In grass as with just about any other feature I paint I look for the tool that will best serve the purpose. Now i carry on about my pastry brush for a very good reason-it works! And not just for skies and large areas but for smaller features-like grass. See the trick is to reshape it so it can perform the function I want. Now go and look at the grass in snow and work out the mechanics of it as a subject. It is spiky, long, thin and generally brown to yellow in color. So if i reshape the flat bristle of the pastry brush so they separate and have their own individual space and are still springy they should be able to gather paint then deposit it.
Now I repeat this whereever I want grass. Then with the little liner brush I go to work defining these individual strokes making them both darker here and there and lighter.
See how easy this is. While I was doing this painting I was also filming how to paint a similar winter scene and demonstated exactly how I do this and the other elements that go to make up such a scene. In that demonstation I separated each element and dealt with each so that others can see exactly and precisely my technique. And of course it is all in high definition which is the ultimate in true to life imaging. So if you really want an eyeful take a look at this when it eventually surfaces. Its called painting a Winter Landscape and it is the You Can Paint site which will be launched in a month or so and contains all my instructional material.