Passiflora

Passionflowers can be propagated either genetically or vegetatively with few problems. In most cases they are grown from seeds or cuttings. They can also be propagated vegetatively by layering, root cuttings, air layering, or grafting, but because these procedures are quite intricate, they are recommended only for those species whose cuttings root with difficulty.

Young plants can be produced from store-bought seeds or from the seeds of fruit harvested from the garden. The seeds of most species need a soil temperature of at least 25°C in combination with a correspondingly high atmospheric or soil humidity. Sometimes even higher temperatures, such as 35°C, aid germination. While robust species such as Passiflora caerulea, P. capsularis, P. morifolia, P. ligularis, and P. edulis will germinate under less favorable conditions, growing more fastidious or tropical species from seeds will only be successful in a heated propagator or plastic-covered seed flat. To grow well and quickly, seedlings need at least 10 hours of daylight. When seeds are sown during winter, supplementary artificial light is necessary.

In most species, best results are achieved with dry fresh seeds. Older seeds may react unpredictably. Sometimes there is no difference to be noted in comparison with fresh seeds, but in most cases germination only occurs after some months, if at all. Seeds more than a few years old are rarely viable. However, agricultural experiments made in South America have revealed interesting results with Passiflora tripartita var. mollissima. While seeds several months old germinated only after a long time, if at all, the germination of seeds after a year's storage was rather good.

If the seeds are taken from a fruit, the arils must first be removed from the seeds — a rather tedious task. This can be achieved by rubbing the seeds in fine sand or washing them in a kitchen sieve. Under the moist, warm conditions in the propagator, mold may occur very rapidly, especially if small particles of pulp remain on the seeds. Some hobbyists dry the seeds on newspaper after washing; when completely dry, the seeds then separate easily from the remaining membranes. A preventive measure against mold is to treat seeds with a fungicide such as phthalimide or hydroxyquinoline sulfate, both tolerated well by plants. Dry seeds can be soaked overnight in plain water or tea. In some texts it is advised to soak seeds in milk or passionfruit juice. This does not make sense and is even detrimental. The juice of passionfruit contains exactly those inhibiting substances that prevent the seeds from germinating in the fruit.

The soil mix should be rather poor in nutrients and germ-free or sterilized. Proprietary seed-growing mixtures are best suited for this, as are small peat pots filled with a mixture of sand, peat, and standardized potting soil in equal parts. Instead of sand, use pumice gravel or perlite to make the soil more porous. Avoid using soil from the garden. This can be the breeding ground for noxious microorganisms or fungi, which will prosper under the warm conditions of a propagator and jeopardize the barely resistant seedlings.

Slightly cover the seeds with soil and firm them down a little. Depending on how old the seeds are, germination will occur after 10–28 days. In rare cases the first seedlings will appear only after some months. It is important to remain patient, even if no seedlings can be seen after 8 weeks. To prevent the dreaded toppling-over disease or damping-off, spray the seedlings regularly with a fungicide and regularly air out the propagator. As the young plants develop further, carefully harden them off by occasionally taking the lid off the propagator for an hour or longer.

The plants should remain in the propagator until they have reached a height of about 5 cm. After this point, move them into small pots, being careful not to damage the roots. Spray them with water several times a day initially to make the transition easier. The first flowers may appear within 6–9 months on species such as Passiflora capsularis, P. gracilis, and P. morifolia. As a rule, most passionflowers produce flowers the 2nd year after sowing. Sometimes, however, several years may pass before the first flowers appear, as is the case with P. serratodigitata and other species that flower in the canopy of their native forests. There are rare cases in which plants raised from seedlings have not flowered even after many years of cultivation, despite the best care. This does not occur with vegetative propagation by cuttings taken from flowering plants of the same species.