Along with angles, outdoor footing is the other most often ignored facet of outdoor model horse photography. The fault lies in scale - the relative size of the footing compared to the model horse. I'll do a full post on scale later in time, so hang tight.
This post will cover the two most commonly out of scale footing types: grass and snow. In general, I try to keep footing as high as the horse's fetlock at most. Snow can be a little higher, but generally anything above that height looks out of scale in proportion to the horse.
Admittedly, grass is a very hard type of footing to perfect. Unfortunately, our lawn mover broke down this summer, so currently our backyard is somewhat of a jungle and I don't have a good example of an in-scale grass footing photo. Generally, it is best to take photos with freshly-cut grass to keep it as in scale as possible. Some try to pass off this grass as "tall grass," but in reality tall grass and normal grass look nothing like each other. Examine the two photos below:
Photo #2 is unfortunately artificial grass for reasons as stated above, but much more in scale with the horse. It gathers around the hooves only and doesn't extend above the fetlock. The bushes aren't my favorite, but that's beside the point of this post.
Snow is a bit easier to deal with than grass, but still tricky, especially when you have a large amount on the ground. Like grass, you shouldn't let snow get above the fetlocks, but you can fudge with it a bit more than grass. The big idea to keep in mind is that yes, horses can move in higher amounts of snow (within reason, of course) but it might not be as gracefully as the model's pose suggests. Now, examine these two photos:
this video of miniature horses in snow that's chest height.) If this horse were real, his gait would have to be much more exaggerated and strained to get through that much snow.
Photo #2 is a big improvement. The snow could be deeper, but this height is just fine to set the scene. The horse can move easily and he is not constrained by the height of the snow. The bits of grass sticking up are also in scale and are disguised as stray plants that were too long to be covered up by the snow at this point in time.
Snow is also easier to work with than grass because of the fact that you can change the height of it much easier. If it's too high, you can shovel out an area, and if it's too low, you can take some from another area and move it to where you need it.
Remember - it's okay to break up snow and/or create "hoofprints" behind the model; in fact, you probably should do it. Horses don't just magically fall from the sky into a snowbank, you know! They're constantly moving and breaking up the snow around them.