I am sure there are experts here, and I don't consider myself one. But if I had to take a guess, I would say over-watering and not enough sunlight.

But again, wait for a response from someone far more experienced than me. My garden is thriving, but I have no idea what I'm doing, lol!

They just get good morning and afternoon sun, and the plants will let you know when they need water. I learned here that rosemary, particularly, doesn't like a wet soil, so I hold off on watering it as regularly as I do the others. Sometimes over-caring for an herb can be the trouble.

I am growing some rosemary, basil, cilantro and flat leaf parsley indoors. I am careful not to overwater and they get good morning sun and a room full of light in the afternoon. They seem to like that. No problems yet (fingers crossed).

yup, overwatering and not enough sunlight.... oregano sage and thyme like good drainage, MODERATE water, and full sun.
stick your finger in the dirt, if it isn't dry an inch down, they don't need water.

The other side of the coin..... You may be watering, but is the soil absorbing the water? I recently discovered why a potted plant wasn't doing well. When I pulled it out of it's well-watered pot I discovered that while I was watering the pot the lower soil wasn't even getting wet... just going right around the out side of the soil mass. I plunged the whole pot in a big bucket of water and it took hours for the soil to re-hydrate. I've since pulled-off most of that soil and replanted with the soil I prefer from MiracleGro.

You've got a batch of mismatched herbs all in together! Like, mint prefers moist conditions, sage and thyme prefer dryish conditions. I never had more than one kind of herb in the same container. One will always out-compete the other.

I'm also wondering what size container you have for that large crowd of different herbs. People tend to forget that herbs can get BIG! Mint and oregano, for instance, will take over the world, if allowed. Even 'little' thyme can spread 30cm in all directions.

I suggest you put each herb into its own container, then water it according to its needs. Potting mixes will become water repellent if allowed to dry out, but very few of the common herbs will tolerate soggy soil. I'd say watering has been your problem - either you've overwatered, or you've underwatered - either way, you're killing your plants. Do the Finger Test - poke your finger in as far as it will go. If the tip of your finger feels dry, water the plant, if wet, don't water. If completely dried out, put the whole pot, plants and all, into a larger container of water and leave it there until no more air bubbles come to the surface. Then allow the excess water to drain away.

Also, every plant has different requirements for sunlight. Is is REAL sunlight they're getting, or the filtered sunlight through a glass window? Except for your parsley, all the others need as much sun as they can get - like a minimum of 6-8 hours per day.

Thanks. I'll water them less, see if it helps. Unfortunately, window sun is the best thing I can do for them. Also, I have the mint in a different container. I thought mint liked moist soil, but it seems to be doing the worst. How often would you recommend watering? I live in CO, and it's a pretty dry state, but I don't know whether that affects indoor plants.

AHA! It is perhaps the sunny window that is causing the crispy leaves. Are they getting sunburned from the sunlight being magnified by the glass?

Yes - crunchy means dry and dead, or cooked. Windows are famous for cooking plants.

Also it's often dry inside so a humidity tray might help to keep the leaves from dessicating.

I hungmy herbs outside on a rack onthe porch to dry. They have been handing there several weeks. They are brown and crunchy? Are they still good?