If you put the water bottle in direct sunlight, you'll make an oven. The seeds will germinate just fine in shade/partial-shade. They probably won't sprout above ground for quite some time. Normally, pawpaws grow a substantial taproot before appearing above ground. Many growers use bottomless pots or root-pruning type pots to grow pawpaws. Growing them in a pot with a traditional bottom will result in the necessity for significant root pruning before the trees can be planted out.

Young pawpaws are UV sensitive and should not be in full sunlight for the first year or two.

Keep them in a warm location inside and light is not necessary until they emerge. Seeds planted now may not emerge until July. Pawpaws normally emerge stem first like an inverted U and the tops have a slow and difficult time separating from the seed but this is normal. Don't expect to see much growth the first year.

Charlie I don't use the same method as a lot of people but I know what works for me and I have done it a lot. I soak my seeds 24 hours in water and at times add a small amount of vinegar to the water but it's not necessary. I then leave all seeds in the refrigerator in an old glass pickle jar wrapped in a moist paper towel until they sprout which is typically 2-3 months and then I start following the normal growing methods. PawPaws cannot take direct light as mentioned above until they get several years old. PawPaw seeds by what I have observed do not like to ever be dried out. Most seeds do better if kept damp from the day they come out of the fruit in my opinion.

I've grown cherries, apples, persimmons, pawpaws in the above manner and some others probably that I'm not thinking of. The above method for keeping them warm may work better because I have sprouted dates with the seeds wrapped in a moist paper towel in a plastic bag on top of my hot water heater.

I used 2 liter plastic drink bottles with the tops cut off and put them in a big Rubbermade tub with bottom heat,actually a heating blanket or throw wrapped around the tub,with it's own thermostat.The temperature was kept about 80F and most of them popped up in less than two months. Brady

Brady do you let your seeds dry out? I always have bad results if I let mine get dry. The pawpaws around here don't sprout once they dry out for some reason.

Pawpaw seeds are moderately recalcitrant. They'll take some drying, but not as much as orthodox seeds.

No,I try never to let them dry out at any stage.I think Kentucky State University put out information that the embryo can die and the success rate drops to less than 20%.

Brady,
I'm glad a university tested that because I did not know if that was just pawpaw's here or something to do with my methods but I get few if any sprouts from dry seed so 20% even sounds generous. Every time someone gives me some in an envelope like they were cantaloupe seeds my heart drops. Thanks for the confirmation and I found a link to the article you mentioned

Here is a link that might be useful: Paw Paw seed Propagation

After stratification I keep them in damp peat moss mixed with a light potting mix. I give them some heat (top of refrigerator/ shelf above a large screen TV etc. I check the seeds every couple of days and plant the ones that show a radicle . My planters are water bottles, soda bottles (big and little), juice bottles etc (these are free "tall tree pots". I usually cut the neck off the bottle and drill 10 or so holes in the bottom few inches of the bottle. When you plant them, put them in a hole and use scissors to cut slits in the sides and neck of the bottle to cause as little disturbance as possible. The radicle poking out of the seed when you plant it will often reach the bottom of a 10 ounce bottle in

3-5 days as shown in the pic