Passion Flower

Cultivation and Propagation

Passion flowers are in the main easy to grow, but they can be difficult to over winter because their roots are prone to rot if kept cold and wet. In the wild passion flowers grow where the ground is exceptionally well drained - slopes of the high Andes, the rain forest floor, even (as with P.Incarta and P.Lutea) in roadside rubble in quite arid areas. Therefore the ideal compost is a free draining, soil based mixture of equal parts sharp sand or gravel, medium or course peat and loam, rather than a peat based compost which can easily become waterlogged. By the same token, plants grown outdoors need well drained dryish soil which warms up quickly in spring.
Established plants have a better chance of over wintering than very young ones.
Many passion flowers can stand short periods of frost. If long periods are expected a little heat may be needed to prevent the roots being frozen. In the conservatory I find it is better, and less expensive, to put a little heat around the roots of tender plants than to raise the air temperature which only encourages the already stressed plant to attempt to photosynthesise, putting added strain on the root system and causing the leaves to dehydrate and wither. A single kilowatt (1,000 watt) electric heating cable buried in the growing bed or compost does does far more to protect plants than a 3 kilowatt fan heater left on for a similar period.
All passion flowers have comparatively small root systems and, unless a massive plant is required, grow to a fair size in a 25cm (10in) pot. Like many climbers passion flowers are greedy feeders when growing rapidly during the long summer days. Potting on as soon as necessary into a good well drained compost and regular feeding with high potash liquid fertiliser pays dividends.
Like me you may have experienced problems growing passion flowers from seed. At one time I held the opinion that passion flowers wouldn't grow from seed - it was just a story spread by some mischievous botanist! Like so many other tropical plants, passion flowers have not had to develop seed with keeping qualities as plants in temperate climates must do; there is no winter or dry season to overcome in the tropical rainforest. There are ways to improve the keeping qualities of passiflora seed but, in general, it is best to use fresh seed which germinates readily. Seed that has been stored for any length of time can take up to 12 months to germinate with less than 2 per cent chance of success.
To improve germination, lightly sandpaper the seeds on one or both sides using fine sandpaper, then soak them in tepid water for 24 hours. Sow 2-5mm deep in peat or soil based seed compost. Temperature is probably the most important factor in germination, ideally at 20 degrees C (68F) for 16 hours and 30 degrees C (86F) for 8 hours each day. If this is not possible, then a constant temperature of 26 degrees C (79F) is advisable. Using this technique fresh seed germinates in two to four weeks and older seed in four to eight weeks, but 12 to 48 weeks is not exceptional.
Having germinated your seed and over wintered your young plants, your next goal is to get them flowering. As we know only to well, many plants grown from seed can take years to flower. Passion flowers are no exception. Some species are said not to flower until they are 10 or 20 years old. I don't believe this, but have had some passion flowers that have not flowered for eight years. If you have grown P.caerulea from seed and found it reluctant to flower - sorry! Some seedlings never do.
There is a slight trace of hybridisation in the P. caerulea in our garden, which causes all seedlings to be variable. This variability can manifest itself in a reluctance to flower. If you raise passion flowers from seed, I suggest that you grow and plant out four to six plants and choose the best after flowering. You may be surprised how different they are.
Cuttings are easily rooted from all named hybrids and most species, and are best taken in early spring as the days are lengthening. The tip or end shoot is the best and easiest to take. With a sharp knife or secateurs cut closely below the node of the first or second mature leaf from the end shoot. Carefully remove the bottom leaf and all the tendrils and flower stalks. Dip the cut end of the stem in rooting powder and insert 1.5cm (1/2in) deep into compost - 15 cuttings will fit into a 12cm (5in) pot.
Nodal cuttings are useful when tip-cutting material is scarce. They should be 2 or 3 leaves long with the bottom leaf and tendril removed. The advantage here is that you can take numerous cuttings from one shoot.
A mixture of 50 per cent sharp sand and 50 per cent sphagnum moss peat is an ideal cutting compost, but just sharp sand, vermiculite, Perlite or peat will do. Don't use loam based compost for species from the subgenus Tasconia unless it is neutral or slightly acid.
Try to maintain soil temp of 18 - 21 C (65-70F). Cuttings will root at lower temperatures but may take a little longer. Many species and varieties will root on a warm windowsill, but it may be necessary to cover them with a clear polythene bag for the first week or so. Don't let the cuttings get to wet inside; either remove the bag for a while each day or make some small holes in it for ventilation.