Grow cosmos from fresh seed each year

Martyn Davey, Head of Horticulture and Design, Easton College
Tuesday, November 20, 2012
11:20 AM

Question: Just one of my many beautiful tall cosmos plants has large and small blooms of trumpet petals. Every bloom on the plant is the same. I grow them every year but this is the first like this! If I keep some seeds would it reproduce the same? (Mrs MP Johnson, Bradwell)

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Answer:

Cosmos was one of the first bedding plants I ever grew from seed, and still remains a favourite. It provides height to displays with an airiness few other plants can match. Tall stems carry fine, feathery foliage, each topped with simple, brightly coloured flowers, usually with a brilliant boss of yellow stamens at the centre.

While many bedding plants remain dwarf and compact, cosmos grows taller, swaying above them on the breeze. Seeds are cheap, and these tender summer bedding plants are always reliable, putting on a show right through summer until the first frosts.

I love all cosmos, but some varieties hit the spot more than others. The dwarf Sonata Series has striking flowers, but doesn’t have as much character, to my mind, as the taller varieties.

Plant breeders have had fun with cosmos in recent years, and while those with simple daisy-like flowers are beautiful, something interesting happens when petals turn into tubes, like those on the new variety ‘Sea Shells’, which is where your flowers have come from. I’ve seen some really exciting varieties in commercial seed trials. However, similar cosmos are on sale, such as the double and semi-double flowers on Cosmos Double Click. It grows to 120cm, and is offered in a range of colours. The problem with saving your own seed is the genetic variation will not be just as you hope and you will get a mix of flower shapes and colour. Always grow from fresh seed each year.

Many cosmos come in colourful mixtures, but I love growing varieties in a single colour. Candy Stripe has white flowers with a pink, picotee edge, while bicoloured Daydream has a deeper rose-pink centre, fading to white at the edges. For reds try Pied Piper Red or the new Rubenza. Pink is a popular cosmos colour, and for a striking display try slate-pink Versailles Tetra or apple blossom-pink Sweet Sixteen.

Sometimes there’s just too much colour around, and a fresh breath of pure white dancing at the tips of tall green stems produces a welcome oasis through summer. Firm favourites include cosmos Psyche White and Purity, both offering restful simplicity. And that’s what cosmos does best - simplicity.

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