I spent the last few days making some weeds for my post apocalypse. These are bits of plastic plants from various craft stores mounted on styrene plastic bases. The bases are painted a "dirt" yellow, then flocked with a Woodland Scenics mixture, glued with acrylic artist's matte medium.
These are for use with 28mm figs, and most stand between 1-2 inches tall. The taller ones in the second photo stand about 4.5 inches tall.
Generally, these are for mixing in along streams and rivers and whatnot with my more conventional shrubs and bushes, though the frosty green things with the purple seed pods in the last photo have a specific purpose, and will be of some importance in my future games.