My trees are dormant in mild temperatures? (Answered)

I have managed to get around the problem by having big basement gardens. They are dormant for the first few hours after planting a seed. After than they carry on as if it were summer all year round even if there are blizzards outside.

Problem with basement gardens is the sprinklers don't work - but he Swift Gro Gardening stations, tractors and green dragons do work. And Sims can tend the gardens by hand if they aren't too big.

Alternatively you could have indoor gardens above ground.