I used the same technique for the fence, with an additional extruded mesh from a selection of, theoretically, the most exposed polygons to the snow (Fig.09).
Most of the small vegetation was grabbed from older projects. The tall grass was just painted on the ground using the script Advanced Painter (Fig.10).
For the midground and background I scattered some long grass, billboard trees and bushes. It's a fast process, but it's worth looking at the reference pictures as much as needed and to try to have a global view of the result at all times to keep the overall consistency (Fig.11).
Texturing / Shaders
The snow material is a simple white standard material. I did some tests using an Arch and Design material with sub-surface scattering, but it increased the render time without really improving the look of the snow (although I did use A&D materials but only for objects with opacity maps, as A&D's "cutout" works better with mental ray than "opacity" in the standard material).
I guess with this type of lighting (sunset with a low and relatively dim light), the modeling is more important than the shader to make it look believable.
Also, using a simple shader was much easier to manage than a complex one. Indeed, as almost all of the objects had at least one snow material on them, they had to look exactly the same (Fig.12).
I was not quite satisfied with the snow covering the pine trees in the foreground. There was clearly a lack of details compared to the scale of the trees. So after testing a couple of possible solutions (I tried to completely remodel the snow using a new selection of leaves and some tweaking in the Blobmesh parameters), the best way I found was to use a Landscape shader in the Opacity slot, so when rendering we see only the upper part of the mesh.
Another trick to simulate a snow layer on the trees was to bake a set of lights placed on top of each source tree (using Render To Texture). The resulting black and white maps were used as masks in the leaf materials (Fig.13).