Question: In Plants vs Zombies, are there strategies that make it more probable to have certain plants (for your Zen Garden)?

How does the game decide which plant is given?

Answer: 
I believe the game hints mention that certain types of plants only appear in certain types of boards or levels.

For aquatic plants, you need to be playing an aquatic level.

For plants for your fungus garden, you need to be playing a night level.
Based on the comment from [Guillaume Coté](https://gaming.stackexchange.com/questions/26034/how-to-obtain-a-specific-plant-for-the-zen-garden/31908?noredirect=1#comment177519_31908), going to add a clear answer

Short answer: **NO**, you can't pick an **specific** plant. But there are someways to get a **specific type** of plant (aquatic, mushrooms ...)

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I once read that: *(lost link)*

* Aquatic levels (pool) increase your chances to get aquatic plants.
* Night levels (night) increase your chances to get mushroom plants.

But the best way to get Zen Garden plants is to play Survival: Endless, as all plants can be obtained in it and it is the level with the greatest number of zombies.