Passion flower is named in reference to the Passion of Christ. The structure of the flowers struck early missionaries to the New World as being an ideal mnemonic for teaching the gospels of Christ.
The species I am interested in here is Passiflora incarnata, the maypop. None of the other species really have a chance of surviving this far north.
I’ve had some experience with passion flowers in the past. One of the keys is too keep the moisture on and the heat up.
CRFG mentions planting the seed 1/2 to 1 inch deep, and that stored seed has a lower, slower germination rate.
JLHudson’s catalog suggests a 2 month moist, cold pre-treatment for the seeds.
PFaF suggests soaking for 12 hours in water, then planting in a greenhouse in late winter or early spring.
Reich’s commentary on starting maypop is consistent with what I am familiar with. Warmer means faster sprouting. He suggests that at 90F you might wait only a week or two for seedlings. He goes a bit further and suggests that light inhibits germination, and thus he recommends the seeds be planted deeply. He also recommends soaking the seeds in water for a day before planting.
I put about 2 dozen seeds into a 1 gallon black plastic pot, 1″ or better down in the soil, in full sun. I think I’ll start the next batch this winter in the refrigerator.