Student blogging

I made a new blog for students in my fourth grade class last month. Two problems with it are finding enough time for students to blog at school and how to enforce some standard for appropriate length and conventions, especially spelling and punctuation. Students are prone to think of the blog as a place for short messages such as "Hi, how are you?" and I would like them to use it as a place for more thoughtful posts and responses. Eventhough many of the posts and comments are in my mind too short, still it is providing them a place to communicate. It is another place for them to experience written language in a meaningful way and I think that makes it worth the time it takes me to set it up and the time it takes for them to use it.