It all depends upon the overall size of a tree. A larger tree has more roots, and greater capacity to draw moisture and nutrients from the ground, and consequently has a greater potential for growth. A large tree may add 2-3 feet to branches per year, while the sapling you described may only grow 12-18" per season in height. You must protect these little guys until they are larger! You don't mention this, but either use a long stake, or set up a couple of stakes close by around the perimeter. Birds will see the tree as a convenient landing spot, and they can easily snap the graft off. In sunnier locations it's advisable to keep shaded for a couple of seasons, but in Zone 6 you probably won't have to worry about this. If you did shade them, the structure you put up around them would also protect them from damage...be it birds, wind, children, or flying debris. -Bruce

You may be better off doing bark grafts with that size trunk. Do several all the way around the stump, and then select the strongest for the new top. The others will help the cut heal over. The stock will try to push lots of new growth, so you may want to rub the new shoots off to force all the new growth from the scion. Another option that may be less risky, would be to cut the top, then let new shoots grow up from below the cut, then chip bud to them later.

Pawpaw is considered an understory tree and grows rather slow. You may consider shading the pawpaw for the first two years until the taproot has a chance to grow.

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