Well I hope that was the problem Does it have mycorrhizae added to the pro mix HP ? I was also wondering if adding perlite might have dried them out a little quick. I would try a presoak of the whole medium and then plant the seedling then let it dry right out it is just a thought. I use to run added perlite to my pro mix BX due to the added vermiculite I tried it a few times with pro mix HP and I found that the medium would dry out a little to fast for my liking The reason i was asking about mycorrhizae I think since they added that I have had a couple of suspect bales. At one time there was none added Im by no means trying to start saying mycorrhizae is bad by no means Im just wondering if it might go bad after awhile of being in the sun heat and cold and heat again might change it's structure.