I'm practising scales for Grade 5 piano and I know you can choose either melodic or harmonic minors - but do you have to do all one or the other or can you mix or match? For Grade 4 I did all melodic but it's just occurred to me that maybe you can choose for each one? Sorry - did warn you that it was a silly question!

I believe you have to do either melodic or harmonic. Not a mixture of the two.

Edit: In the front of the books it says "..harmonic or melodic at the candidates choice"

You can mix and match.
Unless it says so in the syllabus (don't think it does) you don't need to say (or even know ) which you are doing either.
I asked officially on behalf of a grade 2 student a couple of years ago.

Well..you live and learn! In all my grades, my tutor has stipulated either/or! Thanks for that.

Thanks!

Whether you can mix & match or not surely it must be easier to learn them all the same?

Some I find easier to play harmonic though largely I favour melodic.
When I first started to play melodic minors I wondered why they are usually taught second on piano as I find that generally they lie much more comfortably under the fingers.

I did melodic minor scales for Grade 5 for that reason. And then I found I had to learn some of the harmonic minors as well for the contrary motion scales, and decided that that was the main reason pianists tended to do harmonic minors.

I've learnt both of them but sometimes one just seems to be easier than the other so I want to choose the ones that give me less of a chance of screwing up!