Plant of the Month: May

Paeonias

by Peter Williams

To most people the paeony is ‘that’ plant with the enormous, dark red flowers that they first saw growing in their parent’s, or grandparent’s garden. That plant was almost certainly, the common paeony, Paeonia x festiva ‘Rubra Plena’.

Fig.1 Paeonia x festiva ‘Rubra Plena’ Image HPS library

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This lovely old cultivar has been a cottage garden favourite since at least the seventeenth century and has a cast-iron constitution. Provided it is surrounded by other plants to support its oversized flowers, it will exist without care or attention for decades. It is impeccably well behaved and will not leave its post or wander into the company of other plants without an introduction.

The wild and cultivated cousins of the old faithful ‘Rubra Plena’ represent some of the most beautiful hardy plants. For millennia, they have been celebrated in art and culture, and highly valued for their medicinal properties.

Paeonies continue to be important today as garden plants, sources of medicinal compounds, edible oils and as high-value cut flowers. Indeed, the paeony cut-flower business is now a global industry and before the current Corona pandemic, over 100 million cut paeony flowers were sold annually.

The importance of the paeony family is all the more remarkable because it is so very small. It contains just one genus with approximately 36 species.

Until fairly recently, paeonies were thought to be closely related to Glaucidium because of their superficial similarities. However, recent genetic analysis has shown that Paeoniaceae is a distinct family and Glaucidium is a genus in the family Ranunculaceae.

Fig. 2 Plants of similar appearance but members of different families

Paeonies occur naturally in northern temperate zones of Asia, Southern Europe and just two species are found in North America. Three groupings are currently recognised – The largest, the Paeoniae, includes most species of herbaceous paeonies; the Moutan division contains all the shrubby species and Onaepia is composed of the two north American herbaceous species, P. brownii and P.californica. This short article will concentrate upon the herbaceous paeonies from the Paeoniae section of the genus.

Paeonies interbreed easily and very many natural and man-made hybrids exist. Indeed, the RHS Plant Finder has over five hundred entries under Paeonia although the total number of registered cultivars (from all three divisions) is in excess of 3000.

Paeony breeding in Europe became very active from the mid-19th Century when a number of nurserymen, including Jacques Calot and Auguste Dessert in France and James Kelway in Britain, produced scores of stunning new cultivars by crossing the white Chinese species P. lactiflora and the red European species P. officinalis.

The hybrids that resulted generally possessed large, scented, double flowers that lasted longer than the single-flowered species. Early selections like P. lactiflora ‘Duchess de Nemours’ (Calot,1856) and P. lactiflora ‘ Festiva Maxima’ (Miellez, 1851) quickly became very desirable garden plants in the late 1800’s and still are today.

Fig. 3 Two old cultivars that are still popular today Image HPS library

In 1908 French breeder, Victor Lemoine (of lilac and philadelphus breeding fame) produced possibly the most successful paeony of all time, P. lactiflora ‘Sarah Bernhardt’. It was named after the famous actress of the day and cut flowers from this cultivar account for more than half of all cut peony flowers sold.

Fig. 4 The two Sarah Bernhardts

There is a fascinating account of the actress at the Shakespeare blog website

Paeony breeding continued actively throughout the last century in Europe and North America and many notable P. lactiflora cultivars were introduced. ’Jan van Leeuwen’ and ‘Krinkled White’ were bred between the two world wars and ‘Bowl of Beauty’ and ‘White Wings’ in 1949. All are still widely grown and have semi-double flowers that required little or no staking.

Fig. 5 Paeonia lactiflora ‘Bowl of Beauty’ Image HPS library

P. lactiflora ‘Jan van Leeuwen’ featured to stunning effect in Tom Stuart-Smith’s galvanised tank garden at Chelsea in 2008. It was almost the only plant in flower on the stand that celebrated form and foliage effects and nursery firms offering this old variety sold all their stocks on the first day of the show.

Fig.6 Paeony ‘Jan van Leeuwen’ at Mount St John Garden, Felixkirk. The garden was designed by Tom Stuart-Smith

North American paeony breeders have had many successes and large numbers of first-rate cultivars have emerged. The ‘Coral’ series, dating from the mid 1960’s, are the result of crossing the shrubby P. peregrina with P. lactiflora. ‘Coral Charm’ registered in 1964 has the most vibrant coral pink colouration and is very popular both as a garden plant and as a source of cut flowers.

Fig. 7 Paeonia lactiflora ‘Coral Charm’ Image HPS Library

Paeony growing and collecting becomes addictive for some Hardy Planters in much the same way as snowdrops are irresistible to galanthophiles. Individuals often start by growing popular cultivars and then their interests turn to the species and the collection enlarges.

One advantage of including paeony species in a collection is that they generally flower earlier than the hybrids and thus lengthen the flowering season. A number are widely grown including the compact and mound forming P. cambessedesii and P.tenuifolia with fiery red flowers and very finely divided foliage. 

Fig. 8 left, Paeonia cambessedesii and right, Paeonia tenuifolia both images HPS library

P. obovata and P. mascula are elegance personified and may start flowering in early April. Both are worthy additions to any collection. P. mascula the male paeony, was found growing on Steep Holme, the tiny island in the Bristol Channel in the early 1800’s. It was initially thought that it might be a native species but in reality, it was probably introduced for medicinal purposes by the monks of the religious community established on the island in the Thirteenth Century.

Fig. 9 left, Paeonia obovata and right, Paeonia mascula

But of all the species available to enthusiasts, one stands head and shoulders above the rest in terms of popularity. This is pure yellow form of P. mlokosewitschii that is generally known as Molly the Witch. This lovely paeony was initially considered to be a species in its own right but now it is thought to be a sub-species of P. daurica and has been renamed P. daurica subsp. mlokosewitschii. 

Fig. 10 Paeonia mlokosewitschii Molly the Witch

It is found naturally only in eastern Georgia, north-western Azerbaijan and adjacent Russia, and grows in deciduous forests. The red flowered P. daurica has a far wider distribution and hybridizes with the yellow form occur to give variable coloured offspring.

The flowers on P. mlokosewitschii and the other species rarely last for much more than a week and this is why some gardeners feel that they (and all the hybrid cultivars!) are not garden worthy subjects. Paeony enthusiasts clearly would not agree and value fleeting beauty over longevity in terms of the flowers and enjoy many features of the plants in addition to the open flowers. The fat buds that expand at ground level in early spring give rise to highly coloured shoots and neat disease-free foliage that often colours well in autumn.

Fig. 11 P. mlokosewitschii emerging in February and in bud, in early April

Flower buds are visible for weeks before they expand and open – expectant anticipation is part of the enjoyment of growing paeonies.

Fig. 12 P. mlokosewitschii flowers first opening late April
Fig. 13 P. mlokosewitschii in full flower on Mayday 2020

After the flowers fade the furry seed pods (follicles) develop and finally split to reveal the shiny black seeds surrounded by crimson unfertilised ovules.

Fig. 14 P. mlokosewitschii seed pods – mid-August

All paeonies enjoy a sunny aspect but will take some shading. Species like P. mlokosewitschii that originate from open woodland environments probably do best in light shade.

Paeonies are not particular about soil type provided it does not get waterlogged for extended periods. They can be moved far more easily than most traditional gardening authorities would suggest and whilst they will survive nutrient deficiency and neglect, they respond well to feeding. Helpfully, they are not grazed by rabbits or deer because they possess an armoury of toxic chemicals. It is these chemicals that form the active ingredients when paeonies are used in traditional herbal medicines and which are extracted for use in modern pharmaceuticals.

Paeonies also invest resources into the biological control of aphids and other insect pests. They do this by secreting drops of sugary solution on the surface of developing buds. Ants feed on the sugary liquid and in return, keep the buds free from potentially damaging insects.

Fig. 15 Sugary secretions on buds being used by ants

Named cultivars are propagated by division of dormant tubers and is a very straightforward procedure. Established roots are carefully lifted, washed and the thick tubers are severed with a sharp knife. Each root segment with an obvious bud should make a new plant.

Paeonies can also be raised from seed but when this is done the offspring will not of course, be identical to the parent because they have resulted from sexual reproduction. This is often apparent with seed raised P. mlokosewitschii which may have pink or reddish flowers whilst the seed parent’s flowers were clear yellow.

Raising from seed is a very rewarding but rather slow process. When the follicles split to reveal the seeds in late summer, the embryos within are often not mature and will need a few weeks to achieve maturity. When this has occurred the seeds still possess a double dormancy. A warm period is needed to overcome dormancy associated with the emergence of the radicle (root)and the epicotyl (shoot) will not develop until the radicle has reached a critical length and then becomes chilled.  In experiments with P. ludlowii, the radicle had to be at least 6 mm long before it became sensitive to the chilling needed to break hypocotyl dormancy. The low temperature needed for this to occur was 5 degrees C, or lower, for a period of approximately three weeks. In practice this means that seeds sown in autumn or the following spring after formation, do not appear to do anything during the first year. In fact, during this time the radicle will have emerged and when chilled in the second winter, the epicotyl dormancy is broken and the shoot appears. Seeds obtained from seed exchange schemes or bought commercially usually arrive in January. If sown on arrival, the first shoots will emerge above ground approximately 12-14 months later. This germination pattern is exactly what I have observed for a number of species over several seasons.

Fig. 16 Seeds sown February 2015, shoot emergence February2016. Image taken in mid-March

This year, however, I have been surprised to observe that about 20% of the seeds I sowed last autumn have developed shoots this spring.  The seeds were sown fresh from the plants as usual, but weather conditions in autumn must have allowed embryo maturity, radicle emergence and growth to the point where it was large enough to be sensitive to chilling in late winter or spring thus breaking the shoot dormancy. The complex germination requirements have obviously evolved to maximise the establishment of seedlings in the wild.  The best way to mimic these conditions in cultivation is to pot the seeds as soon as possible but leave somewhere where they will experience natural temperature fluctuations. I usually place my seed trays in a shaded and well-ventilated cold-frame.

Fig. 17 Paeony seedling. Image taken 30th April 2020

Seedlings should be potted up annually or planted out into a nursery bed, and they will begin to flower in their third year.

As I write this in mid-May, some of the early flowering species have finished and the large-flowered cultivars have buds showing colour.  The next few weeks will be paeony bliss.

Fig. 18 David Barnes wonderful Paeony-rich garden in Ilkley, June 2016

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