PHP: Date larger than current date

I have this code:

$curdate = '22-02-2011';

$mydate = '10-10-2011';                     

if($curdate > $mydate)
{
    echo '<span class="status expired">Expired</span>';
}

This would echo expired BUT shouldn't because $mydate is in the future and therefore smaller than the $curdate but PHP is looking at JUST the first two numbers 22 and 10 instead of the whole string. How can I fix this?

Thanks