Sometimes watercolorists have to think like sculptors. Michaelangelo, when once asked how he could carve a figure out of a block of stone, said, "It's easy. I just carve away everything that is not the figure." In painting, that advice can come in handy. Instead of painting the subject, just paint everything that isn't the subject.
This technique is referred to as painting the negative space. In "Knickercane", study the tree trunk on the left of the mass of trees. After painting an initial wash, I carved out the tree and its branches by painting the space behind the tree.
This painting also helps illustrate problems with large masses of green. Study it for seeing the subtle changes in shades, tints and tones of greens. I never use a green straight from the tube.
I either warm it up or cool it down, trying to mix the colors on the paper to avoid muddying them.