She may play the style-challenged Hermione Granger in the ‘Harry Potter’ films, but Emma Watson knows what’s important in fashion.

When did you cut your hair?

About three months ago — I didn’t tell anyone I was going to do it. I went into a hair salon in New York and took a couple of pictures of Mia Farrow and said, “I want to look like this —make it happen.”

Over the years you’ve earned some serious sartorial credibility. Are you working on anything fashion-wise?

I just did an organic clothing line with Alberta Ferretti. Alberta wrote to me and said, “I saw what you did with [ethical brand] People Tree and I think it’s a great idea, would you do something with me?” I was like, “Yeah.” Jane Birkin was my inspiration for the collection — classic French, ’60s Jane Birkin.

Why is organic and fair-trade fashion so important to you?

I did my A-level coursework on the developing world and fair trade and practices in the garment industry, and I found it really troubling. I would work for anyone for free if they were prepared to make their clothes fair trade and organic. Something like one percent of clothing is made from organic cotton, which is a shame because it seems like environmental and ethical presence is really making its way into supermarkets and so many other areas. But clothing, for some reason — people don’t seem to question where their clothes are from. That’s why I wore vintage [at the “Harry Potter” premiere].

You have a close relationship with Burberry. Have you ever considered doing something similar with them?

I’d love to persuade [Burberry design chief] Christopher Bailey to do even just a section of Burberry that was organic or fair trade. I love him; he’s a very good person and an amazing designer, and I have a lot of respect and time for him. [Ethical clothing] is something that I want to champion, it makes such a huge difference to the lives of the people who are making it and the environment. The impact is epic.