Hey, glad you like the game so much.
If you're on PC, I could take a look at this (unfortunately I no longer have a Mac and changes to MacOS policies mean I can no longer support it). My guess is that the save file has gotten so big it's taking a very long time for it to generate all the plants that you've made. You can find the save files at C:\Users\"account name"\AppData\LocalLow\OwenBellGames\Mendel. Send them to me and I can take a look at what's going on.