We used a commercial potting soil, the plants were in 3" pots and about 4-6in tall when planted. We killed a plant when I shoved the roots through the hole. My wife tried again by threading the plant through the hole.
Why we aren't rotting off stems?? I don't know, we had some water dripping through initially, which seems to have stopped now. It has been cool and rainy since we planted them. For the most part we have let the rain water them, but now the weatherman tells me we have some sun ahead of us. Today was the first full sun since I don't know when. Now we need to figure out how much water they will need. Seems that too much water would lead to what you describe, I will keep a close eye on these and post more pics.
My wife bought a pack of 6 plants, I killed one stuffing it into the TT, the other 3 have been stuck into the ground, they are doing ok, but not nearly as well as the 2 in the TT.
It's too late to get any pics tonight, I will get some tomorrow. The last pics were taken on 5 Jun. I have pic from the day we planted, 5 May, but Photobucket doesn't want me on tonight, so will try again tomorrow.