Plant of the Month June 2018: Peonies

The peony is a flowering plant in the genus Paeonia, the only genus in the family Paeoniaceae. They are native to Asia, Europe and Western North America. They are amongst the most popular of all perennial plants, with their large blooms which are fragrant, and the added bonus of hardiness. Their flowering period is from early May to the end of June. I always think that they herald the start of summer. The stimulus for the emergence of new growth in February is the increase in day length, which is in contrast to irises which respond to increasing warmth.

Peonies are grown for their great range of colours and flower types, their fragrance, and relative freedom from pests and diseases. From the turn of the year, when the bronzy-red new shoots emerge in the company of snowdrops and winter aconites, through to the interesting seed pods and coloured leaves of autumn, peonies are indispensable in the garden.

They are named after Paeon, physician to the Greek gods. The old European species, P. officinalis, introduced here by the Romans, was used for its medicinal properties, which included a cure for jaundice, kidney pains, epilepsy, prevention of nightmares and the treatment of depression. In the 18th century, peony roots were recommended for weak hearts or stomachs.

Peonies have been grown in the UK since the fifteenth century and are a firm favourite in the English garden. P. officinalis and P. officinalis ‘Rubra Plena’ AGM, have been cottage garden favourites since the 17th century. Some will happily live for 60-100 years; each year getting stronger and flowering more profusely.

In the mid-19th century a trio of French nurserymen, Jacques Calot, Auguste Dessert and Felix Crousse, and an Englishman, James Kelway, started cross-breeding P. officinalis and the wild Chinese species, P. lactiflora, and created a whole new race of hybrids with big powder puff flowers. In 1856, Calot introduced P.lactiflora ‘Duchesse de Nemours’ AGM, a double peony with creamy white flowers which are sweetly scented.

Peony breeding was subsequently carried out by Kelways of Somerset between 1880 and 1920, and the nursery is still going strong today, and they exhibit at the RHS Chelsea Show. Click here for a link to their website.

They were followed by another Frenchman, Victor Lemoine, who in 1906 bred the famous pink double P. lactiflora ‘Sarah Bernhardt’ AGM. Today, the Dutch grow this in vast numbers for the cut-flower market.

Many peonies are fragrant; in some the scent is light, and in others the scent is only released after the flowers have been cut and placed in a vase. Scent also depends on the time of day, and a warm position. Good scented varieties include P. ‘Claire de Lune’ and P. lactiflora ‘Krinkled White’ .

P. lactiflora ‘Festiva Maxima’ AGM, which has white flowers with flecks of crimson near the centre, also has a good scent.

As interest in peonies grew, more wild species were introduced into English gardens. These include from the Caucasus, P. mlokosewitschii AGM, otherwise known as ‘Molly the Witch’. It has pale single lemon-sherbet coloured flowers over bronze-grey foliage.

It flowers early in late April, but not so early as P. tenuifolia, a beautiful species, also from the Caucasus, with fine thread-like foliage and blood red single flowers. P. ‘Early Windflower’, a cross between two species, (P. emodi x P. veitchii) emerges early, with intricately dissected foliage of deep, burnished bronze. It has single white blooms with a central boss of gold.

There are somewhere between 35 and 50 different species of peony belonging to the genus Paeonia. However, most of these botanical species grow wild in Asia, southern Europe, or western North America and very few are culivated and sold commercially; these include P. veitchii, P. mlokosewitschii, P.officinalis, and P. tenuifolia.

P. lactiflora is an herbaceous peony, which is native to central and eastern Asia and Northern China where it has been cultivated for about 1,600 years. There are at least 3,000 registered cultivars of P. lactiflora. Most of the peonies sold commercially are either cultivars of P. lactiflora, or else hybrids, with some of its genes. Historically, most varieties of peony sold were cultivars of P. lactiflora but often do not have strong enough stems to hold the large blossoms upright and need staking.

During the 1920’s Professor Saunders, working in New York, began crossing different species peonies which grow in the wild from the Mediterranean, up through Turkey, Iran into Russia and across from northern India into China and down into Japan. The flowers are almost always single.

The resulting hybrids carry the best characteristics of their wild relatives; they are hardy, early to flower and have beautiful foliage. The colour range of the flowers is broader than that of P. lactiflora, which is limited to white, red and pink. Hybrid peonies flowers can very dark red through to the palest pink and pure white, as well as soft creamy yellow through to coral and apricot. The leaves are often large, bright green and glossy.

The flowers are usually carried on strong thick stems, which means the blooms will not fall over, and do not require staking. P. lactiflora ‘Scarlet O’Hara’ has red single flowers, which last up to ten days. As the flowers age, the petals get bigger and fade to deep pink. P. lactiflora × officinalis ‘Red Charm’ has double red flowers that are long-lasting. The blooms form a domed ball of serrated petals within large guard petals and are held on stiff stems. P. ‘Avant Garde’ has single pink flowers.

Tree peonies (P. rockii) have woody stems that lose their leaves in autumn, but the woody stems stay intact.  They tend to bloom earlier and with larger flowers than the herbaceous peony. Tree peonies are long-lived, hardy deciduous shrubs provided they are grown in a suitable spot. P. delavayi var. delavayi f. lutea is a yellow tree peony.

Until recently the only peonies to produce yellow flowers were those of woody tree peonies, such as P. lutea, or the fleetingly beautiful herbaceous peony P. mlokosewitschii AGM. The successful crossing of tree and herbaceous peonies by a Japanese plant breeder, Mr Toichi Itoh, produced intersectional (Itoh) hybrids, truly yellow, double-flowered herbaceous peonies. He started work in 1948, and crossed the white herbaceous P.lactiflora ‘Kakoden’ and yellow hybrid tree peony, Paeonia x lemoinei. After thousands of crosses he raised just 36 yellow seedlings which bloomed in 1964, with double, yellow blooms. Dr Itoh never saw his achievement as be died in 1956. His hybrids were in danger of disappearing until Louis Smirnow introduced them into North America. In 1974 six were introduced with names like ‘Yellow Crown’ and ‘Yellow Emperor’.

Another well-known intersectional peony is P.‘Bartzella’. Intersectionals grow like herbaceous peonies, short and mounding, but they also have short woody, tree peony-like stems. These plants have the lovely leaf form of the tree peonies but die to the ground in the winter like herbaceous peonies. They are valued because they are available in colours that traditional peonies do not produce, in particular, more intense shades of yellow, peach, and coral such as P. ‘Copper Kettle’.

Of the different types of peonies, intersectional peonies have the best characteristics of all. The flowers and foliage are in perfect proportion to one another, taking the best from each of the parents, the tree (woody) and herbaceous peony. They bloom same time as herbaceous peonies from early to late June, but because they have so many buds they in bloom for longer, for up to 3 weeks or more. The flowers are big, and generally semi-double. The blooms are sterile, but the large furry empty seedpods, are very attractive. At night each flower closes up for protection helping it to last longer. A bloom can last as long as 5 days, with many lower side buds. Overall an intersectional peony can be in flower for up to 4 weeks, some 2 weeks longer than other types of peonies.

Peony flower forms are usually measured in rows of petals.

Single flowers have a single or possibly two rows of petals, often 5-12 petals total with a ring of golden stamens surrounding thick carpels. An example is P. cambessedesii AGM, also known as the Majorcan peony.

Semi-double flowers have three or more rows of petals, sometimes irregularly shaped petaloids/stamens mixed with petaloids, sometimes distinct stamen-and-carpel centre, such as the red P. lactiflora ‘Buckeye Belle’ an American hybrid, first bred in 1956 and currently a favourite with garden designers.

The ‘Lotus Form’ is a semi-double with curved, cupped petals creating a lotus-shaped bloom such as P. ‘Coral Charm’ AGM.

The Japanese Form’ is a semi-double have outer ‘guard’ petals but the majority of the stamens have been converted into narrow stamenoids which are petal-like. The stamen often retain their golden colour. The name of ‘Japanese’ is somewhat misleading as the varieties of this class are not necessarily of Japanese origin; but are admired by the Japanese.

An example of a Japanese peony is P. lactiflora ‘Lotus Queen’. with the stamens morphed into a large cluster of stamenoids, or very thin petals.

In the late 1940s, Dutch breeders introduced a peony that was half way between the double and the single, the so-called ‘anemone-flowered’ peony. In this, the stamens in the centre ruffle themselves up into semi-petals, often of a different colour to the surrounding proper petals. P. lactiflora ‘Bowl of Beauty’ AGM is one of the best of this kind, with bright pink petals curling round a froth of cream in the centre.

Double flowers have lots of petals and form a ‘powder-puff’ or domed crown. The ‘Rose Form’ is a double that opens on a flat plane like an old-fashioned rose, such as P. lactiflora ‘Festiva Maxima’ AGM.

The ‘bomb double’, is considered a type of double. Typically, the centre segments form a nice, round ball, sitting on top of a lower ring of ‘guard’ petals, which are sometimes of a different colour, (the word ‘bomb’ probably comes from ‘bombe’ which is the name of a round, frozen desert popular after World War I). P. lactiflora × officinalis ‘Red Charm’ is an example of this flower form. Doubles last longer in flower than singles but are more difficult to stake and keep the right way up in a rainstorm.

Peonies also provide colour in late summer and early autumn as the leaves start to turn colour. Usually by late August, they change from green to soft green and yellow, then red and finally shrivelling to brown. The widest range of autumn colours can be found on herbaceous peonies. The intersectional varieties (such as P. ‘Morning Lilac’) providing a strong, dignified show of orange, red, green and purple foliage whilst the remainder of the garden is in decline. After they have changed colour the foliage curls up and withers to a dull brown. They are a useful over wintering place for good insects such as ladybirds. However, this can make plants to susceptible to peony wilt.

Peonies will grow in most soils as long as they are not wet, including clay soils. They require a sunny or partially shaded site. Most herbaceous peonies grow to about 80-90cm tall and about 60-80cm wide. They take time to mature over 3-5 years.

Peonies are wildlife friendly and resistant to attack from slugs and snails, and rabbits. Ants are sometimes seen on the flower buds, but they are not harmful and disappear as the buds start to open.

Species herbaceous and tree peonies are self-fertile and, in the absence of other peony species, will produce seed true to type. They will, however, easily cross with other peonies and so unless the species is isolated, hybrids may well occur. Cultivars and hybrids, are usually sterile. Peony seeds need to be exposed to two chilling periods with a warm spell between them. The seeds are doubly dormant; this means the root emerges after the first chilling period but the stem and leaves only appear after the second winter. The seedlings can take up to five years to reach flowering size.

Propagation is by careful division of root stock in autumn. It is best to plant bare-rooted peonies with at least 3-5 ‘eyes’ or buds in autumn, planting them with the crown no more that 2.5-5cm below the surface. Most tree peonies especially named cultivars, are grafted on herbaceous peony rootstock. The graft union should be about 15cm below the soil level. Deep planting encourages the grafted plant to form its own roots, which reduces suckering from the herbaceous rootstock and prevents the rootstock becoming dominant.

Many peonies need staking in early spring before growth is too far advanced. Peonies will survive the harshest English winter (they are hardy to about -20C) and actually flower better following a cold winter.

The HPS publishes a booklet ‘Peonies’ by Gail Harland. Click here for link.

The National Collection of Paeonia (pre-1900 and early post-1900 P. lactiflora cvs.) is held by Mrs M Baber, c/o Plant Heritage, Gloucestershire.

Page image: Paeonia lactiflora ‘Bowl of Beauty’ AGM
(Image courtesy of HPS image library)

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