This trick uses the same method as discussed in bypassing Lot limit reached trick discussed earlier. When you put your Plants, the more you put, the more Plants at the back will out of range and can only attack if the frontline Plants die. Wouldn’t it be nice if you can stack all Plants in one square area? Upon doing this, your fire power is absolutely focused and you can possible kill Zombies appeared in a single blow.
Plants vs Zombies Adventures secrets: how to stack plants - Method
How to stack Plants in PvZ adventures? As discussed in the Lot limit guide, you need to visit your neighbor to pull this trick. This is not a cheat or hack or anything similar. It is just a tiny loophole discovered accidentally. You can place Plants on neighbors Town when paying them a visit. The Plants will be transferred back to your Town in the exact same location. If you re-visit that neighbor, the Plants should be gone. So, what is the merit of doing this? If you put one Plant in a square area, you cannot put another one at the same place. The case is different if you put in your neighbors Town. There is probably no Plant at your targeted location. After you put a Plant on it and go back, there will be two Plants stacking. Repeat this a few time until your Lot Limit is reached. You can stack different kind of Plants, or same Plant in one spot and they will look like one!
Note that this is obviously a very unfair exploit of the game. It is very likely that the game developer will fix this once it is discovered. Good luck!