Easy thing. Since alpha applied textures cannot be z-sorted the model's faces are drawn in the order the model is saved (face1, face2, ...).

a) Use the vegetation material from the wiki (which removes alpha transparency but corrects z-sorting)

b) create your model in a way that the front faces are created at the end. This one's tricky and not always possible. To work around this problem:

c) split your model up in multiple models.