Sometimes you will hear people say to let the grass grow tall right before winter sets in. Their reasoning is that the extra foliage will insulate the crown of the plant from the extreme cold of winter. Although this may sound reasonable, in practice it probably does little, if anything, to increase winter hardiness. On the contrary, a canopy that is too high during the wintermay lay over and become matted down, leading to an increased
incidence of winter-diseases such as snow mold. Turfgrass species vary genetically in their cold tolerance, with warm-season grasses being less cold tolerant than the coolseason types. Given these differences, cold tolerance is improved by increasing the health of the plants going into the winter, and healthy plants are a result of a sound management program (fertilizing, watering and mowing) during the spring, summer and fall. The lawn will benefit more from continuing to mow at the recommended height than from trying to gain some insulation against winter cold by allowing it to grow tall. – Kansas Turfgrass Foundation- October Newsletter