I know this is a common problem, but I have yet to read any description of what I've been seeing.
I was growing both cilantro and parsley in a pot, and had started summer of last year. I brought it inside and continued growing it over the winter. I then replaced the soil because it had been a couple of months and my cilantro had started dying ( I assumed it just needed fresh soil/nutrients). After the addition of fresh soil while the cilantro seems to have permanently died, parsley started to sprout again. They're still small/babies (they don't have the large leafs, still look like minature fern trees), but I've noticed the edges of the leaves start yellowing. I also want to reiterate, I have not added new seeds. This is the same plant from a year ago, just in a new pot, sprouting its own stuff.
In terms of growing conditions, I have it outside 24/7, moved it outside about a month ago. I live in CT, so it does rain around 2x a week, but I do still water it every other day if it hasn't rained in sometime and if the soil looks like its dry (especially now that we have hotter days). Its in my balcony, so it doesn't get a lot of sun, but it does get around 3-4 hours each day. I should mention I have tomato and basil growing in separate pots, without problems from either of them (using same soil, same conditions, water them all at the same time). They don't appear to have any issues.
I've tried to read up on what it could be, and theres bacterial growth, fungus, parasites etc. However, there is no yellowing spots, roots look fine, and I haven't seen any signs of parasites (not to mention my other plants next to it are fine). There is just a lot of info out there, and all of it is full blown yellowing, nothing about the start (slight yellowing at the edges).
Any help would greatly be appreciated!
Added a photo. The yellowish stems are from my dead cilantro. You can see on the left the yellowing I was discussing. The little baby ones sprouting next to it are still green, and don't have any yellowing.