Are you poor in the sense that you don't have money to buy those shiny upgrades for your plants? Are you constantly having your brains eaten because you don't have the money for Wall-nut Repair? I have the solution! Follow these steps and you can make money faster!
Step 1: Get the Watering Can on level 5-4. Reason: Unlocks Zen Garden
Step 2: Get some plants. Reason: They Drop Coins.
Step 3: Water, Fertilize and make happy. Reason: They can be fed chocolate only of they are fully grown and happy.
Step 4: Amass 10 Chocolate. Reason: Can be fed to Stinky and Plants.
Step 5: Buy Stinky the Snail. Reason: Used if going AFK and can collect Coins faster.
Step 6: Feed Stinky Chocolate (Must have at least 3 Happy Plants). Reason: Stinky Moves Faster and Stays awake longer
Step 7: Feed 3 Plants Chocolate at a time. Wait until they run out of chocolate power and repeat. Reason: Plants make coins faster and will make the most out of Feeding Stinky Chocolate.
Result: Between Step 6 and Step 7 you make about 4k coins.
Question: What is the best plant upgrade?