What kind of fertilizer are you using and how often?

I have never fertilized it. And it's in the original soil. What type of fertilizer should I use? I have compost, all sorts of regular fertilizers, and worm castings....any of those good?

Yes but it was getting about 4 hours of sun inside, and the leaves were like that before I put it out. In person the new growth still isn't a rich dark green like you'd expect. Maybe I should take it to a local nursery and see what they say.

I agree with rhizo. Your Rosemary looks hungry. I would repot it in new gritty fast draining mix. When it has settled in start feeding it. In the ground it never needs fertiliser but in a pot it would need some. I can't advise on when or what because I have only ever grown it in the ground.

Thank you very much. I will do that.

Agree with floral and rhizo. When fertilizing, you can use any water soluble fertilizer - whatever you would use for any indoor plants or outdoor containers.