With spam comments on the rise, it’s becoming more common of a practice for bloggers to disable commenting on older posts. (WordPress even provides an option to disable comments on posts older than x days.) This drastically cuts down on the spam, as spammers tend to target pages that have an established search ranking. Unfortunately, it also kills the discussion.
Guess which posts on this site receive the most new comments every week. Older ones. Not the latest posts, but the ones that have stood the test of time and still have people looking.
The terms sometimes used to refer to posts that remain relevant, and bring in traffic, for years are “evergreen content” and “pillar content.” I have posts that are a few years old, are still the most popular in terms of traffic, and gain a couple new comments every month. Occasionally a spam comment will appear on those posts, but they’re outnumbered by legitimate comments, continuing a discussion that has been going on for a long time. Does it really make sense to put an end that, and frustrate readers who arrived a little late but still have questions to ask or opinions to voice, just to avoid a few spam comments Akismet happened to miss?
That seems like a wasted opportunity. Instead, you could update your evergreen posts to remain relevant, and add some links to more recent posts on the same subject. Build user engagement and keep the discussion going.
Smaller blogs, especially, can’t count on timely social media-driven traffic. They tend to succeed more with long-tail traffic from search engines. Obviously you won’t get very many comments at all if the form gets disabled just when a post is becoming popular…
Fortunately, there is a nice middle ground. Some posts, especially ones that have attractive keywords in them but become less relevant later down the line, rarely see legitimate comments but are magnets for spam. I have a couple that seem to get a handful of spam messages that sneak past Akismet every week, but never have real comments anymore. With those kinds of posts, you could probably toggle the discussion off without inconveniencing anybody but spammers.