In the meantime I found out some things:
If you send a sim on a journey the green smoke will have stopped after his return.
The plants do not properly display what they need, nonetheless. I have some plants that need water, their soil is as brown as the others', so I have to click each plant to see what it needs.
Also the insect houses seem not to produce any fuel, although the insects are fed and checked.
The gardener appears only to show up every second day.
For a try, I deleted the lot, got out of town, got back into town, downloaded a new one from my gallery (the same one, but from the gallery) and settled a random sim there. The plants grew fine, could be harvested, until I logged out for the night. When I logged back on everything was as before: Plants dying, nothing in the garden worked.
It is not a big problem, as I have many fruits, vegetables and flowers in store, but the flowers are needed for flower arrangements and washing, the fruits and vegetables are needed for cooking, and I simply cannot understand why nothing happens from the side of the game developers.
Kind regards