This is starting to really annoy me but it seems as if plants are not meant to respawn. I've been playing since the day the game came out and in some cases (like all of Riften) I've never seen any plants respawn. I've been searching alot for an answer but can't find any. The thing is some plant gathering-quests and alchemy-leveling becomes much harder when plants never respawn. Is there a reason why most plants never respawn? Is there a reason why this bug haven't been fixed?

This is a game engine bug that has never been fixed since the 1.3 patch broke the flora respawn system way back at the end of 2011. There is no solution to this issue. Bethesda has never bothered to fix it in all this time and sadly probably never will, because they have moved on to other projects. The only suggestion that I can make is to buy ingredients from merchants for mixing your potions.