Germinating Passiflora Seeds

Passiflora is a large genus of tropical scrambling or twining vines originating in South America, more commonly referred to as ‘Passion Flowers’. In temperate climates such as the UK, many gardeners will be familiar with the Blue Passionflower (Passiflora caerulea) – one of the hardier members of this family. However, there are hundreds of species, but of these only a handful are cold hardy – the rest require frost free conditions at the very least in order to thrive.

To the butterfly breeder, Passiflora is an important genus of tropical plants because they are the host plants for a number of the ‘longwing’ butterflies, in the family Heliconidae. Longwing butterflies are particularly suited for breeding in a tropical glasshouse because of the longevity of the adult butterflies. However, this will require you to grow some of the more exotic species of Passiflora, if you are looking to breed a variety of species. Purchasing exotic passion flowers as established plants can be a costly business: whilst many UK nurseries are now selling tropical species, the price tag can be anywhere in the range of £15-£30 a plant. Although this is definitely the easier option, by investing a little time and money, it is much cheaper to raise them from seed.

Zebra Longwing (Heliconius charitonia) laying eggs on Passiflora caerulea in my tropical greenhouse.

Zebra Longwing Heliconius charitonia laying eggs on Passiflora caerulea in my tropical greenhouse.

As with many tropical seeds, germination can be erratic unless the seeds are fresh, but there are some little tips that will increase your germination rate quite considerably! Firstly, I would strongly advise anybody who does not own an electric heated propagator to invest in one. There are a range of models available and prices vary depending on size and features, so it’s worth doing a bit of research and buying one that’s right for you. The main requirements will be that it can heat up to at least 30°C and having a thermostatic control is handy, although adds to the cost. A propagator is an absolute must if you intend on growing a range of tropical plants from seed.

Passion Flower seeds are usually black in colour, and somewhat flattened. They have a hard outer coating, and in some cases it can be beneficial to ‘scarify’ the casing in order to encourage germination. This can be achieved with some sandpaper by gently rubbing down the coating, allowing moisture to more easily penetrate the seed. After this, they should be soaked for approximately 24 hours in orange or pineapple juice. This may sound odd, but the acidity of the juice, again, helps to break down the hard outer coating of the seed. It is also beneficial to pour the juice in which they have been soaking over the seeds once they are sown. Although this may cause a mould to grow over the compost, this should not adversely affect germination of the seeds.

After 24 hours, the seeds can be sown. I usually sow them into washed, clean pots filled with ericaceous compost. It is not a necessity, but I have found more success with using slightly acidic compost. The depth at which the seeds should be planted varies from species to species, but I have found that a very light covering of compost and vermiculite is all that is required.

Finally, all that is left to do is give them a slight watering, and label each pot. They should be kept in the propagator at a temperature of around 25-30°C until they germinate. This can take anything from a couple of weeks to a couple of months. Sunlight is essential, so the propagator should also be kept on a sunny windowsill. Ensure that the compost is kept moist, but not wet.

Seeds can be sown at any time, although I tend to sow mine from late January into February, as the days begin to get longer, and to give the new plants plenty of growing time before winter. This year I am sowing the following species of Passiflora:

Winged Passion Flower Passiflora alata
A beautiful species with crimson petals and sepals, and thick, richly banded corona filaments.

Stinking Passion Flower Passiflora foetida
An unusual Passion Flower which is only used as larval host plant by a handful of butterflies.

Maypop Passiflora incarnata
Another hardy passion flower with edible fruits.

Vine-Leaved Passion Flower Passiflora vitifolia
Striking scarlet-red flowers and vine-like leaves.

I will keep you updated on the success of these as the year progresses. Depending on which species germinate (if any), will determine which species of butterfly I will be breeding in the greenhouse next year.

Irrespective of whether you are breeding butterflies or not – growing your own exotic passion flower from seed is certainly a rewarding effort. The flowers of Passiflora alata and Passiflora vitifolia are, in my opinion, a real joy to behold: even better if you can say the plant has been nurtured by you completely from seed to flower.

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