The following table provides a quick look at what your static grass would look like in real life.
Weeds and grass in fields vary in length and color. So for a realistic look, get a variety of sizes and colors.
Most model scenes will show something other than a trimmed lawn. So, the larger sizes are appropriate.
To make flowers, choose longer grass. Here is a link to a video that shows how to make flowers with static grass. How To Make Flowers With Static Grass
Get static grass in each of the above sizes by clicking on this link. Static Grass.