When you evaluate a golf green that you're going to play, you need to consider the break and the grain of the course. The break is the amount a putt moves from right to left, or left to right, on a green. The grass of the course can affect the ball's break. The grain of grass refers to when grass grows in a particular direction.
Reading the break of a golf course
Slope, topographical features such as water and mountains, the grain of the grass, and (perhaps most important) how hard you hit the ball dictate the break.
First, find the natural slope of the terrain:
If there are mountains nearby, finding the natural slope is easy. The slope on every green is going to be “from” the mountain (unless, of course, a particularly humorless architect has decided to bank some holes toward the mountain).
If the course is relatively flat, go find the pro or course superintendent, and ask about the area’s lowest point. This point can be 5 miles away or 20 — it doesn’t matter. Find out where that point is and take advantage of gravity.
After you know the lowest point, look at each green in detail. If you’re on an older course, the greens probably slope from back to front because of drainage. Greens nowadays have more humps and undulations than ever and are surrounded by more bunkers. And the sand tells a tale: Most courses are designed so that water runs past a bunker and not into it. Take that insight into account when you line up a putt.
Reading a golf course's grain
Putts downgrain (in the same direction the grass is growing) go faster than putts into the grain (in the opposite direction from the grass growth). The grain of a course, of course, has an effect on where you have to aim a putt.
Look at the cup to find out which way the grass is growing. Especially in the afternoon, you may see a ragged half and a smooth, or sharp, half on the lip of the cup — that shows the direction in which the grass is growing. The ragged look is caused by the grass’s tendency to grow and fray. If you can’t tell either way, go to the fringe (the edge of the green). The grass on the fringe is longer, so you can usually see the direction of the grain right away.
When dealing with grasses, an architect tries to use the thinnest possible blade, given the climate, and then tries to get that grass to grow straight up to eliminate grain.