Passionflowers (Passiflora) are found wild in North and South America, the West Indies, the Galapagos Islands, Africa, Australia, the Philippines, Asia, and many islands in the Pacific Ocean, but many of these wild plants have been introduced from other countries. South America is the true home for 95 percent of all passionflowers, the remainder coming from Asia, Australia, and North America. There are now between 475 and 485 recognized species of Passiflora with 10 or 20 additional species awaiting publication.
In their natural habitat, passionflowers have to battle their way to the top of the forest canopy, or through small dense shrubs in more scrubby areas. Most climb with the aid of tendrils but there are exceptions which have lost these climbing aids and live as small trees or climbing shrubs. Although they originated in the tropics, many species of passionflowers are remarkably tolerant of subtropical and even temperate climates.
Passionflowers as Houseplants
Although it is easy to find advice about growing passionflowers in a conservatory or greenhouse, there is very little information available concerning the suitability of most species as houseplants, growing in the lower light levels of a normal well-lit window. Nevertheless, I have grown a number of species and hybrids indoors and none of them have shown themselves unsuitable. The fragrant species give an added bonus when flowering starts. Passiflora antioquiensis, P. mollissima, P. xallardii, P. ‘Amethyst’, P. caerulea, P. x belotii, P. coriacea, P. xviolacea, P. rubra, and many others are all suitable for growing in small pots as houseplants and will flower freely over a long season.
The type of pot used for passionflowers is of little importance; clay or plastic will both do admirably but clay pots will need more frequent watering. I prefer a soil-based potting mixture but a well-drained peat-based mixture does produce good results. Good drainage is imperative and this can be achieved by adding up to 50 percent extra sharp sand or grit to your normal potting mixture. If peat-based mixtures are allowed to become water-saturated for a period, this may significantly reduce the pH of the potting mixture, causing root death and the death of the vine. A good method of watering with most indoor plants is to let them become dryish without the plant wilting and then water thoroughly, rather than giving extra water to the plant each day.
One may be very tempted to repot a vigorous and healthy vine into a larger pot, especially when watering has become necessary more than once a day during hot sunny spells, but the more root room you give a plant, the larger it becomes, so stand the pot on a tray or saucer of wet sand and water the top of the plant and the sand at each watering.
Liquid feeding is particularly essential for plants in small pots. This should be started in the spring as new growth becomes established, increased during the summertime and stopped in late summer or early autumn. This allows the young stems to ripen and helps them overwinter. There are many excellent proprietary brands of liquid feed which are suitable for all passionflowers and should be used following the manufacturer’s instructions. Watering, too, should be decreased as winter approaches.
Exposure and Humidity
It is most important to find a well-lit window, if possible, south-facing. Spraying over the foliage with a spray gun or watering can during sunny spells, and occasionally during the winter, can be most beneficial and will increase the lifespan of individual leaves and encourage flowering. Young flower buds often abort on plants indoors or under glass and this is very often due to a very dry atmosphere, or to red spider mites which thrive in dry conditions. Spraying or misting the tops and undersides of the leaves will help to keep the vine healthy and keep this pest at bay. As I have already mentioned, most passionflowers come from humid parts of the world and this is why passionflowers, and many other plants, often grow best in your bathroom!
Keeping Your Plants in Bounds
If space is a limiting factor, careful and selective pruning is the answer. Many indoor vines are trained round and round a hoop or tripod and can reach lengths of 30 feet or more, so after a flowering period remove some very long growths which will have become naturally defoliated in the lower portion. It may be easier to unravel the whole plant and completely remove half to three-quarters of the long shoots with a knife or secateurs. These shoots should not be pruned flush with the main stem but removed leaving two inches of stem. Then rewind the remaining shoots back round their supports. The leaves will soon turn around to their proper orientation and when new shoots appear from the bases of the pruned stems and have made reasonable growth, the remaining old growth may be removed. In this way the size and general shape of the plant can be maintained.
It is important not to remove all the shoots and foliage in one operation as this will shock the vine, causing many fine fibrous roots to stop functioning and possibly die. This can encourage fungal attack to the roots and the possible death of the entire plant. Some species, such as P. racemosa, will not tolerate hard pruning (back to bare wood) as they are not able to produce growth buds from woody stems. Others, like P. rubra and P. morifolia, will grow back from a woody base, or from below soil level, like the herbaceous species P. incarnata and P. lutea. However, it is still not advisable to overprune plants growing indoors as they are always growing under less than ideal conditions. Passionflowers only flower on new growth, so the flowering potential of a vine is only slightly interrupted by pruning. The main disadvantage of all passionflowers is that the flowers only stay open for one or two days, and in hot weather slightly less. This drawback may well be overcome in the future when more plant breeders concentrate their efforts on improving not just the colors and vigor of hybrids but also the lasting qualities of the flowers. Who knows, we may have passionflowers that stay open all week!