Is it possible (with seasons) to change how much it rains, snows . . .

[RainBeau]

You can build your own 'greenhouse' by just making a room covered in windows. Then you can use moveobjects on to move your plants inside and they will become active again. Just make sure to leave one section of all open or you can't move the plants in. As long as one piece of wall is open you can also plant seeds in the ground within the room. Just remember to put the wall back!

[Turoskel]

Thanks for the tip, I might try that later, most of my garden is taken up with horse equipment right now as I got pets at the same time as seasons, I locked the gates to the plant area but I guess this is also a good horse deterrent as well 

[Dellena]

I've also heard (haven't tried it), that if you use the 'moveobjects on' cheat, your sim can plant in the ground inside a closed room.