There is a law in France that answers this question very quickly (Remember, we are in Paris). Yes, you do need a diploma. Like in the cosmetic industry, the organic sector needs to comply both with conventional regulations and the rules for sustainability.
To the question: Should you need a diploma to be an organic hairstylist, we can offer a more nuanced answer.
France puts a lot of stress on academic training. This demonstrates a willingness to push students towards excellence and have them engage deeper into their fields of choice. However, this can have a very advert effect: giving more meaning and importance to the diploma itself, rather than the education it is associated with.
Because of that, you sometimes see hairdressers who have had their degrees for 20 years but who have never trained since, in order to keep up with trends, techniques, etc.
Besides, the way hairdressing is taught in France does not exactly match the reality of the market; especially for those who want to go into sustainable salons. (We do know, however, that it is not perfect in other countries either, like in the USA).
Our opinion, for hairdressing in general but mostly for organic hair care, is that a 6-month training should be enough to know the trade and to get to know one’s own strengths and weaknesses: i.e. if one is better at cutting, coloring or styling (to make it short). After that, junior stylists should be strongly encouraged to learn continuously and most of all practice and practice some more.
Of course, some technical knowledge is needed (for bleaching and coloring for instance). In organic and sustainable care, it is less intensive as the products are less dangerous; but one needs to be taught how to save water and energy but also how to use coloring (tinctorial) plants.
With the new French law, which should allow more freedom when it comes to opening a salon, there will probably be more competition (just as hairdressers are fearing), but the Canadian experiment has taught us that when there is more intense competition, only the less skilled disappear. Those who are passionate, who love their trade and are demanding with themselves have nothing to fear.