The analogy is "Growing a garden is like putting money in the bank".
An analogy is a literary device that consists in establishing a comparison between two things from different nature. It is used to explain something by means of a simplification. In the sentence "Growing a garden is like putting money in the bank", "is like" is what establishes the point of comparison. Moreover, analogies is different from metaphors and similes because analogies are also related to a logical arguments; however, they are mainly used in poetry.