Comments are a very important part of blogging and a great way to receive feedback which you can use to engage with your readers. However you may not need comments activated if you are using WordPress as a static website or for some other reason.
There’s different ways to turn off comments.
You can do this manually or install a plugin
Disable Comments Plugin
One of the most popular plugins to turn off comments is named Disable Comments
This plugin allows you to disable comments on all posts types as well as remove the comment fields from your Edit Post screens.
Disabling Comments Manually
Another option is to turn off comments on existing posts and future posts.
To turn off comments on future posts, navigate to Settings > Discussion and deselect the box next to Allow people to posts comments on new articles.
To disable comments on existing posts, navigate to the All Posts screen and check the box next to Title to select all posts. Above this box, select Edit from the drop down then click Apply. This will allow you to bulk edit all posts.
You’ll need to go to the comments section in the bulk edit drop down and select Do Not Allow from the drop down. See more in the screenshot below.
The manual method only allows you to bulk edit 2o per time which may not be suitable if you have a large number of posts therefore the plugin will do the job faster.
Turning Off Comments Per Post
Simply scroll to the bottom of each post and select the deselect the Allow Comments box.
If the Discussion module isn’t displaying at the very bottom of your Edit post screen, go to screen options in the top right hand corner and check the Discussion box.
Deleting Spam Comments
Personally i use the WP Optimize plugin which allows you to bulk delete of comments marked as spam and unapproved comments.
If you want to delete all approved comments you can using phpMyAdmin
Enter the query
[php]DELETE FROM wp_comments WHERE comment_approved = 0[/php]
You can also delete comments by date using phpMyAdmin Database queries.