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: What do you flourish at? You're an amazing soccer (さか) player who flourishes and prospers no matter where you go to play this wonderful (but not as good as baseball) sport.
I thought this city would be more prosperous.
This used to be a prosperous silver mining town.
There was a village in China flourishing from their production of stimulants.