花草 is a collective term meaning "flowers and plants" or "vegetation." It is used when referring to ornamental plants and greenery in general, rather than a specific species.
阳台上的花草长得特别茂盛。
yángtái shàng de huācǎo zhǎng de tèbié màoshèng.
The flowers and plants on the balcony are growing especially lush.
她每天早上都会给花草浇水。
tā měitiān zǎoshang dōu huì gěi huācǎo jiāoshuǐ.
She waters the flowers and plants every morning.
这个小院子里种满了各种花草。
zhège xiǎo yuànzi lǐ zhòngmǎn le gè zhǒng huācǎo.
This small courtyard is filled with all kinds of flowers and plants.