Those pots are doing what they should do, it was the only thing I could think of that might be slowing them down. I was also thinking you should give them a little of something to help out while they are getting their roots in properly. I was thinking bone meal as its low in N, but would take time to break down, that seaweed mix should be perfect, you dont want anything high just in case they have plenty already and its just a case of them getting their roots into it and they end up over fertilized.
Sorry Badger, did I rudely awaken you