I’m not sure I understand exactly what you’re trying to accomplish, but if you’re trying to mask out blades of grass that cut cut off abruptly at the edge of the image…
The quick selection tool in Photoshop won’t do a great job isolating the thin blades of grass around the edges, but it might get a lot of them, and even if it cuts many of the blades in half, that may look perfectly fine depending on what you’re trying to do. You can obviously refine the edge of the quick selection as well, and try the auto-enhance option for that tool.
From there you could use the pen tool to add or subtract from the selection and isolate individual blades of grass you really want in or out of the mask that the quick selection didn’t get (this would be pretty painstaking for an image like this, but it gives you a lot of control).
You can also zoom in really close and reduce the quick selection tool brush size very small and try to add/subtract from the selection painting along individual blades of grass; the quick select tool becomes more precise this way.