Passiflora have the reputation of being difficult to propagate by seed.
You may have tried to sow Passiflora and thrown away the lot after a few months.
But Passiflora are not exactly difficult to sow, it’s rather that germination time varies considerably and sometimes it takes months.
At best, Passiflora germinates in 2-4 weeks but it takes 6 months or more.
It is useful to know a few things so that may you succeed on your next attempt.
Freshness of the seeds:
Most Passiflora germinate soon after maturity of the fruit: within 1 month. After that, the germination time may extend to several months.
From 12 months after the harvest, germination rate is greatly reduced and only about 2-5% of the seeds will sprout.
If you harvest seeds, it is best to sow immediately. That is when germination rate is highest and germination time shortest.
Soaking the seeds:
You have probably read on the internet that soaking the seeds promotes the germination of Passiflora seeds:
- in Passion fruit juice: most fruits contain substances that inhibit germination. Unless you leave the fruit to rot, soaking the seeds in Passion fruit juice does not help at all.
- in orange juice: same as in Passion fruit juice, no effect whatsoever
- in water: as long as the hard seed coat is not damaged, water can not penetrate to the embryo. And this regardless of the duration of the soaking or the temperature of the water.
Soaking the seeds only makes sense when the seed coat has been previously damaged.
The seed coat of Passiflora is usually very hard. That’s the brown hard shell that surrounds the embryo.
Scarification is the damaging of the seed coat and this promotes germination: water can penetrate the hard seed coat to get to the embryo and this starts the germination process.
This happens naturally through microbiological activity when the flesh rots and can be done artificially, either chemically or mechanically.
Chemical scarification in labs with ethyl alcohol or sulfuric achieved varied results and is therefore not really recommended.
To scarify Passiflora seeds, it is recommended to:
- grind the seeds with fine sandpaper
- put the seeds in a jar filled with sand and shake the jar so the sand particles scratch the seed coat
Soaking after scarification:
After scarification, soak the seeds for 24h in water at room temperature.
The temperature of the water has hardly any significance, there was no significant difference in laboratory between soaking after scarification with water at room temperature, lukewarm (50 °C) or warm (80 °C) water.
Contrary to many other seeds, Passiflora seeds do not benefit from sterilization before sowing: sterilizing kills the micro-organisms and without microbial activity, the seed coats remains intact.
Sterilization of Passiflora seeds only makes sense if you want to sow in vitro on agar agar in sterile conditions. But in this case, the seed coat must be removed completely with a micro-vice.
In vitro sowing after complete removal of the seed coat is actually the procedure with the highest germination rate: 100% of the seeds germinate.
Most Passiflora species are tropical or subtropical and soil or bottom heating promotes germination.
If you do not provide soil heating, the seeds will germinate, but much slower.
Alternating the temperature also promotes the germination: 20/30 °C in cycles of 12 hours is better than constant 25-30 °C.
So provide soil heating but switch it off at night.
Once sown, the substrate must remain moist.
The easiest way to keep a good humidity level, is to sow a ziplock bag or plastic container with a lid.
Otherwise, as the water evaporates and you need to water again and again, there is a risk that you occasionally forget to check and your seeds will dry out.
Once the germination process has begun, it is important that the seeds have water, otherwise they dry out and die.
- use preferably fresh seeds
- scarify the seeds with sandpaper or sand
- soak the seeds in water at room temperature for 24h
- plant in potting soil, a 1 cm depth
- provide soil heating and switch the heating off at night so that the temperature fluctuates
- keep the substrate moist
- do not discard the seeds if they have not germinated after a few months, it can take more than 6 months
- Passiflora seedlings: Forest & Kim Starr