Passiflora caerulea- Passion Flower

The Passiflora Caerulea is undoubtedly the hardiest of ornamental passion flowers. This vigorous South American species is also known as the blue passionflower, due to the bluish colour of its flowers which are curiously organised. Capable of covering entire walls and climbing trees, this vine-plant will be appreciated for its long flowering period with a sweet citrus fragrance, followed by pretty orange fruits that are edible but have no taste value. Impractical in hot climates, this passionflower will appeal more to gardeners who can appreciate its exotic charm without fearing being overwhelmed by its beautiful exuberance.

The Passiflora caerulea belongs to the family of Passifloraceae, which includes about 400 species of more or less evergreen ramblers, mostly native to tropical regions of South America. This botanical species is distinguished by its good resistance to frost (-12°C (10.4°F) for an adult specimen) and to summer drought. Not demanding in terms of soil, it can adapt to any well-drained and sufficiently deep soil, whether acidic, neutral or alkaline. Almost evergreen in hot climates will lose their foliage, and their stems may be frozen in winter in cooler areas. It can be grown in open ground there, provided it is exposed to the south or west and mulched in winter. Its robust stump will then produce new vigorous shoots in spring.

The long, flexible and angular stems of the blue passionflower can exceed 7 m (23ft) in length, its growth is very rapid in fertile and moist soil, and its rooting is deep. The green branches of this liana cling to any support by means of very strong tendrils and are adorned with wide leaves 6-8 cm (2-3in) thick, divided into 5 lobed palmates, dark green. Its slightly fragrant flowering is continuous, from June-July until the first frost. The large flowers measuring 8 cm (3in) in diameter are composed of 3 large oval bracts, pale green in colour, topped with 5 white-blue petals, themselves topped with a double crown of tricoloured filaments, bluish-violet on the periphery, white in the centre and purple at the base. In the centre of the flower, there is a column (the pistil) surrounded by 5 stamens ending in small 'hammers'. The fragrance of the flowers is tart and sweet, and they are highly visited by pollinating insects. Ovoid and soft fruits, the size of a small egg, orange in colour, follow the flowers. When raw and still green, the fruit, which contains cyanide acid, is toxic. Hidden under a thick skin are the seeds coated with a reddish pulp, which is not very juicy or tasty. Some birds consume them and thus contribute to the plant's dispersal in the garden.

Widely planted in old southern gardens, the blue passionflower is a vigorous rambler that needs to be controlled in hotter climates: its vigour is such that it becomes almost impossible to make it disappear once it is well established. However, severe pruning in early spring and regular removal of fruits can help limit its spread. This climbing plant, which grows without assistance and watering once established, works wonders on wire fences or when allowed to conquer an old tree. For example, combine it with a Chinese wisteria, a terniflora clematis, or a Polygonum aubertii: these are all equally vigorous climbers that keep it in check while extending the flowering period along a large fence grid.