Plants no longer change their quality or evolve on their own after Sims traveling.
Fixed in Patch 1.68.154/ 1.33
If you're still experiencing this issue, please create a new thread.
@HechiceraSim I personally just tried getting rid of the eco footprints. Now this is an ongoing game so maybe it is just permanently bugged from having eco footprints from the start. I don't know, but once I unchecked the option for eco footprints and harvested my plants, they all degraded to nice quality from perfect quality. I ended up so frustrated I needed a break because for me the one thing that is game breaking is when my plants are messed with. I love gardening and to see that happen was just a shock. I felt sure a neutral, non existing eco footprint would save the day.
So now I'm left with trying to restart my game with the eco footprints turned off from the start which I'm finding a hard time motivating myself to do as it will have been my 5th restart of the game to try and weed out the unplayable bits as best I can...or go back to eco footprints and just keep cheating my way up to a green eco foot print continually because I've noticed they do stay perfect in even a cheated up green eco footprint. I noticed with the MCCC mod I can go to my vast garden and cheat them back up to perfect, but that takes a really long time, especially when you start from a nice quality.
@PriestessAvenara: for a work around:
You can create a room with all your perfect plants, save this 'hortus botanica' in your library, and use it in your new save. My experience so far is that they stay perfect!
