Google+ now allows users to lock their post and disable comments before sharing. This feature is added after users raised request to allow them to block the comments even before its published. Earlier if you wanted to limit the sharing of a post by locking it or disable the comments then you had to firstly publish the post and then click on the Post options to lock it or disable comments. Using comment disabling options users can also create poll on Google+, the feature which is still missing in Google+.
Now once you are done writing your post and added the circles you want to share it with, just click on drop down button next to “Add more people” option in Share box and then choose ‘Disable Comments’ or’ Lock This Post’ or both.
Here is an How To Video by Google+