A community can start a blog as soon as it can build the support and resources to keep it active and interesting.
From the blog post
So how does my site get a community blog?
Starting a blog is easy. Keeping up a blog, contributing to it regularly is difficult. Blogs are hard work. Wanting a blog is obviously the first step, but there are a few things that the community needs to discuss in order to get a blog going.
Raise the idea on the child meta. A community blog needs the involvement of community members. These blogs don’t exist to be the personal blog of a community member. They are both for and run by the community. It needs to be something the community collectively wants and will cultivate.
Define the scope and purpose of the blog. Is the blog about the site? Is it about the site’s topic? Is it about the industry around the topic? Keep in mind the audience of your community and their interests. Another generic blog about may not be all that interesting. A community blog should be interesting to both current members and potential new members.
Recruit contributors. Who will write entries for the blog? Starting a blog is a bit like going through the buffet line. Be realistic – don’t let your eyes be bigger than your stomach. Think seriously about if and how often you will be able to contribute a blog post, including research/prep time. The more contributors there are, the less frequently each contributor needs to post. One post a month is a much easier to stomach than a couple posts every week.
Plan a schedule. Given the results of steps #2 and #3, think about a rough idea of a schedule for the blog. Will there be one post a week, posted Mondays? Will there be posts on Tuesdays and posts on Fridays? You don’t need to be pushing out posts daily, but you should post at least once a week.
But this community has barely started. I would suggest a little community-building is the task at hand before you start discussing a community blog.