Right now, Google pulls in the text from the homepage (blog archive) for the description text in my indexed homepage, and it doesn’t really make sense… actually looks sort of spammy.
Is it possible to use JS or CSS to specify to Google what the site description should be (similar to what all those SEO tools out there allow you to do)?
Hmm, I don’t think so. As far as I know, Google is going to look at the raw HTML and not run any Javascript when crawling your site.
So the best route would probably be to flip things around, and use the blog’s Description field for whatever you want to show up in search results, and then hide it from human readers via the CSS on your blog.