Into the Cosmos
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If I had to choose just one flowering annual to grow in my garden, it would be cosmos.
Lucky for me, I get to ponder such questions. And it wasn’t easy when contemplating the library of choices from the likes of snapdragons, the generous flowering of nigella and, of course, all fun to be had with fleeting seasonal joys like orlaya and poppies!
But cosmos takes the win for a few notable reasons. Firstly, there are so many fun and attractive varieties to explore, both delicate and compact at around 60cm, through to tall and rampaging reaching 120cm+.
No matter what, they seem to have a built-in garden vibe that is joyous and casual, a real plus for those looking to create an informal atmosphere.
Secondly, they are uncomplicated to grow from seed, and it is becoming increasingly easy to pick up all sorts of personality packed varieties in affordable punnets from garden centres.
Lastly, once they are going, they are very tough. They tolerate a higher level of neglect than most, and, provided you keep up the deadheading, they will push to flower right through to the first frosts. All in all, this might just be the flowering plant to entice non-gardeners over the fence.
White cupcake cosmos
Cosmos are easily cultivated from seed and are often considered a good self-seeder without being invasive. In saying this, I have had little luck encouraging self-seeding from my fancier specimens and am suspicious that this reputation comes from the energetic, tall-growing, common pink or white varieties you see leaking out of cottage gardens.
Early spring is a great time to raise seedlings undercover to plant out in late spring/ early summer. Otherwise, wait until very late spring or early summer to simply sow seeds directly in the ground once the risk of frosts has gone.
Once seedlings develop 2–3 pairs of leaves, pinch out the central growing tips to encourage a bushier plant. This seems scary, but you will be on the receiving end of triple the blooms! A step that is often forgotten by many, but reaps the rewards. A healthy plant with good sunlight exposure will mature into a bushy base, with large daisy-like flowers on long slim stems and fern-like leaves.
Cosmos seedheads in need of deadheading to encouraging flowering through to the frosts
To harvest for your vase or encourage endless flowering until the first frosts, simply snip off spent flowers close to where they meet the stalk. The removal of the flower (a potential seed head the plant is aiming to mature) encourages new growth to develop from just above that intersection as the plant attempts to produce more.
Tall plants can get top-heavy and may need staking for support. It is best to put your stakes in when the plant is just a seedling to avoid damaging roots later; after the fact will still work, just be gentle! It’s a sad day seeing your prize cosmos plant lying flat after a blustery front comes through.
As the season cools, halt deadheading and let your flowers go to seed in early autumn. Allow them to dry completely on the plant, before either snipping off heads to store in a dry envelope or scattering in position to encourage a nice self-seeded crop next year. I prefer self-seeded plants that I like and can edit back, rather than bare earth for unwanted weeds to take over.
Cosmos ‘Rubenza” is the start of this show!
Cosmos ‘Pink Lemonade” mixed in with late summer pickings
A pink cosmos ‘Cupcake” in with other summery friends.
Cosmos are susceptible to powdery mildew, often triggered by the stress of underwatering or lack of air circulation. I notice too that it arrives at the end of the plant’s natural life cycle. Once plants look like they are dying, simply cut off at ground level, leaving the roots in the ground to feed the earth and throw in the compost/green bin, leaving that part of your garden clear for self-seeded seedlings in spring, or whatever else you choose to plant.
Some of my personal favourites include the whimsical ‘Cupcake’, which astonishingly looks like paper cupcake wrappers, the ‘Seashell’ mixes that present crazy, fluted petals and ‘Double Click’, with its impossibly frou-frou double blooms.
‘Apricot Lemonade’ has a dainty flower with lovely sunset colours, while ‘Rubenza’, in its deep magenta tones, was a stand-out star in my garden last year. Or, just keep it classic, scooping up punnets of cheerful ‘Sonata’ in pinks and whites from your local garden centre.
This is an expanded version of the article featured in my Stuff ‘Homed’ gardening column for beginners , The Press, Dominion Post and other regional papers on October 7th 2021
All words and images are my own, taken in my home and garden in Christchurch, New Zealand unless otherwise captioned.
