NZ Gardener cosmos trials
Lynda Hallinan goes crazy for carefree cosmos, raising 20 varieties of these easy-care daisies from seed in her latest home garden trial.
Lynda Hallinan finds the best easycare cosmos for every situation.
Honestly, what’s not to love about cosmos?
For a few dollars worth of seed, you can fill your garden with a carefree constellation of these colourful daisies all summer long (and well into autumn, provided a plague of powdery mildew spores doesn’t intervene to knock them down before Jack Frost shows up to finish them off).
Cosmos are the ultimate flowers for low-budget, highimpact borders. There are petite performers for popping into pots and lovely long-stemmed varieties for vases. They come in a range of forms, from elegant singles to frilly doubles, with novelty tubular types and cup-shaped charmers with fused petals that look like they have been neatly snipped into a circle with a pair of pinking shears.
There are 36 species, most of which are Mexican, plus dozens of cultivars of the most common garden species,
Cosmos bipinnatus. As well as the traditional potted-colour shades of candy pink, white and bright magenta, in recent years the cosmos colour spectrum has evolved to include apricot, lemon yellow, wine red and two-toned picotees.
Cosmos are irresistible to honeybees, monarch butterflies and beneficial insects such as lacewings and parasitic wasps. At night, their petals offer a futon bed to napping bumblebees; I accidentally shake them awake if out picking flowers too early in the morning.
Despite – or perhaps because of – their friendly, no-fuss personalities, in our gardens cosmos are commonly considered cast members rather than the stars of the show. They have one of the shortest Wikipedia entries for a popular plant: just 373 words, none of which are even vaguely poetic.
They do get the kudos they deserve on the Flower Essence Society website flowersociety.org, in a comprehensive plant study written by Patricia Leslie. She compares cup-shaped cosmos to satellite television dishes turning to receive the sun and notes how, when the wind blows, the flowers turn their backs and use their petals as a parasol to protect their fertile midriffs, indicating “a character of openness and receptivity”.
A SOFT SPOT FOR COSMOS
I can’t remember a time when I didn’t have a patch of Cosmos bipinnatus in my Hunua garden. They dance up to my front door, flinging their limbs out of a bed of Lomandra ‘Titan’, white geraniums, cream collerette dahlias and Nicotiana sylvestris.
Cosmos will always be special to me as they feature in all my wedding photos. Ten years ago, I walked up the aisle in late February. In the weeks leading up to the ceremony, I massplanted the long borders around our new lawn with wildflowers and white cosmos. The wildflowers were seeded direct but all the cosmos – several hundred seedlings – were raised in punnets so I could tuck them into any gaps at the last minute.
By mid-January, the wildflowers were barely ankle-high and I began to panic that I’d sowed them too late, so I installed a front row of white cosmos and gave them a generous scattering of Nitrophoska Blue fertiliser.
The cosmos grew waist-high with sunflower-thick stalks and thick ferny foliage, completely swamping the wildflowers. It took family friends an entire day to deadhead them before we got hitched.
Cosmos are ridiculously easy to grow – all they ask is a sunny spot with reasonably free-draining soil – but my wedding garden taught me two important lessons.
One: cosmos don’t need fertiliser as too much nitrogen impedes their flowering and turns them into chunky clumps rather than filigreed ferny gap-fillers.
And, two: cosmos are susceptible to mildew if planted too closely, so space seedlings at least 30cm apart. Within a week of our wedding, my white cosmos borders were a sight for sore eyes, their ankles defoliated, their branches browned off by fungal spores. They’d done us proud on our big day, but only just.
Cosmos is one of the most foolproof annuals to raise from seed and, once you’ve seen them through summer, you’re invariably rewarded with a rash of free seedlings the next spring.
By late summer, hot colours predominate in most picking gardens, but cosmos is a notable exception. It can be relied upon to supply all the pretty pastel shades required for summer bridal bouquets.
Cosmos have a tendency to grow tall with straight main stems that can break unless staked. To encourage bushiness and more balanced branching, nip out the central tip when transplanting, and pinch back some of the side growths early in the season.
A GROWING SEED SELECTION
Cosmos is definitely increasing in popularity if the number of varieties listed by local seed companies is any indication. I collected 20 varieties to sow, and by the time this is printed there will be new names to seek out. Kings Seeds is launching the apricots, peaches and cream ‘Apricotto’ in its 2021 catalogue, while Debbie Sisam at Puriri Lane Nursery in Drury will have plants of vintage crimson-pink ‘Antiquity’ available next spring. Egmont Seeds also has a sassy new picotee cosmos called ‘Capriola’ on offer. This is described as boasting “an extraordinary colour pattern”, being white with a light rosy-red rim and a dark purple-red centre.
HOW TO SOW COSMOS
In mid-November, I sowed 15 types of Cosmos bipinnatus, four strains of orange and yellow Cosmos sulphureus and the perennial chocolate cosmos,
Cosmos astrosanguineus, in trays of pre-dampened potting mix. Cosmos seeds are large and easily handled, so fine seed-raising mix is unnecessary.
I sprinkled the seed over the mix and covered it with medium-grade vermiculite. (This also isn’t necessary, but I had a beanbag-sized sack of the stuff leftover from germinating chillies and zinnias.) Fresh Cosmos
bipinnatus seed germinates reliably and most varieties took 3-5 days to sprout after 48 hours on a heat pad. I had a near-perfect seed strike from ‘Candy Stripe’, ‘Sea Shells’ and ‘White Gazebo’, which sprouted as thick as grass. With the fancier cultivars, such as frilly ‘Double Click Mixed’, there were noticeably fewer seeds in the packet but all of them germinated. ‘Lemonade’ was the slowest of the
Cosmos bipinnatus varieties to sprout (10 days) but Cosmos astrosanguineus was such a slowpoke (four weeks) that I’d almost written it off by the time it raised its head.
The pink-edged ‘Picotee Mix’ and unusual faded-red ‘Rubenza’ had the fewest number of seedlings, at 14 and 16, yet both went on to bloom magnificently in my garden, so it would be churlish to complain.
My trays of Cosmos sulphureus took slightly longer to sprout (7-10 days) and the seedlings were smaller. The foliage looks more like marigolds than ferny Cosmos bipinnatus.
This species, with its bold coloured blooms of red, orange and gold, is better suited to wildflower gardens than tidy borders; in the past I’ve simply chucked the seed at the soil and let it pop up where it wants to.
In mid-December, I potted up all my cosmos seedlings to grow on, as I’d been having a devil of a time with birds scratching up tiny seedlings. All my cosmos was transplanted during the week after Christmas, then left to it. At this point, the healthiest plants were seedlings of ‘Cupcakes Mixed’.
LYNDA’S TRIAL FAVOURITE: ‘DOUBLE CLICK MIXED’:
Is it sacrilege to choose the least cosmoslooking variety as my favourite? I think not. As soon as ‘Double Click Mixed‘ started blooming, I was instantly enamoured by its ruffled blooms in clear pink, cream, magenta and burgundy with gold centres. The fluffy long-stemmed flowers, which remind me of a chrysanthemum crossed with a collerette dahlia, are excellent for picking and are produced in abundance on tall, healthy plants. It was flawless, floriferous and fast to flower, taking 80 days from sowing. From Egmont Seeds.
BEST YELLOW: ‘LEMONADE’:
Of the two pale yellow varieties I sowed, ‘Lemonade‘ (Egmont Seeds) produced noticeably stronger, bushier plants that flowered for a longer season than dwarf ‘Xanthos’ (Kings Seeds). The large flowers have shaggy petals of apricot-yellow with blush-pink around their centres, giving them a slightly vintage look. ‘Xanthos' is clearer lemon with a gold centre and has more classically cosmos-shaped flowers than ‘Lemonade‘. As a dwarf variety (up to 40cm in my garden) it’s better suited for pots or the front of borders. I’d grow both of these lovely lemon varieties again.
PRETTIEST PICOTEE: ‘CANDY STRIPE’:
Picotee flowers have a rim of one colour that contrasts the rest of the petal. I sowed two types of picotee cosmos, ‘Candy Stripe’ (Kings Seeds) and ‘Picotee Mixed’ (Egmont Seeds). ‘Candy Stripe’ had an excellent germination rate, whereas I only ended up with 14 ‘Picotee Mixed’ seedlings. ‘Candy Stripe’ proved to be one of my best trial performers with tall plants (1m+) smothered in flowers for months on end. There was lots of variation among both varieties, with some flowers edged thinly in crimson and others looking like they’d been dipped in pink dye.
BEST FOR GARDEN BORDERS: ‘WHITE GAZEBO’:
With large white flowers produced en-masse all summer long on tall (1m+) plants, ’White Gazebo’ (Kings Seeds) was the best overall garden performer in my trial. It was in full bloom before most of its siblings even budded up and it kept flowering well until late March.
However, if you prefer a traditional mix of white, pink and crimson cosmos in your flowerbeds, the McGregor’s seed range includes the dwarf ’Gazebo Mixed’ blend. I’d also recommend ’Sonata Mixed’ (Egmont Seeds), ’Unique Mixture’ (Kings Seeds) and ’Sensation’ (Yates Seeds). In my trial, ’Sonata’ produced a high proportion of gorgeous candy floss-pink flowers with carmine circles around their gold centres.
CUTEST COSMOS: ‘CUPCAKES MIXED’:
When I first planted ’Cupcakes Mixed’ cosmos a couple of years ago, I was captivated by their cute shape. The petals of this selection are fused together to form a shallow bowl-shaped bloom with crimped sides, like a paper patty pan case, and zigzagging edges. And if that’s not delightful enough, at least half the plants in my trial bed produced double flowers with an extra ring of internal petals, some in contrasting colours. A charming talking point, ’Cupcakes Mixed’ (Egmont Seeds) is tall (up to 1m) with a good range of colours including very pale pink.
The other notable cosmos with a quirky form is ’Sea Shells’ (from Egmont Seeds, Kings Seeds and and McGregor’s), which has fluted petals rolled up into individual tubes. But ’Sea Shells’ was the slowest of all the varieties in my trial to bloom and, despite one of the best germination rates, my strong, stocky plants only produced three flowers in total by the time Sally Tagg arrived to photograph them, hence their absence from this page!
CHIC COLOUR: ‘RUBENZA’:
’Rubenza’ (Egmont Seeds and Yates Seeds) grows to 70cm with large, single flowers that open dark blood red but gradually fade to matte brown-pink. That mightn’t sound particularly attractive but it’s beautiful. For another subtle but unusual cosmos, try pale peachy pink ‘Apricot Lemonade’; buy plants from Puriri Lane Nursery next spring.
A BOX OF CHOCOLATES
While Cosmos bipinnatus is a cheerful sight in summer borders, the species that sophisticated gardeners seem to love most is Cosmos astrosanguineus.
A Mexican native, famously known as “chocolate cosmos”, it has small, shimmery daisies in brown velvet. In NZ Gardener’s online magazine
Get Growing, Rachel Clare described it as smelling like “a cocoa-scented flower from Willy Wonka’s factory”, but I’ve sniffed many a plant over many years and never caught a whiff of Cadbury’s Bourneville Cocoa. The aroma is said to be strongest when gently warmed – or should that be melted? – by the sun, but my nose has found no evidence in support of this. 60
I quizzed my gardening friends on Facebook and opinion was divided between the nasal yays and nays, with some people adamant that, on warm, still days if you sink your nose deep into a newly opened flower or gently caress its petals, there’s an undeniable aroma of milk chocolate.
“Yes, I have grown it in the past and I can smell chocolate – mind you I’d smell chocolate miles away,” joked Maxine Raine. “I could smell it as soon as I drove up the driveway,” added Nicola Painter. “Unfortunately, so could the chickens. They ate it.”
Others weren’t as effusive in their praise, comparing the “sweet and thin” fragrance to the smell of cheap chocolate. “More like chocolate essence than actual chocolate,” said Rosalea Webby, and Jan Bentley was also doubtful. “Very underwhelming, just a slight vague chocolate smell.”
Several gardeners thought the common name referred only to the flower colour, rather than its scent, because they’d never smelled a thing.
(As an aside, we also had a chat as to whether chocolate-brown boronia,
Boronia megastigma, deserved its fragrant reputation, as I can’t smell it either. Port wine magnolias also seem to foil many noses, but as my Michelia
figo hedge reeks deliciously of Juicy Fruit gum, I now know my olfactory system isn’t completely dysfunctional!)
Would anyone grow chocolate cosmos if not for its name? I’m not convinced. In the garden it is short, scrawny and easily lost. Quite frankly, I prefer Salpiglossis sinuata ‘Chocolate Royale’ (from Kings Seeds or Puriri Lane Nursery) for that exotic colour. Garden designers often specify
Cosmos astrosanguineus for the front of naturalistic borders or as a foil for ornamental grasses. It looks dainty mingling with Poa cita, the red form of Carex comans, Libertia peregrinans, Astelia ‘Alpine Ruby’ and twisty dwarf brown ‘Jack Spratt’ flaxes.
Chocolate cosmos has an intriguing history. Introduced to Britain in 1861,
Cosmos astrosanguineus debuted in the 1885 Thompson and Morgan seed catalogue as “black dahlia”. But over the next century it fell in and out of fashion, until there was just one sterile
As cut flowers, cosmos aren’t longlasting – you’ll be lucky to get a week from double varieties and a few days from single daisies – but the plants flower so prolifically that there are always many more buds to come. Try to beat the bees to the blooms as after pollination their lifespan is further reduced.
clone left – and all the plants sold in the US and the UK were subsequently propagated by tissue culture from it.
Rumour had it that deforestation had caused the complete annihilation of Cosmos astrosanguineus in its native Mexico, but this wasn’t true. “This myth that the plant was extinct really shows the arrogance of the West at the time,” chuckles the renowned West Auckland plant breeder Dr Keith Hammett, “as nobody thought to actually ask a Mexican botanist. Not only were there populations in the wild, they knew where they all were.”
What’s more, it wasn’t even extinct here. In 1990, the late Otago genetics professor Russell Poulter found two seeds had set on his supposedly sterile plants. He sowed these and spent several years cross-pollinating the resulting seedlings with the lofty aim of returning plants to Mexico.
When interviewed for a 2017 article in the RHS journal The Plantsman,
Russell noted that while he succeeded in restoring their fertility, he had also “discovered the genome was full of mutant characteristics that needed to be got rid of.” As well as odd-looking petals, one of those characteristics was a lack of chocolate scent.
Russell kept at it, selecting and crossing seedlings until he was ready to release an improved form known as ‘Pinot Noir’ in the late 1990s.
Dr Keith Hammett subsequently crossed ‘Pinot Noir’ to produce ‘Dark Secret’, ‘Eclipse’ and ‘Spellbound’. Of the trio, ‘Spellbound’ had the richest strongest chocolate scent, but ‘Eclipse’ had the biggest (up to 5cm) flowers.
Keith says chocolate cosmos should indeed smell of chocolate and though he admits to having “largely lost my sense of smell for sweet peas”, he has no issue with Cosmos astrosanguineus.
Mind you, he’s breeding a new dahlia at the moment that he reckons is a chocolate cosmos lookalike, with no fragrance of course.
In the past, botanists have bickered over whether Cosmos atrosanguineus should be classified as a bidens daisy or a dahlia (established plants grow fleshy, tuberous roots like a dahlia), but DNA testing has confirmed their cosmos classification is correct.
Chocolate cosmos is a perennial though it behaves like an annual in my garden. I’ve never managed to keep it going for more than one summer, let alone through a string of winter frosts. Never mind, as it’s easy to raise from seed and my November seedlings, though still small, were blooming by February. I’ve planted them in a pot so I don’t accidentally lose them when they die down.
HOT-COLOURED COSMOS
For late summer and autumn colour in a hot border, Cosmos sulphureus is all you need to sow at the feet of sunflowers, perennial helianthus, heleniums and tall rudbeckias. The bog standard species is bright orange but there are seed mixes to stretch the colour spectrum from lemon yellow to vivid orange-red.
‘Tango’ (Egmont Seeds and Yates Seeds) was the weakest germinator in my trial but (go figure!) went on to be the strongest and tallest of this group in my garden with – in my opinion – the best colour. ‘Tango’ has double blooms of intense orange-red that glow in the late afternoon sunlight. It also holds its blooms higher above the foliage for a naturalistic effect.
‘Cosmic Orange’ (Egmont Seeds) is better for bedding, with smaller plants smothered in semi-double, clear orange flowers, while the ‘Brightness Mix’ (Kings Seeds) adds shades of yellow as well as orange.
SAVING COSMOS SEED
Without continuous deadheading throughout the season, cosmos will soon set seed. Saving this is as simple as cutting off any spent blooms with ripe seeds and popping them in a paper bag to finish drying. Be aware that cosmos cross-pollinates readily so expect a lucky dip of petal shapes, colours, flower sizes and plant heights from home-saved seed.
Cosmos also happily self-sows and when the first of these bonus babies inevitably pop up in spring, usually in the middle of my gravel paths, it’s a timely reminder to sow more cosmos for the season ahead.
The Mexican native Cosmos sulphureus has marigold-like foliage topped with blazing orange and yellow daisies. It self-seeds readily, but never becomes a nuisance in New Zealand gardens.