Green reading is an art unto itself and sometimes there is a little more to it than just reading the slopes and contours of the putting green. Apart from the natural slopes and contours of the putting green, there are other factors that you need to take into consideration when green reading and one of these factors which is highly significant is the grain.
The grain is the direction in which the individual blades of grass grow on the putting green and there are 2 main types of grass that are used to surface putting greens, Bent grass and Bermuda grass.
Bent grass is easier to grow and maintain in cooler climates, the blades of grass are light and thinner, which makes them tend to grow more vertically. Bent grass is easier to cut short, so you will usually find that putting greens with this type of grass will be faster have little or no grain.
Bermuda grass on the other hand prefers warmer climates and has much thicker, heavier blades which makes it harder to cut short. Due to its heavier weight the grass grows horizontally along the surface of the putting green creating a considerable grain.
This grain has a significant impact on the pace and direction in which the ball will travel, so needs to be respected when green reading. If you are putting into the grain, the resistance of the blades of grass will act like a brake and slow your putts down considerably.
Putting with the grain has the opposite effect, can almost feel like an ice rink the ball just seems to keep going. When faced with side hill putts, if the grain is going down hill you will need to allow for more break and visa versa if the grain is growing up hill.