The super brush end of a Sketch or Ciao marker is very flexible, and really feels like a brush. With a little flick you can get a perfect tuft of grass. Flick a few times to build your tuft. Practice a bit, since this is a basic brush technique, yet it takes a light hand. Make your motions very quick and light.
It's fine to practice large and small, until your hand can comfortably make these little grassy chunks. Keep your wrist very loose when doing this. Practice making some large clumps and some small tussocks.The trick to making believable grass is to make it irregular. Some blades are short, some are tall, and the colors range from light to dark. Add a few dead blades - see how much more dynamic it looks.
I'm sure that any outdoor picture you work on would benefit from a few tufts of grass and you can always dab in a few rocks for a simple accent as well. Or, use the blender pen and dot in some rocks over a simple light brown groundcover.
For a nice smooth lawn, practice making blades that are all the same length and in a nice row, since a well-manicured lawn is very clean and even. This makes a wonderful ground cover that doesn't detract from the main image. If you want a solid green area under your blades of grass then color the big green area first, then, while it's still wet on your paper, add the individual flecks of grass. That way you won't get the annoying darker spots under your blades like you see on my first lawn example. Add your darker color after you do the light color.
Sky and Grass
When you are adding grass to a picture that you also want sky in, do the sky first, since your grass will overlap the edge of the sky. Sky is usually blue, and grass is usually green, and green is made from blue so if your green overlaps the sky it won't look so bad.
Trying to carefully color sky between tiny blades of grass so you don't bleed the blades out is much harder. Trust me. Just do your sky first and add your grass later. On this picture I got tired of making softly blended skies, so I colored the blue then dabbed on the blender to get the mottled look. See how I made my first layer of grass? Now I add my darker blades over the top of this to get the overall lawn look.