Plants make their own food for survival.

Primarily from Sol. 

Sol, our Sun.

And water.

And carbon dioxide.

Fertilizer delivers nutrients for survival as well, but commercially, not naturally. 

Plant food is not the same thing as fertilizer, and vice-versa.

Fertilizers work to enrich the soil, while plants use the nutrients found in the soil, and in the environment, to create their own food.

To put it simply, fertilizers and products that are labeled Plant Food are really just soil additives that contain lots of nutrients.