How to summon any zombies using the cheat engine?

Change your game mode to I, Zombie by checking the ID of your current game mode. For convenience, I'll use 43 as zen garden and 50 for Tree of Wisdom. Go to your zen garden, type 43 in the value bar and do a scan. Then go to the tree and input 50 and scan again. You should have one address in the table on the left (if not, repeat the process). Double-click that address. Then, go onto any level and pick your plants. Change game mode value to 63 - 70 by pressing Enter with the address selected at the south table. You should be in the I, Zombie game mode. Drag a plant (seed packets don't change) and it should turn into a zombie.