I used to henna for a long time. Than, about a year ago, I had roots of 3-6 moths. I had lots of other stuff going on, some of it affected my hair - I was quite a mess and decided to, at least, put my hair in order to look nice. So I had to do a cut (lots of thinning) and decided not to henna until I decide what color I want. Henna started washing out in a weird color and was getting too dark brown for full head applications every time. I also used to Manic Panic every now and then in between. But, I had to color it, coz the washed out henna, MP and the ashy-blonette roots - it all looked messy (and not good for my job). I went to a fancy, expensive salon (wasn't in one for about 7 yrs) and found a hairdresser who knew about henna. He warned me about all that can happen when messing with henna, but I said it was all baq and good quality henna. In the end I decided to go a medium brown shade. He did an awesome job covering the henna and the red/orange glow. He did 2 full head colorings (2 separated visits, almost 3 months apart), and after that was roots only (did that just once btw).

Long story short, I was veeeeery afraid to go to a hair salon, but I got lots of compliments after that. And was totally surprised to find out someone who knew about henna and how to deal with it without freaking out and all the false information I usually heard. And I live in Croatia where, until some years ago, you couldn't even find henna (the "pure" one, not talking premixes or Lush). So, go to a salon and talk to them. Ask if someone has experience to deal with henna (or maybe ask on a local forum where to go?). You can always say you need to still think about it and that you will call when you decide, and go to another salon if you're not satisfied with their answers

Btw, I like how your hair looks atm