Done and nothing was hiding in it.

I'm baffled. As you can see, I've been keeping it somewhat watered. This heatwave has not helped, but everything else is struggling about the same level?

Baffling, indeed. It's not simply struggling, it looks dead as in deader than a doornail. If there's nothing going on down at the root level, I really don't have any idea what could have caused its demise. Your other plants look fine.

Exactly. I have no idea what caused it, so I can't avoid it, and it's been beautiful for years. I already bought a replacement. Even though I grew that one from seed it's going to take so long to get back to the size it was. 🙄

I guess the part that is bugging me so much about it is that it was literally overnight. One day was fine and lush, the next it was completely dead. So frustrating

Could an animal have urinated on it? Cat urine will really do a number on plants.

Is it root bound? That wouldn't account for the overnight death unless it was a bit slower than you think.

I suppose? But just that plant? It's on a deck that's up stairs. This deck is 12 ft high? Nowhere near the street? I doubt it.

And, there were actually a couple of smaller seedlings in front of it, and they're not affected at all. When I smashed the plants together, I took them out of the picture.

It just is not something simple. I give. Nature won, and the mystery may never be solved. Regardless of how frustrating it is.

The overnight sudden death is perplexing. What type of pot is it in? Were temps over 80 degrees?

Perhaps the thyme succumbed to a combination of factors that literally scorched it - dryish soil, extreme heat, hot wood decking underneath it.

So nothing else was scorched, but that's your suggestion? What about the Rosemary? Or the more delicate dill or mint? No. That is not it. What about all the other years it was scorched? This is not the answer. I appreciate you trying 😉

Everything has a life span. That includes thyme. IME, individual plants aren't very long lived, and when their time is up, they go. Since I always have seedlings, at this point I just clean up the mess and move on.