One of the questions I am asked frequently is why we fertilize lawns in the late fall.  The grass is going dormant so why give it food.  The picture below may help to answer that question.  We recently had a utility service do work in our front yard and sod was needed after the work was completed.  The sod was installed mid December.  The picture was taken of that sod in late January.  If you look closely you will observe many inch long white strings.  These white strings are new roots that the sod is producing.  This growth occured since the sod was put down six weeks ago.  In that time we have had a mixture of temperate winter weather but also a 10 day period of very cold and a few days sub zero.  In those days where the thermometer rises above freezing, while the grass leaves themselves appear dead or dormant, underneath the lawn is still quite active.  This activity, illustrated here by the new roots produced by the sod, is why we fertilize late season.  This new root growth will not only occur in sod, but in your existing lawn as well.  Those lawns that  have an ample supply of nutrients will grow stronger and thicker as they produce new roots, and once the spring sunshine warms the ground they will out perform those lawns that have been deprived of nutrients.  So does grass grow in the winter?  Absolutely.try this