I try to use mostly organic methods and I picked up a tip that its best to spread mushroom compost or other compost in the winter when the ground is frozen - after Thanksgiving usually- but before getting a lot of snow. I don't recall where I picked up that bit of information but it really stuck with me so I'm sure it was somewhere reliable (I hope!). The reasoning is the snow will pile on top of the compost and when it starts to melt in the spring it will bring the compost down into the soil really well and give the plants a nice boost for spring growth right when they need it. But you wait until the ground is frozen because you don't really want to fertilize at the time you put it down, it's another layer of insulation in the winter and then gives plants a head start in the spring.
From your post, though, I'm also not sure what your asking. It seems like maybe you're asking about fertilizing to winterize the plants like you'd do on a lawn? In that case i think it's best not to fertilize at the end of the growing season.
