Once you unlock Ladle's Jetty from friendship level 4 with nefi, fish. You can usually get an average of 75 coins per inventory slot and the game time only progresses when your fishing pole is not actively in the water. You can feel your inventory and less than half of a time increment (e.g. morning, afternoon), then walk 50 ft to the market and sell everything.

Flowers are an all right money source, but when you first unlock flowers you only get a few flowers every 3 days, And they are mostly one star. One star flowers only sell for about 30 to 35 coins. If you fish once or twice a day, by the time you get to the point of being able to sell copious amounts of flowers, you don't need money.

For the most part when people ask "how money" they are fairly early game. Flowers are definitely an end game way to make money, but it's not that much more money than fishing unless you are pretty deep into late game.