i'm not 100% sure, but my guess would be that one would need x amount of posts, or to be on the site for y amount of time in able to do a journal..
my suggestion would be to just keep on posting as you like to get your post count up and keep taking pix along the way with your new grow, and once you're able to start the journal, you can simply upload the pix into your journal..
i know, i'm sure that's not the answer you were looking for, it's the best i got..