How do I separate my categories in sidebar

All of my posts are showing up under the same heading in my sidebar.

like this

Catfishing Articles
Catfish post 1
Catfish post 2
Catfish post 3
Smallmouth post 1
Smallmouth post 2
Smallmouth post 3

I want them to have a separate heading based on which category they are in.

Like this..

Catfishing Articles
Catfish post 1
Catfish post 2
Catfish post 3

Smallmouth Articles
Smallmouth post 1
Smallmouth post 2
Smallmouth post 3

How do I do this?

Here is the sidebar code

<!-- posts -->
	<?php
		if (is_single()) {
			$posts_widget_title = 'Recent Posts';
		} else {
			$posts_widget_title = 'Catfishing Articles';
		}
	?>