Pink cosmos flowers

Flowering at Last: Cosmos

Posted on by Ann Mackay

This year I decided to grow cosmos ‘Seashells’ (above), but it has taken a long time to come into flower. For a while, I didn’t think there would be any flowers at all. Now, however, the first few flowers have opened and there are plenty more buds for flowers to come.

I was worried that I had sown the seeds too late. (Sometimes there are just too many things wanting to be done at the same time in spring.) Even so, I hoped for a late show of flowers from them and they haven’t let me down.

I belong to a gardeners’ group on Facebook, and some of the members had been discussing the lateness in flowering of their cosmos plants. One of the group came up with the information that it’s simply because the plant is sensitive to day-length and needs a short day (long night) to be able to produce flowers.

That’s something that I would never have thought of before. Living in the UK, I tend to assume that flowers will want the longer days of summer. (I imagine that people who live in areas where cosmos are native or naturalised will be much more aware of the effect of the day-length.)

Apparently there are new varieties which don’t need the short days and can flower earlier in the summer. So next year I can either buy these seeds, or relax, take my time, and sow the older varieties a bit later. Or maybe try both – you can never have too many pretty flowers!

Dark pink cosmos flower
A dark pink cosmos photographed in a garden I visited last year.

Published by Ann Mackay

Photographer, mixed-media art adventurer and completely daft about plants.......

21 thoughts on “Flowering at Last: Cosmos”

    1. Thanks Indira! The colour is especially welcome now, when most of the other flowers are finishing (or have already gone) for the year.

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  2. My cosmos have been flowering their socks off all summer, but run out of energy now. This one is a very pretty pale pink. I found the white ones produced many more flowers than the pink ones I bought. Interesting thought about daylight hours.

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    1. I’ve read (spending too much time Googling…) that the more mature plants are less affected by daylight hours and that if you’ve managed to sow them very early, they will flower earlier, whatever the day length is. So, I suppose that if you got a really early sowing done and another at either ‘normal’ time, or later, you’d have flowers right through. For someone who finds it difficult to be organised in spring (I never am), it’s nice that it doesn’t seem to make much difference if you’re a bit late sowing the seeds. But I should find out about the varieties that aren’t affected by day-length. They’d be so much easier!

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  3. This is interesting. My current post is of Texas coneflower, which blooms in May (give or take), then stops blooming until September or so. I’d assumed it was the heat that caused the blooms to cease, but now I’m thinking hours of daylight may be a factor.

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    1. It might! Though in this case, it seems to govern when the flowering starts. I wonder what the reason for it is? (Maybe someone will be able to tell me! 🙂 ) And I must go and have a look at your post – coneflowers are lovely.

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    1. The Facebook gardening group that I’m in is great. Lots of us had been wondering why cosmos could be so slow to flower and one of the members was able to come up with the answer – web friends can be a great source of info! (The phenomenon is called ‘photoperiodism’.)

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    1. I’m glad to have some flowers this late in the season. The wind has been really rough for a few days and they’ve had a bit of a thrashing but have survived – yay!

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      1. I can appreciate a high wind down here where I live. I have lost several plants to hurricanes over the years. Any plant that survives high winds deserve a little extra TLC IMHO!

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      2. Yikes, I really can’t imagine having to cope with hurricanes! (Though there was one infamous one in the UK some years ago…lots of trees were lost and the weather forecaster who said it wouldn’t happen must have felt silly ever since.) But yes, plants that bravely come through bad weather deserve all the help they can get. 🙂

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    1. Thanks Jill! Cosmos does seem to do the unexpected – I had plants that grew much taller than they were supposed to before flowering too. I’m just grateful that these haven’t been shredded by the rough weather of recent days!

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  8. Your photos are beautiful, Ann. This is one flower we share, but my experience differs from yours. Our cosmos starts to bloom in late July and doesn’t stop until the frost puts a halt to its exuberance. Every year they cover more ground, which makes us as a happy as the many insects that frequent them.

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    1. Thank you Tanja! I think that we used to be have cosmos that bloomed sooner – maybe because we bought young plants that had been started off indoors, so they were mature enough to flower earlier. It seems that plants that have had the chance to mature early are less affected by day-length. (According to what I’ve come across through my time spent with Google… 🙂 ) Do yours self-seed? They wouldn’t be able to hear, so couldn’t spread in the UK that way…though if our climate keeps changing, who knows!

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