This sounds like a glitch, but there is a solution with Supernatural. Get an empty room in your sims house. I tend to use a basement. Place some planter pots down and put a sprinkler in to save time. Using buy mode, move all plants into the planter pots. Unfortunately, your trees will have to stay dormant. Keep gardening as usual! This method will make sure that the plants remain awake throughout the year.
Just a quick question; When the plants 'Thaw out', do they have the actions greyed out?
Hope this kind of helps!