘cup’.

For nearly 10 years, plant breeders have been ‘fixing’ this new trait across the colour range, developing new shades and refining the shape. During last year’s Year of the Cosmos, visitors to RHS Garden Wisley named their favourite garden cosmos as part of the Royal Horticultural Society’s People’s Choice Competition. Cosmos bipannatus ‘Cupcakes White’ came out on top of the 84 varieties on show.

Cosmos Lemonade

Also from Thompson & Morgan’s own breeding is Lemonade, a multi-flowering subtle yellow cosmos with a striking white eye, T&M’s plant breeding team took a very bright yellow, but late-flowering Japanese variety and crossed it with earlier-flowering cosmos with better, shorter habits. The resulting delicate, yellow blossoms of

Flowers are produced throughout the summer on short to medium-high, branching plants, great for patio pots or as a border filler.  Cosmos Lemonade also makes a good cut flower and looks stunning in a vase.


Top tips for growing cosmos from seed

  • Sow seeds in a heated greenhouse or propagator in April.
  • Good light is important to prevent leggy seedlings.
  • Young plants can be planted out after the very last frosts, usually in late May/early June.
  • Regular dead-heading will promote flowering right up to the first frosts.
  • When dead-heading, cut the stem right back to the first leaf rather than just pulling the flower head off.
  • Seed can be planted outside, where you’d like them to flower, in May or early June.

Thompson & Morgan also offers a number of varieties as plants which, depending on the time of delivery, can be planted straight out into the garden, or they can be potted up and grown on before transplanting.

  • Cosmos Cupcakes White, height: 120cm (48″). Spread: 60cm (24″) – 1 packet (30 seeds) £1.99.
  • Cosmos Cupcakes Mixed, height: 120cm (48″). Spread: 60cm (24″) – 1 packet (100 seeds) £1.99.
  • Cosmos Lemonade, height: 60cm (24in). Spread: 40cm (16in) – 1 packet (30 seeds) £2.49.
  • Cosmos Lemonade: 30 garden-ready plants £14.99.

 For further information on growing cosmos, go to www.thompson-morgan.com/cosmos-article to read an article by Graham Rice taken from The Seed Raising Journal, or visit the half-hardy annuals from seed page.

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