I have mentioned verticutting in a couple of posts and thought I would explain more in depth. Traditionaly grass is cut horizontally by cutting the top of the leaf off with either a rotary mower, the style used on most home lawns, or a reel mower. On the golf course we use reel mowers on the greens, tees and fairways and rotary mowers in the rough and clubhouse grounds. A picture of a reel mower unit is below.
When we veritcut greens we use a unit which has multiple blades that look like circular saw blades. They cut the grass vertically, cutting the stolons and rhizomes, also known as runners. This helps to thin the grass canopy and encourages new stolon and root growth. It is helpful to verticut greens before a topdressing to open up the grass canopy to give the sand a place to settle. An example of a vertical mowing unit is below.