Large paintings of grand vistas are a good test for color mixing skill. Oil paint provides many pathways to mixing green. I use some premixed greens and have learned others. One of my choices is black and yellow to get olive and taming a hot green with purples.
Watershed has a wide variety of mixtures of which these two examples are a part. Another thing I did was start on a burnt Sienna ground so right away I’m building contrast between a red underpainting and my green mixtures.