Zinnias in abundance in the Trial Fields at RHS Wisley.
Another over-bright afternoon – too sunny really to get the best out of these brightest of summer stars – but I was there and so were they, in great abundance too and stars many of them are, of the late summer border, still in the finest of fettles. Not all, mind you – Graham Rice writes about these trials in the article below from earlier this month – but many clearly are worth the effort –
Pick of the zingiest zinnias and how to grow them as cut flowers
These dazzling blooms make superb bouquets, boasting more colours than any other annualCredit: Clara Molden; GAP Photos/Howard Rice – Mr Fothergills Seeds Ltd
‘The popularity of zinnias grows with each successive season.” So said the great Roy Hay, founder of Britain in Bloom and instigator of the National Gardens Scheme, back in 1937. What happened?
Well, there seems to have been a divergence of opinion – Gertrude Jekyll wrote that the zinnia was “another fine annual that has been much spoilt by its would-be improvers”. But the “would-be improvers” carried on “improving” zinnias until in 1966 the RHS trial at Wisley had 75 varieties. There were 91 in the 2002 trial and this year 144 are growing in an impressive display at the RHS Garden at Wisley, marking the year of the zinnia.
Zinnias provide more different vibrant colours, on tall plants and short, than any other annual but enthusiasm for vivid colours has waxed and waned over the years. “Everyone loves a zinnia,” proclaims the latest catalogue from Thompson & Morgan – well, not really, because it was often thought that they were tricky to grow. And that has been true, especially since the Sixties, as it was then that peat-based seed compost was introduced.
Zinnias hate bad drainage and seedlings succumb to fungus infections if their roots stay wet. The new peat-based composts retained moisture better than the John Innes seed compost they replaced so it stayed damp for longer.
Zinnia roots are damaged and stems stressed in pricking out and, in the moist, peat-based composts, many simply collapsed and died. The advent of modules (trays of individual cells) in which one seed can be sown and the seedlings moved on into small pots without damage has made zinnias far easier to raise.
Modern hybrid varieties, known as Z. x marylandica, are also helpfully disease resistant. Those “would-be improvers” have been busy again.
Best varieties and how to grow them
There are about 18 species of zinnia, mainly annuals that grow in grassland and open scrub in Mexico.
The large-flowered types are derived from Z. elegans, which arrived in Britain in 1796. A huge range of vivid colours and intriguing flower forms has been developed from the murky purple wild species. Plants tend to be upright, boldly branched, with stout stems and glossy foliage that can be susceptible to disease.
While the many mixtures are certainly dazzling – often too dazzling – single colours are easier to use in the garden, and in a vase, to create harmonious arrangements; you can choose colours that fit your taste.
Choose the taller forms of Z. elegans to achieve long-season impact in a sunny border alongside dahlias, cannas, tithonia and castor oil plants
One problem with both single colours and mixtures is their unpredictability; looking over the Wisley display, I was again struck by this. Over the years, quality control by seed producers can slip: double-flowered varieties may include poorly formed single-flowered plants and plants in the wrong colours may appear.
‘Envy’ is a classic case of deterioration. It was a fine plant 20 years ago but in recent years I’ve noticed that the colour has been poor and many plants produce single instead of double flowers. I gave it up long ago. In the current Wisley display there are two examples of ‘Envy’, and in both the flowers are bathwater white.
I have tried the brand new ‘Queen Lime’ this year – it is uniformly double and a good, pure colour. Forget ‘Envy’, grow ‘Queen Lime’ instead. Others in the Queen Series are also excellent.
Coming down in scale, there are three types of smaller zinnias: Z. x marylandica, Aztec zinnias and dwarf forms of Z. elegans.
Many of the shorter, more spreading types fall under Z. x marylandica, a hybrid of Z. elegans and the dainty orange-flowered Z. angustifolia developed at the University of Maryland in the Eighties. Unlike Z. elegans, these hybrids are resistant to powdery mildew, alternaria blight and other diseases that plague more familiar zinnias.
Spreading and resilient, they carry huge numbers of smaller flowers, and if you need an annual that does the job of a French marigold but which is altogether more stylish look no further. All of the Profusion Series (mainly single) and Zahara Series (single and double) are good – or superb.
In the Zahara Series, fiery shades predominate, including the semi-double Zahara Sunburst, which has orange tips to every red petal, but also Zahara Starlight Rose, which has a raspberry streak on each white ray.
Shorter, smaller-flowered types derived from Z. haageana, in particular the Aztec Series, feature large numbers of small, tightly arranged double flowers in appealing colours and bicolours backed by slender foliage. These tend towards sunset and autumnal shades, with Aztec Gold and Aztec Orange being especially appealing. With their informal habit, they fit well at the front of mixed borders.
There are also a number of very short, squat forms of Z. elegans, including the Dreamland and Magellan Series with large flowers on small plants. They look as if they’ve had all their elegance sucked out of them. I don’t grow them at all.
In general, choose the taller forms of Z. elegans to achieve long-season impact in a sunny border alongside dahlias, cannas, tithonia and castor oil plants. Grow the shorter, spreading Z. x marylandica hybrids, especially the Zahara Series, in threes in 15-18in (38-45cm) terracotta pots or at the front of a sunny border in place of those dreaded marigolds.
The short and spreading Aztec Series can tumble out of large containers or make unusual summer ground cover. All make good cut flowers.
The 144 different zinnias growing on the Trials Field at Wisley are dazzling. The vibrancy of the colours is astonishing, and some of the fully double and crested flower forms are simply captivating. It is clear from the number of buds still to open that the display will continue for many weeks. The diligence of the trials staff in deadheading is a major factor in prolonging the display.
The Benary’s Giant Series look exceptional in the size of flowers, range and purity of colours, and reveal relatively few off-types. With 13 colours, the pick are ‘Benary’s Giant Salmon Rose’, ‘Benary’s Giant Lime’ and ‘Benary’s Deep Red’, but none is poor.
The hard-to-find ‘Miss Wilmott’ (rich rose pink) was also exceptional, as was ‘Purple Prince’, which is easier to find. But many of the fancy speckled and striped colours (‘Candy Cane’, ‘Pop Art’, Whirligig) included pretty individual plants but far too many off-types.
Sprite looks a fine smaller-flowered, double and semi-double mix for cutting, with colours including a lovely golden apricot.
I’ve been enthusing about the three in the Zinderella Series of crested types after growing them last year, but here they prove my point about inconsistency: too many individual plants are without the necessary crested flowers. At its best, ‘Zinderella Peach’ is one of the most lovely of all zinnias. At Wisley it is poor.
Among the dwarf types, the Dreamland and Magellan series are colourful but utterly without elegance, while seeing all the many colours of the Zahara and Profusion series reveals their consistently high quality. Such colour!
Plant Trials can be viewed on the Trials Field at RHS Wisley, Surrey – visit rhs.org.uk
While many plants are past their best and gardeners prepare for autumn, Sarah Raven offers a final burst of sunshine.
Pick a winner: get the colour combination right and mini zinnias in multicoloured glass vases, such as Zinnia ‘Sprite Mix’, ‘Zahara Fire’ and ‘Coral Rose’ help to prolong the summer Photo: Jonathan Buckley
By Sarah Raven
7:00AM BST 31 Aug 2013
The best zinnias I’ve ever seen were lining a path to a primary school in Sri Lanka. They were flowering in February in the fort town of Galle, on the south coast of the island, thriving in an environment of deluging, monsoon rain, interspersed with hot sun and high humidity. They loved it.
The plants, spaced 18in (46cm) apart, had merged into a hedge standing over 4ft (122cm) high and were massively flowery and luxuriant. I did a double take before realising they were just the common or garden zinnia, ‘Dahlia Mix’.
That hedge taught me what zinnias truly like – not always easy to provide in Britain, but still possible. This year, with four times the number of sunny, summer days in Sussex compared with last, zinnias look magnificent.
There’s no better late-summer plant, with a brilliant range of colours and flowers that look as though they’ve been cut from velvet-coated cardboard. Whenever I touch the petals, I’m straight back to Fuzzy Felt as a child. The texture is just the same.
So how do we get the best out of zinnias? One important thing to know about them is that, from the moment of germination right through their life cycle, they’re particularly prone to damping off and botrytis. In a damp, cool year, with high air humidity, plants can get a plateau of mould, which sits on the growth tip and rots down into the heart of the plant. For this reason, you’ll find that lots of zinnia seeds are sold ready-coated with fungicide.
A bunch of ‘Benary’s Giant Lime’, ‘Giant White’ and ‘Oklahoma Ivory’ (JONATHAN BUCKLEY)
Zinnias famously hate root disturbance, so it is best to sow directly into freely drained soil with a fine tilth. Sow two or three seeds 2in (5cm) apart at 12in (30cm) spacing. Thin out the seedlings, so you end up with one plant every 12in (30cm) or so. You can also sow into modules (I use coir Jiffy’s), so there’s no pricking out, and plant out when still small with only a pair or two of true leaves. That way you minimise root handling.
Don’t sow too early. Remember the heat of Sri Lanka where they fare so well, and wait until the nights are warm enough to eat outside.
If the evening temperatures are chilly enough to have you reaching for the blankets to eat supper in the garden, then it’s still too cold. If you live in a part of the country where supper outside is a once-every-five-years experience, then sadly zinnias are not for you, although you could try growing them in a greenhouse or polytunnel.
Plants are best supported by individual stakes or, if being grown in a veg or cutting garden for picking, they look fine pushing up through nylon clematis or wire sheep netting, stretched horizontally one foot (30cm) or so off the ground and tied taut onto a series of canes. Even if your plants are not going to reach Sri Lankan heights, they benefit greatly from growing straight early on. If they collapse over, they’ll never grow or flower as well as when vertically supported.
The other key fact I learnt in Sri Lanka was that, as well as plenty of sun and heat, zinnias love a good amount of water, and this summer I’ve lavished mine with a good dousing every week at their roots – how they’ve loved it. Warm, moist soil and warm, moist air is what you’re looking for, and if we don’t get it naturally, that’s what you’re aiming to fake.
A cut above the rest
As cut flowers, zinnias are hard to beat, and in a cut-flower trial I visited recently at The National Cut Flower Centre near Spalding, Lincolnshire, the Benary’s range (so-called after the German plant breeder) were reigning supreme.
‘Oriole’ with green nicotiana (JONATHAN BUCKLEY)
With this selection, the necks are strong. Zinnias have hollow stems below the flower, so weak necks, which bruise and break off all too easily as you arrange them, can be a problem. This can make zinnias tricky to lace into a hand-tied bunch and is one of the reasons you often see them arranged just on their own.
With most zinnias, you’ll get at least a week in a vase if they’re kept cool. They last best on a short stem, with one flower arranged in a single-stem vase, or poked through a wooden grid to support the flowers just out of the water. The smaller-flowered forms such as ‘Sprite Mix’ and ‘Zahara Fire’ – which, as its name implies, opens red and gradually changes to orange – are the best for arranging on this scale and, cut short, have a vase life of about 10 days.
Scatter the flowers into similar coloured vases. Coloured glass is a good match to the zinnia look and feel, and they also suit bright ceramic jugs of red, turquoise or acid-green.
Most important, especially when you’re arranging, is to restrict the colour range. The green forms, such as ‘Envy’ or larger-flowered ‘Benary’s Giant Lime’ go with everything, but this is the only shade that does. Stick all the saturated, stained-glass colours together (either in the garden or picked to make a bunch), but keep these well away from the pales. Shoved in close together willy-nilly, zinnias can all too easily end up looking like dolly mixtures and lose their way on style.
A splash of colour: a bunch of ‘Benary’s Giant Purple’, ‘Giant Wine’ and ‘Giant Coral’ (JONATHAN BUCKLEY)
A cream variety such as ‘Oklahoma Ivory’ is beautiful mixed with the green (‘Benary’s Giant Lime’) and a white (‘Benary’s Giant White’), but the pales look all wrong mixed with dark reds and oranges. Similarly, the red and purple tones (‘Benary’s Giant Purple’ and ‘Benary’s Giant Wine’) are lovely with the contrast of a splash of rich vermilion-orange (‘Benary’s Giant Coral’), magnificent against petrol blue or rich, dark green; and the rich pinks (such as ‘Oriola’ or ‘Benary’s Giant Pink’) are marvellous with any of the reds and oranges, calmed down by ‘Envy’ green.
With your colours carefully chosen, zinnias will give you the best ever September bunch of flowers.
A little summer colour to finish off – and a small trial of Eucomis.
Martin Ogden - gardener and photographer, rose-whisperer and garden wanderer. Loving all things horticultural and learning every day. On the cusp of new adventures in Dorset...
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One thought on “A gazillion Zinnias – the Trial Fields at RHS Wisley”
I have also noticed a deterioration within some zinnias varieties. Many years ago, when the ‘Sun’ series had first been introduced, the flowers had been of excellent high quality, very full and beautiful, quite outstanding! Though, in recent years, they had proven much inferior with several plants producing poorly formed semi doubles.
The ‘Magellan’ series is excellent, especially the ‘Cherry’ and ‘Orange’. ‘Dreamland’ series is similar, though growth is more compact and plants bloom more abundantly, oh and the colors are stunning, it’s my top favorite!
The Teddington Gardener 
I have also noticed a deterioration within some zinnias varieties. Many years ago, when the ‘Sun’ series had first been introduced, the flowers had been of excellent high quality, very full and beautiful, quite outstanding! Though, in recent years, they had proven much inferior with several plants producing poorly formed semi doubles.
The ‘Magellan’ series is excellent, especially the ‘Cherry’ and ‘Orange’. ‘Dreamland’ series is similar, though growth is more compact and plants bloom more abundantly, oh and the colors are stunning, it’s my top favorite!