Hello herbavenia,
H1 tag means Header 1.
Normally the header title of single.php (single post) is header 1 (or H1).
It looks like somehow, this is not the case.
Your “main homepage”, located at http://herbavenia.com/, does contain an h1 tag:
<h1 class="site-title">
<a href="http://herbavenia.com/" rel="home"><img src="http://herbavenia.com/wp-content/uploads/2015/09/logo-e1446473955281.png" alt="Herbavenia"></a>
</h1>
The page you linked is a default theme page. The theme sets the page title for pages with an h2 tag. So, unless you add an h1 title in the page content, the page won’t have one. The other option would be to copy the parent theme /inc/page-title.php file to the same path in your child theme. Then change this:
<?php elseif ( is_page() ): ?>
<h2><?php echo alx_page_title(); ?></h2>
to this:
<?php elseif ( is_page() ): ?>
<h1><?php echo alx_page_title(); ?></h1>
If you make that change you’ll just need to remember not to add an h1 title in your content since search engines are generally expecting only one h1 tag on a page.
