To add the google plus to every single post on your list layout you have to use the 'href' attribute to indicate the URL to be +1'd.

To do this, just log into admin area of your site, go to [Blog], [Advanced Layout Customization], [Blog Post List Layout] and paste the following code:

<g:plusone href="{ tag_itemurl_withhost}">

You need to use the tag { tag_itemurl_withhost} to set the right URL of the post. Easy.

And in your blog template please add this little code:

 
<script type="text/javascript">
 (function() {
    var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true;
    po.src = 'https://apis.google.com/js/plusone.js';
    var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s);
  })();
</script>

*Please note you need to remove the first blank space of the { tag_itemurl_withhost}