My beard grows quickly.
"Weeds grow," is Japanese Internet slang used when you think something's funny. It started because "w" (lol) looks like weeds.
Do mushrooms grow in places like this?
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. Remember how 生きる means "to live?" Well this is what happens right after it starts to live. It begins to grow!
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
When something starts to grow it also learns to laugh. Imagine a little plant growing out of the ground laughing. "Ha (は) ha ha ha!" it says, as it sprouts out of the ground.