Pick of the zingiest zinnias and how to grow them as cut flowers
‘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,
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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.
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: doubleflowered 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 semidouble 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 Trial Field at Wisley
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!