FERTILIZING IN THE AUTUMN
You CAN fertilize in the autumn. Often you will read that you shouldn't fertilize at this time of year, and generally that COULD be true.
What happens is that if you fertilize late in the summer (late August-early September) you could force a flush of green growth. This growth will be very "soft". If we get an early frost, it will be "nipped" and die, stressing the tree, or shrub. Or even grass for that matter!
However, if you wait until after the leaves begin to fall, you'll be close enough to the time of frost that the plant will NOT put out that flush of growth. Instead it will store that fertilizer right by it's roots, gobbling it up all winter and being ready to burst forth when the spring warmth and rains filter down into the ground.
As I told the gardener that questioned me on this issue, you really have to be keenly aware of your garden and it's micro-climate. You are the best judge of when any new growth has stopped and when it would be safe to fertilize. Use that judgement. If you goof, hey, the world won't come to an end. Next year you'll have a better idea. Remember it's almost impossible to kill off a garden in a year! :-)
As far as the grass is concerned, if you do a late fertilization, remember to rake the fallen leaves FIRST! If you don't, it will be a VERY patchy cover...and then when you rake up the leaves, the fertilizer will go with them. A huge waste of money AND fertilizer!!!