Another evidence

My son wrote:

Another evidence of spring is the blooming flowers.

I want to explain why this is wrong but I can’t. My best attempt is that it feels wrong. I want to correct it as:

Another piece of evidence is that you can find blooming flowers.

But that feels clumsy.

Why is what my son wrote wrong, or not wrong?

What is the most natural way to write it?

I want to explain why this is wrong but I can’t.

This is because evidence is a non-count noun, so you can't talk about "an evidence" or "another evidence".

This was previously addressed in the question, "Is 'evidence' countable?"

You could talk about "more evidence" or "further evidence" to avoid the wordier (but just as correct) "another piece of evidence".