There are a few options to control who can create comments and when those comments can be created on blog posts.
The primary options are located with the Post Options panel. To get to the Post Options panel, go to the blog to be managed, Manage > Manage Blog > Post Options:
Here, the following options can be adjusted to meet the needs of the blog:
Permissions related to commenting and feedback are managed for individual blogs by going to the blog, Manage > Manage Blog > Permissions. Within the permission list, the Create Comments, Delete Comments, Edit Comments, and Rate Posts permissions associated to roles control whether members can perform these commenting and feedback actions within the blog.