Needs more light. Could be drowning. Mint likes its soil moist, not soggy. Dig it up and put it somewhere else, where there's more sunlight and better drainage.

thanks daisy.

Can I piggyback on this thread? My mint leaves are PURPLE. Not the purple tinge you get underneath tomato leaves when the plant gets too cold, but NEON purple. My mint has suffered various misfortunes, including getting attacked by an undetermined bug, getting sprayed with bug repellent meant for humans, and, most recently, getting pounded with two weeks worth of pouring rain while living in a jar with no holes in the bottom. Do you think it was this drowning that caused the purple leaves? Is there something I can do for it now?

{{gwi:889972}}

It does appear stressed. The new, green leaves are a good sign.

I would move the plant to a container with drainage holes. Although moving a plant from a rigid pot with no drainage holes (appears to be a glass jar) can be difficult at best. It can be damaging to the plant and you may have to "dig" the plant out or break the container. Avoid these containers in the future.

FataMorgana

Don't worry about damaging the mint when you pull it out of the jar...even a tiny piece will grow back to a full sized plant.

thank you both for your very helpful responses. I have several kinds of herbs in these glass jars, so I will look into getting a drill bit for glass when I go to home depot today.