If there is only one time you can fertilize your lawn, Fall is the optimal time. Soil temperatures are still warm, and grass plants are taking in nutrients and storing them as energy for next Springs new roots and shoots.
Broadleaf weed control is good in the Fall, even though results are slowed by cooler temperatures. The same as other seasons, the most important part of weed control is good contact with the weed leaf surfaces. Foliar sprays give the best contact. Granular applications should be applied to damp grass, such as early morning dew. What might take weeks in the summer to kill weeds, could take 3 weeks in the fall.
Lawn aeration can be accomplished successfully almost anytime the lawns are not too wet. Fall aeration allows air and water to move downward through the thatch area and help aid the natural decomposition of thatch. Weed seed germination in the fall is minimal. Any soil brought to the surface is less likely to add weeds.
De-thatching is more stressful on lawns then aeration. Fall de-thatching is less likely to damage new roots and shoots that are produced in spring growth. Still, if fall de-thatching is done, it would be a good idea to fertilize afterward.
Lawns should be continued to be mowed as long as they grow. Tall matted down grass and leaves contribute to winter lawn damage and disease. Leaves should be either raked or mowed until they are very small, and almost disappear in the grass.