Golfers use a method known as "reading" the green to enhance their chances of making a putt. Reading a green involves determining the speed, grain, incline, decline and tilt of the green on the line of the putt. Most putts are not struck directly at the hole, instead they must be struck to take into account the characteristics of the green to arrive at the hole at the proper angle and speed. The best players will read the green by walking around the green and studying the characteristics of the green before addressing the ball. Reading the green and putting are considered by many golfers to be the most difficult part of the game. The green is typically surrounded by slightly higher grass, cut at a height between that of the green and fairway, and then by the fairway and/or rough. This longer grass surrounding the green is known as the "fringe" and is designed to slow and stop balls rolling along the green from an approach shot or errant putt, preventing them from exiting the green. Though putting strokes can be made on it, the higher grass can interfere with the path of the ball, so players often choose to use a lofted club such as an iron to make a "chip shot" or a "bump and run", where the ball carries in the air for a few yards and then rolls along the green like a normal putt. The grass of the putting green (more commonly just "green") is cut very short so that a ball can roll for a long distance. The most common types of greens for cold winter, but warmer summer regions (i.e., not extremely warm, as in the Southern and Southwestern United States) are bent grass greens. A green may consist of a thin carpet so that bad weather is not allowed to become a serious factor in maintaining the course. These are considered the best greens because they may be cut to an extremely low height, and because they may be grown from seed. Bent grass does not have grain, which makes it superior as a putting surface. However, bent grass may become infested with "poa annua", a costly and time-consuming weed. Augusta National is one of many golf courses to use this type of green. The original design of Augusta National did not include bent grass greens, but in the 1980s the controversial decision was made to convert the greens from Bermuda to bent grass. This has affected the speed and playing of Augusta National. Many other golf courses subsequently made the decision to change from Bermuda to bent grass when they observed increased business at courses that had already changed over.