Order By Meta_key but convert custom date to Y-m-d first

I actually found a cool value for the orderby option in this case.

meta_value_datetime

It works the same as using strtotime and the date methods in PHP. So here is my final code that started working:

$wp_query=new WP_Query(array (
        'post_type' => 'sermon',
        'meta_key' => 'sermon_date',
        'orderby' => 'meta_value_datetime',
        'order' => 'DESC',
        'posts_per_page' => -1
        )
    );