Publications

The Garden
May 2003

Developing a hardy passion

To be launched at the Chelsea Flower Show, Passiflora ‘Eden’ is a hardy, purple, scented passionflower. Philip Clayton meets the breeder and discovers how this new plant was developed

Images: Hillier Nurseries / Larry Rynsard and David Murray

Passionflowers, among the most instantly recognisable of climbing plants, are widely renowned for their beautiful, distinctive blooms. Although there are 465 species of Passiflora worldwide - most of them from South America - few are hardy enough to overwinter outside in the UK.

Horticulturist Mark Bradbury from South London set out to change all this in the early 1990s. He wanted to produce a genuinely hardy passionflower which combined some of the excitement and sheer ‘flower power’ exhibited by many of the magnificent tender species, but which also included a strong degree of frost hardiness.

Breeding hardiness

In UK gardens, the Passiflora genus is most often represented by popular blue-flowered P. caerulea. Good selections of this can make fine, hardy garden plants, but seed-raised examples often produce poorly-coloured blooms and prove shy to flower. Passiflora caerulea ‘Constance Elliot’, with its subtle, ivory-coloured flowers, is also fairly hardy. Toughest of all, P. incarnata, known in the USA as ‘May Pops’, will tolerate -16°C (3°F). It dies to the ground, regenerating in spring from a fleshy rootstock, to produce flowers of a subtle pale pink.

In recent years, some hardy cultivars have been developed. Among these, purple-flowered ‘Incense’, bred in 1973 in Florida originally for fruit production, will tolerate -8°C (18°F), but all top growth dies below 0°C (32°F), making it less than ideal for cultivation in much of the UK. It also suffers from virus problems, although more recent ‘New Incense’ is virus free.

Cor Laurens, holder of the Dutch national passionflower collection, has bred passionflower hybrids of some hardiness including ‘Purple Haze’. The white-petalled flowers have long purple corona filaments (the crown of thread-like structures), a dark magenta centre and a delicate scent.

Mark had worked as a young man on a private estate under a head gardener who had, in turn, been employed by Lawrence Johnston at Hidcote in Gloucstershire. Mark developed an interest in horticulture, went on to study at Lackham and Pershore Colleges, and later became a parks officer.

Commercially minded

Apart from a stint working in the City in advertising, Mark has spent most of the last 18 years managing successful garden centres in the Home Counties. He is unashamedly commercially driven and feels that there is no room for sentimentality in commercial horticulture. ‘Many fine nurseries have gone out of business as they are unwilling, or unable, to adapt,’ he sighs.

Mark has developed his new passionflowers with such maxims in mind. In order to succeed, he feels any plant he breeds must be ‘long-lasting and adaptable to a range of conditions, and therefore able to perform in the average garden’. As a result, he looks for a wide range of attributes in his passionflowers. He selects for not only hardiness, but also flower size, amount of bloom, vigour, reduced foliage size and even scent, a feature found in some tender passionflower species.

But why specialise in passionflowers? Mark feels that while many gardeners admire these plants, people believe they are tropical and tricky to grow. ‘I want to broaden the range of plants available to UK growers, and within Passiflora there is so much potential’.

Mark has always enjoyed growing plants of borderline hardiness and pushing the limits at which they will survive. One way of doing this is to breed a degree of hardiness into otherwise tender plants.

Birth of ‘Eden’

Mark carries out his plant breeding on a surprisingly domestic scale - indeed the whole enterprise started as something of a hobby. He has found that because the plants are quick to develop, results of crosses can soon be assessed, and promising hybrids selected. Those which do not make the grade are discarded or given to friends.

Passiflora seed that is sown in September will produce flowers by the following summer if plants are forced. To do this, seedlings are treated ruthlessly; watering is only carried out sparingly which stresses the plant and ensures it produces flowers in order to set seed and reproduce.

This regime has the knock-on effect that plants do not produce masses of vegetation, which in turn cuts down on the amount of glasshouse and polytunnel space required.

It was in this way that Mark bred his first hardy passionflower cultivar, one which measures up to his exacting standards. It has been named Passiflora ‘Eden’, after the Eden Project in Cornwall, and has purple flowers, a trait inherited from its parent ‘Amethyst’, which are produced from June-October. Blooms can measure 11cm (4.5in) across (P. caerulea is typically 7cm/3in) once the plant becomes established. The flowers have a sweet, delicate scent and their blue corona filaments measure 7cm (3in) across.

Bred in 1994, ‘Eden’ has now been kept outdoors through six winters. It has tolerated with ease at least -7°C (19°F) - thanks to the other parent, P. caerulea - not even losing its attractive mauve-flushed three-lobed leaves. Over time, this vigorous cultivar can cover at least 10.5m (35ft) of vertical surface in a suitable sunny, sheltered, well-drained site.

This new cultivar has proved to be highly floriferous, having shorter internodes (the section of stem between each leaf) than P. caerulea, which results in more flowers appearing on each stem. This feature means that plants should be well suited to growing around a hoop as a house plant. It also impacts on the likely popularity of this passionflower at garden centres, as it should flower while still young and compact, unlike P. caerulea.

‘When I breed a plant I envisage how it will look in a pot, up a cane at the garden centre. I need to consider if people will be attracted to buy it,’ smiles Mark.

Chelsea debutante

He will not have to wait long to find out. Although ‘Eden’ has proved to be slower to root from cuttings than P. caerulea, it establishes quickly in a pot, and thousands have been propagated at the Hiller Nursery in Hampshire, ready to go on sale at garden centres after the plant’s public launch at the Chelsea Flower Show.

At the show Passiflora ‘Eden’ will feature in the Hillier ‘Dove Garden’ which will highlight the healing qualities of plants and gardens. Large columns of the passionflower will be included, and plants have been grown on under glass to ensure a spectacular crop of flowers is produced in time for the show.

So what next? Mark has other seedlings that he has high hopes for and, although like any good businessman he keeps his cards close to his chest, his enthusiasum shines through. He explains how he hopes to develop cultivars with better scent and even larger flowers, especially those that have blue or purple petals. Even more exciting, a chocolate-coloured selection is a distinct possibility. Flower shape is also an area for development, as some of the tender species have blooms with wildly contorted corona filaments. A hardy red-flowered hybrid is also on the wish list, and he is interested in developing plants that produce coloured or patterned foliage - an attractive feature of some passionflower species.

‘My aim is to make passionflowers as popular with gardeners as clematis,’ Mark grins. ‘The genetic diversity exists to produce some hugely exciting plants well suited for growing in the UK.’

Perhaps Passiflora ‘Eden’ is the start of a passionflower revolution. Mark Bradbury certainly hopes so.

Philip Clayton is Trainee Horticultural Journalist with The Garden

Plants of Passiflora ‘Eden’will be available at garden centres from May onwards, priced £11.99, and will be on display at the Chelsea Flower Show on stand FPC24 in the West Pavilion. The show takes place from 20-23 May. Tickets must be booked in advance, tel: 0870 906 3780.
Click here for our online coverage of Chelsea Flower Show 2003

back to The Garden contents page