Pretty little things: How the double primrose continues to hold us in its thrall

Double flowers are bad news for the survival of the species. Most of them are sterile, because their stamens have foolishly been turned into extra petals. Nevertheless, they turn up from time to time among the wild populations of many plants.

If you think that a gorgeous Hybrid Tea or a perfect carnation is the last word in elegance, it is because one of its wild ancestors had a few extra petals, then our own ancestors thought it was pretty or useful and decided to preserve it. The rest is down to generations of industrious plant-breeders scratching around for a few grains of pollen to develop yet better plants for our enjoyment.

Double primroses are a case in point. Gerard’s Herball (1597) mentions several aberrant primulas, including a double-flowered cowslip ‘so commonly knowne that it needeth no description’ and ‘our garden double Prim-rose’, which he considered the ‘greatest beauty’ of all. John Parkinson, writing some 30 years later, says that ‘there are many prettie varieties’, including ‘the field Primrose, very thicke and double, and of the same sweete sent [sic] as the singles’.

One reason for the popularity of double primroses is that they are old-fashioned garden plants; their charm evokes the cottage gardens of olde England. All these double-flowered primulas arose as genetic mutations and quickly became popular plants among discriminating collectors. Double reds turned up later in the 17th century and, by 1800, several double purples and mauves were known. William Robinson wrote in 1883 that ‘no sweeter or prettier flowers ever warmed into beauty under a northern sun than their richly and delicately-tinted little rosettes’.

Perhaps the best known of Victorian doubles was ‘Marie Crousse’, still occasionally seen today, which is bright cerise with a few white flecks in its petals. Towards the end of the 19th century, the Aberdeen nurserymen James Cocker & Son began to breed double-flowered polyanthus — polyanthus is the name given to hybrids between cowslips and primroses. Cocker’s introductions carried the logo ‘Bon Accord’, which is the motto of the family’s native city. The Cockers were able to breed and name about 100 new cultivars, but few have survived through to modern times. They tend to have rather a short central stem, which means that a plant in flower often resembles a primrose more than a polyanthus.

The problem of breeding double primroses was made easier by the rediscovery in 1900 of Mendel’s experiments in plant hybridisation. At some point, scientists realised that a recessive gene was responsible for the production of double flowers. The only way to make progress was to cross two plants that were known to carry this gene. One quarter of the resultant seedlings would be double-flowered and two-thirds of the remaining plants would also have the potential to breed double-flowered seedlings, but obscured by the dominant gene for single flowers. That discovery has been the basis of all subsequent development or almost all, because some double primroses carry fewer petals in the autumn and may occasionally produce pollen and be capable of setting seed.

Crucial to the establishment of modern double primroses has been the work of a nursery called Barnhaven, which was founded in Oregon, USA, nearly 100 years ago, then moved first to the Lake District and finally to Brittany in France. Barnhaven is the leading breeder of specialist primroses and polyanthus, including hose-in-hose cultivars, jack-in-the greens, gold-laced cowslips — and doubles. It has succeeded in identifying a wide range of single-flowered varieties that carry the ‘double gene’. These are hand-pollinated and their seed is sold with the warning that only a quarter of the seedlings are likely to be doubles. Nevertheless, the range of the nursery’s colours is remarkable and many amateurs speak enthusiastically of its seedlings.

There was a revival of interest in double primroses in the 1970s and 1980s, but only a few new cultivars were introduced. Commercial growers found them too labour-intensive in terms of feeding, watering and dividing. Enthusiasts scour the lists of traditional nurserymen and pounce on anything they can find. A few are listed in the RHS Plant Finder: look out for pinky-orange-yellow ‘Ken Dearman’, violet-blue ‘Blue Sapphire’, rich-red ‘Corporal Baxter’ and the spectacular ‘Miss Indigo’, a Barnhaven seedling with dark-blue flowers that have irregular white edges.

Nowadays, double primroses are micropropagated — these are the ones you see in garden centres, marketed as smart bedding plants. The leading introducer of new doubles is David Kerley, a professional plant breeder from Cambridgeshire. He is highly regarded for the garden-worthiness of his plants — he trials them very carefully — and also for the introduction of new colours and combinations. Kerley’s primroses carry his Belarina trademark, followed by their colour. Belarina Pink Champagne and Belarina Tangerine Twist are among his best known, but many varieties — there are more than a dozen in commerce now — are bicolored, with a delicious combination of shades in every petal.

Most of the double primulas grown today are sophisticated forms of our common primrose, but a few are more closely related to cowslips. ‘Katy McSparron’ is said to be a cross between a cowslip and a polyantha, but most people consider it merely a double cowslip. It is packed with petals and easy to grow — and the flowers have a good cowslip scent, too. There is also an excellent double-flowered form of the old gold-laced cowslip called ‘Elizabeth Killelay’. It is not thickly double — if you peer into the flowers, you can see the mahogany-coloured petals also have a yellow base — but the golden edging is a wonderful contrast for the dark rows of outer petals.

Despite their exquisite shapes and colours, there is as yet only one National Collection of double primroses. It stretches to some 90 different cultivars, curated by Caroline Stone at her Glebe Garden in north Cornwall since 2014. She is an avid researcher and enthusiastic collector, determined to hunt down and conserve every double primrose that might otherwise be lost to cultivation. She worries that many modern varieties have already disappeared from sight: ‘Torchlight’, for example, was introduced by Hopleys of Much Hadham in Hertfordshire in about 1980 and even given an RHS Award of Garden Merit, but nonetheless seems to be extinct.

She also has successes: Parkinson’s original ‘field Primrose, very thicke and double’ no longer exists, but Stone has no fewer than five double forms of our native wild primrose, each of which has a different arrangement of its petals. Double primroses should be as easy to grow as any other primrose or polyantha. At the end of the 19th century, William Robinson recommended them for mossy banks, alongside uncomplicated shade-lovers such as dog’s-tooth violets, lily-of-the-valley and cyclamen, but anywhere where they are protected from the full-on heat and drought of summer is usually acceptable.

All double primroses, cowslips and polyanthus benefit from regular lifting, division and replanting in fresh soil to maintain their vigour. Some need splitting more frequently than others. The general rule is to split the clumps once a year, a job best done in autumn when there is plenty of rain and the soil is still warm enough to encourage the plant to root well. Some nurserymen who want to build up stocks for sale split them up immediately after flowering and then again in autumn.

All gardeners, however, find that some are easier to cultivate than others. The paradox is that the ‘difficult’ ones that malinger must once have been vigorous enough to be propagated in the first place.