Once you have the Zen Garden, water the plants until they don't need anything else. After that, change the Date on your PC to another day. As soon as you do, the plants will need water again. Repeat this -- buy new plants, grow them to full size, sell and repeat to earn money.
This also works to get Marigolds in Crazy Dave's shop when they are out of stock. You can fill up your Zen Garden and make all the money you need. You don't even have to close out of the game.
Play Slot Machine for Extra Coins and Diamonds:
1) Set up your defenses around the slot machine. Try for one row of wallnuts on the right side, one or two rows of sunflowers on the left, and fill everything else with pea and snow pea shooters.
2) Protect the lawn mowers. Each are worth a Gold Coin at the end of the game, so don't let them mow the zombies.
3) Stop collecting sun around 1900 sun points. At this point, the garden should be full, so getting the extra 100 points to win should be easy. Just collect enough sun to offset the slot machine.
4) Keep the slot machine spinning! It will randomly drop one or three gems as long the patience lasts.
5) If the Zombies get close to the mowers, end the game. Just collect the sun lying on the field to end the game.
Milking Walnut Bowling for coins:
Here's how to make Walnut Bowling more profitable:
1) Protect the Lawnmowers -- Each Mower is worth one gold coin ($250).
2) Line up shots off the front runner. After the first zombie is hit, each additional zombie strike generates coins.
3) Create a front runner where none exists! Pole vaulting zombies run fast until they vault over a nut, and the newspaper zombie runs fast after getting the paper destroyed by a nut. Just let them run a little bit down the lawn before sending a nut their way.
4) Just because you have nuts does not mean you have to use them. This is where "Nerves of Steel" comes into play. When there are a few zombies ambling down the lawn without a clear ricochet shot, wait a little bit to see if more of their friends will step out to play. They can always be killed once they cross the red line.
5) Remember how many nuts it takes to kill a zombie; this is important when the cross the red line. Use one nut for regular zombies, three for bucket wearing zombies, and two for the rest.
6) Reserve the exploding nuts. Try not to use those nuts unless a mob crosses the line, or there are not enough nuts or room to clear out a hard to kill zombie. Use the regular walnuts for the zombies that have not reached the red line.
7) Don't use exploding nuts to kill pole vaulting zombies directly. Pole vaulting zombies only jump obstacles in their own lane. A pole vaulting zombie who has not vaulted yet will safely jump over explosions or nuts in their own lane; so find a neighbor in the next lane and time the nut to hit when the pole vaulting zombie gets close to the neighbor.
Switch Locked Seeds:
Tired of being stuck with the crappy cards Crazy Dave makes you have? All you have to do is exit the game and restart it and the 3 cards will be changed to something else.
Unlock Silver Trophy:
When you complete Adventure mode you will unlock the Silver trophy.