Hi Don - bit of a late addition I know, but have only just joined the forum and spotted your title.
I have planted paw paw many times (UK based - so strictly for indoor ornamental use only), and have tried a couple of different types from seed, including one which was advertised as 'hardy', but have had a great deal of difficulty in getting young plants to survive. Germination was straightforward, but the plants rot extremely easily. Have lost quite a few plants in the same way, using different soils types, different approaches to waters (from plenty to almost none!), and different locations both home and office! Very dispiriting as I am a bit of a tropical plant enthusiast.
Just so happens my dad has worked in horticulture in the tropics for many years, and have asked him pretty much the same questions as you've asked, in the light of my failures, and my understanding is that even in their natural habitat they are not a very robust tree anyway and will often disease and die with little obvious cause.
There's my little contribution (and sorry it is so negative :-(
Tom.
