The minimum post to earn merit is one post. You can make one post and earn several merits if the post is very useful and helpful. You can make hundreds of posts and no one will send merit to the posts because they are useless or of low quality.
Read what good posters are posting and start being like them. Post something useful and help.
Exactly my dear mate the minimum post and also the maximum post required to earn merit is just one post but it all lies in the quality of the post. It is not all about making numerous post or contributing in a discussion instead it’s about making a reliable and well constructive post and merits will come.There are various patterns to post and it’s always advisable that you post on your areas of interest and focus more in writing something useful and something that will benefit every member of the forum and merits will come. The shocking part it is that sometimes you write just four lines but the contents of the lines are beneficial to the group and before you will wake up merit will come.
Lastly, it’s not all about the number of post but the content of the post and the quality of the content and how beneficial it is to the entire group.