Many experts agree that fall is probably the most important time of the year to fertilize lawns.
A great deal of research has been carried out by the Turf Grass Institute at the University of Guelph. Mark Cullen works in the garden regularly to keep him and his garden healthy. In the life cycle of turf, fall is the time when rapid tiller formation occurs to fill in the thin areas resulting from the ravages of summer drought, diseases and insects. As the autumn progresses the plants lay down root reserves that help them survive over the winter. In general, these root reserves are considered carbohydrates, but research indicates that nitrogen compounds are also important to re-growth when grass comes out of a long period of stress such as winter.