Passion vines sprout readily from seed and grow rapidly into care-free plants almost anywhere that remains frost-free in USDA Planting Zones 6 to 9. You can purchase seeds, but it's not the best option because they'll probably be old. The seeds of the tropical Passiflora edulis Sims should be planted as soon after collection as possible for best results. The older the seeds are, the longer it will take for them to sprout. They lose their viability rapidly, and probably won't germinate at all after a year. Fortunately, fresh seeds are readily available, conveniently housed in the delicious passion fruits retailed by most grocery produce departments.
Place a fresh whole passion fruit out to finish ripening at room temperature. Select a spot free of direct sunlight where it will be out of your way until the skin starts shriveling. Don't worry about the quality of the fruit deteriorating during this time. Passion fruits are at their sweetest and tastiest when allowed to mature until the skin has shriveled.
Cut the fruit in half with a clean, sharp knife and scoop the gelatinous pulp containing the seeds out into a bowl with a spoon. Allow the bowl of pulp and seeds to sit out at room temperature for two or three days to age and ferment. This seems to accelerate seed germination, although the reason is unknown.
Cut the top off of an empty Styrofoam egg carton to create a seed-starting flat. Use a toothpick to poke 3 or 4 holes in the bottom of each cell. Fill the cells up to about 1/4 inch from their tops with a good commercial potting soil. Set the flat in a container of warm water until the soil surface feels moist. Remove it from the water and allow it to drain for about two hours.
Squish the excess pulp off of the passion vine seeds with your fingers, but don't clean them off. Plant a single seed about 1/2 inch deep in each cell of the starting flat. Set it in a brightly lit, warm spot out of direct sun. The top of your refrigerator or above a hot water heater are good choices. Your passion vine seeds will sprout in about 10 to 20 days.
Check the seed flat every day to make sure that the soil doesn't dry out. Keep it evenly moist.
Step the seedlings up to their own individual 4-inch pots as soon as they've grown large enough for you to feel comfortable with handling them. Set them near a warm, brightly lit window out of direct sun. Water the seedlings enough to keep the soil evenly moist.
Transplant your passion fruit vine seedling in a well-draining spot outdoors in full or partial sun when it's about 10 to 16 inches tall. Water it enough to evenly moisten the soil, but don't soak it to the point of being soggy or wet. Keep the planting area evenly moist throughout the growing season.
Apply a 1- to 2-inch layer of organic mulch. This will help retain moisture and discourage weed growth.