I’ve seen people comment that it is not possible to easily add a +1 to your WordPress sidebar (widget bar) if your theme doesn’t have it built in. As you can see my site has a +1 Button and it couldn’t be easier to add it on your side.
What you need to do is to install this free plugin “HTML Javascript adder” . You can get it here!
After you install the plugin and activate it all you have to do is go to Appearance->Widgets. Find HTML Javascript adder drug it to the Widget area you want it to be displayed at (for my site it’s the primary widget area). After you can see it in the widget area click on it and paste the following code as in the screenshot below click save and you are ready to go:

<!– Place this tag where you want the +1 button to render –>
<g:plusone annotation=”inline”></g:plusone>

<!– Place this render call where appropriate –>
<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>Plugin image