Plant a passion fruit vine
Add a touch of the exotic to your garden or greenhouse with a passion fruit vine; the exquisite, multi-coloured flowers are followed by heavy crops of sweet, succulent, aromatic fruit.
Although there are more than 300 species of passionflowers, most of them require tropical or sub-tropical growing conditions and are far too tender to be attempted in cool temperate climates. The variety most often grown in such conditions, either outdoors against a warm wall or in a greenhouse, is Passiflora caerulea. It is grown mainly for its striking blue, mauve, and greenish white flowers, rather than for the egg-shaped, rather bland fruit which appear towards the end of late summer.
There are, however, other varieties, less well known than P. caerulea, which are cultivated commercially for their sweet-sour fruit, and these also can be grown in a temperate climate, either in a conservatory, or outdoors in favoured sites withand winter protection. The Purple Granadilla (P. edulis) has less attractive flowers than P. caerulea, but its fruit is considered far superior.
The Giant Granadilla (P. quadrangularis), with its fantastic red, violet and white flowers, is the least hardy of the three, and must be grown indoors. Its fruit are very large, and it is well worth growing for the flowers alone.
The name ‘Passion flower’ was given to the plant by the Spanish missionaries who first came across it in Brazil; within the complicated structure of the flower, they saw various symbols of the Passion of Christ.
Passionflowers are climbing, woody, perennial plants, either semi-evergreen or deciduous, depending on species and growing conditions. They can reach a height of 10 m (30’) or more, and once a plant is growing well, the problem becomes one of controlling its exuberent growth, rather than nursing it along.
Cultivated outdoors is fairly straight forward, provided you bear in mind the sub-tropical origin of the plants. South or west facing walls supplied with a system of wires, are best, or freestanding pergolas can be used as supports in very sunny sheltered situations. Cold, shady, exposed gardens or frost pockets should be avoided. A border against a warm wall is an ideal planting site.
Although quite tolerant of most soils, heavy or waterlogged ones will either severely stunt passion fruits or else kill them outright. If theis a very dry one, dig in plenty of well-rotted manure or garden before planting, to improve moisture retention. Plant mid-spring through early autumn but pay particular attention to watering if you plant in hot weather.
In cold winters, the plants will almost certainly suffer some die-back due to frost damage, and may even be cut back to ground level. However, unless the winter has been exceptionally harsh, new shoots will spring from the base the following spring. You can protect them against winter weather by packing dry bracken, clean leaf litter or compost around and over the crown and the base of the stems. Alternatively, use black polythene (supported by vertical bam- boo canes stuck well into the ground) to cover the base of the stem. Once the vine is fully grown, it is obvious that, short of a major expenditure of effort and money, the plant will have to fend for itself.
Because of this susceptibility to frost damage, always wait until late spring or early summer before pruning.
You will then be able to cut out all the obviously dead shoots which will be brown instead of green, before attempting to prune the living growth. If the vine has come through the winter unscathed, and needs heavy pruning, thin it out, right down to ground level, and then cut back sideshoots on the remaining main stems to 15 cm (6”). This spur pruning may take a bit of time and patience, as a strong growing passiflora will be a mass of jumbled-up stems, tendrils and shoots, with no apparent beginning or end.
Although feeding is not strictly necessary, an annual top dressing of well-rotted manure in spring is appreciated, and a potash dressing in mid-summer, such as bonfire ash, at 120 g per sq m (4 oz per sq yd) or sulphate of potash at 7-15 g per sq m (¼ – ½ oz per sq yd) will help fruit to mature and improve the flavour. In. hot weather, water thoroughly and frequently; ideally, you should syringe the undersides of the foliage at the same time.
Passionflowers planted in a border will flower and fruit better if their roots are restricted, so try the effect of sinking a large wooden box into the border, and planting in that, or pushing corrugated iron sheets, cut to give a container shape about 90 x 45 cm (3 x 1-½), into the soil to a depth of about 31 cm (15”).
Indoors, you can grow passion fruit in a conservatory, or a warm or cool greenhouse, depending on the species. The most tender species, such as P. quadrangularis, need a minimum winter temperature of 13°C (55°F), while in spring and summer, the temperature should not fall below 18°C (65°F). In very hot weather, it is a good idea to shade the plant, either by whitewashing the greenhouse glass, or putting up a temporary muslin screen.
In the cool greenhouse, the temperature in winter can fall as low as 7°C (45°F); as long as the frost is kept out, varieties such as P. edulis will survive. Unless you already have a heated greenhouse, or are prepared to spend a great deal of money for fuel, it is better to select a variety suitable for the cool greenhouse.
Ideally, plant greenhouse passion fruit in late winter or early spring, although, if the plants are container grown, with care you can put them in any time of the year. Until they are established, keep them shaded from direct sunlight and also keep the air fairly moist, but be careful not to overwater. Once established, they prefer a dry atmosphere to a moist one.
The tendrils will need something around which to twine, so either provide vertical wires going up to the roof, or, if grown in a lean-to, provide parallel horizontal wires fixed to the wall with vine eyes. You may find that a vigorously growing vine will obscure most of the light, creating a grotto-like effect in your greenhouse. If this is the case, cut it back ruthlessly; shortening strong-growing canes by half is not excessive. Do this pruning in late winter or early spring, before the plants have begun vigorous new growth. Because fruit is only produced on new shoots, a pruning system based on gradually replacing old, non-productive wood is necessary if the vine is to crop at all well.
With outdoor-grown vines, pollination is normally done by insects; all passion fruit grown under glass should be hand pollinated with a camel hair brush, unless the weather is sufficiently warm to leave the greenhouse doors and the majority of the ventilators open.
Indoors or out, passion fruit make excellent subjects for container growing; the root confinement seems to actually encourage more prolific flowering and fruiting. They look particularly attractive in terracotta pots, and make an attractive feature on sheltered balconies or in paved courtyards. If you have grown your own plant from seeds, and it is in 7.5 cm (3”) pot, gradually repot it into larger and larger containers until it is in a 60 cm (2’) diameter pot. By then it will be an enormous plant, and will survive for many years, provided you remember to water it regularly. It is also a good idea to scrape away the top 2.5 cm (1”) of topsoil gently every spring and replace it with fresh compost. Whatever size pot you use, the growing compost should either be a good proprietary compost or else, if you wish to mix your own, use two parts by volume good loam to one part peat and one part leaf mould. Sprinkle in a little silver sand as well to improve drainage, and remember to put a good layer of broken bricks, crocks or gravel in the bottom of the pot before adding the compost.
As a rule, passion fruit is ready for picking about three months after the flowers have set. Because flowering can continue over two months or more in a warm summer or heated greenhouse, the period of fruiting will also be extended, rather than occuring as a glut. Remember, though, that once weather turns chilly in autumn, unripe fruits are not likely to ripen fully.
Passion fruit is actually at its best when over-ripe, with a -1/2ery wrinkled skin like a dried prune. Although it is not visually attractive and it appears old and leathery, the taste is sweetest and the aroma most pungent at this stage. The colour of the skin and flesh, the size and the shape vary according to the variety, but they all have relatively hard skin, and juicy pulp which is densely packed with edible seeds.
Fruit of the Purple Grenadilla (P. edulis) has, as its name suggests, purple skin, with an orange coloured flesh; they are round to egg-shaped and can weigh up to 60 g (2 oz) each. There is a variety called ‘Yellow Grenadilla’ (P. edulis flavicarpa) which is a yellow-skinned form.
The Giant Grenadilla (P. quadrangularis) has the largest fruit of the commonly cultivated varieties; they can reach up to 15 cm (6”) in length. The skin is greenish yellow in colour, and the fruits look like small. They have hollow cores, around which is purple, pungent, and heavily-seeded pulp.
The fruit of the common passion flower (P. caeridea) is edible, but not really as tasty as any of the above varieties. Its one good point is that it is the hardiest of all passion flowers, and the one most likely to survive the winters of the cool temperate climate.
The only serious trouble you are likely to encounter in temperate climates, is cucumber mosiac virus, which is, unfortunately easily spread by greenfly. The main symptoms are crinkled, mottled and distorted leaves, sometimes flecked yellow or pale yellow green. Occasionally the symptoms disappear during summer, only to reappear the following spring. There is no cure. If the infection is severe, destroy the plant.
The ripe fruit is used in a variety of ways. It can be served fresh with sugar and cream, or, alternatively, you can slice a small portion off the top of the fruit, scoop out some of the central flesh, and fill it with fruit liqueur or sherry.
Because the skin has a high pectin content, it is very useful for setting jams and jellies, either on its own or mixed with other fruit, while the sweet-sour flavour makes passion fruit a welcome addition to cakes and pastries. In tropical and sub-tropical countries, juice made from the pulp, with the seeds strained out, is a very popular drink.