Plants, bushes, mushrooms etc?

In the outdoors, it's 10 days, as long as you don't enter the cell in that time. If you do, the timer resets and you have to wait 10 days again. Indoors, I believe they reset when the dungeon/cave does, so 30 days if you cleared it, 10 if you didn't.

Just don't touch your garden when you buy a house. They never grow back. Over 6 months and I made sure I stayed out of Winterhold and the college. First day back in Winterhold and I get arrested for $40 septim bounty. Then I go up to my quarters at the college and my garden is still bare. I tried the same thing with the garden in Riften but only 2 months. Garden is bare. Everywhere else things grow back quite quickly sometimes.