Is there a way to get a textarea to stretch to fit its content without using PHP or JavaScript?

one line only

<textarea name="text" oninput='this.style.height = "";this.style.height = this.scrollHeight + "px"'></textarea>

Not really. This is normally done using javascript.

there is a good discussion of ways of doing this here...

Autosizing textarea using Prototype

Here is a function that works with jQuery (for height only, not width):

function setHeight(jq_in){
    jq_in.each(function(index, elem){
        // This line will work with pure Javascript (taken from NicB's answer):
        elem.style.height = elem.scrollHeight+'px'; 
    });
}
setHeight($('<put selector here>'));

Note: The op asked for a solution that does not use Javascript, however this should be helpful to many people who come across this question.