The quest is unlocked after completing the Market Apeel quest.
"The Yiga Clan's latest scheme? To buy up every single mighty banana in all of Hyrule! Needless to say, such a massive shopping spree will cost them an awful lot of rupees..."
"Though their numbers were limited, the Yiga still managed to buy every last mighty banana in all the land. It seems they aspire to start a garden after the clan has returned to its former glory."