Adding a meadow effect to a view is easy to do – just follow the guidance and sample code at GPU Gems. A key to getting a really dense coverage is to make each plane of the billboards very large to cover a large number of plants. Plant these close together at random rotations to generate overlapping planes of planting.
The above strip of plants is placed on a cruciform arrangement as shown here;
and textured here;
The key is to overload the screen with many repetitions of randomly positioned and randomly rotated cruciforms leading to a dense near field of view.