I'll often leave plants at neighbour's properties. Stuff like a line of onions or roses just sitting ready to plant. A sim with the Always Welcome and extra friendly traits can start planting and quite often the property owner will come along and help out. It's actually rather sweet to see.
As far as leaving harvestables, I've had mixed results there. Sometimes the house owner won't do anything with the harvestable. It just sits there, week after week. Sometimes when switching to that family to control them, I am only presented with "eat (whatever)" and "clean up". If I leave stuff outside on the ground I also get the "plant" interaction. I don't get an option to add it to their inventory. I can't recall if I can drag and drop it into a fridge or directly to a Sim's inventory though.
