Everytime I get turned into seed my character cannot move.
As far as I know, that is the intended affect. It stuns you and heals you a bit. Probably not the best option for solo players because most likely the mobs attacking you will do the required amount of damage to finish the job. In group play though I believe it can be healed so would be helpful to keep you alive if something goes wrong.
Even after the seed expires my character is not able to be moved after I die and release.