What's definition of "bank" here? I did some research, and I found that the expression "bank for flowers" is not uncommon. However, I am still not sure of its definition. In some cases, like in "He was buried under a bank of flowers sent by his friends", bank obviously means something like a heap or pile.

However, this doesn't work in some other contexts. For example, the line in the subject refers to naturally growing flowers. So does the poem by Robert Burns ("On a bank of flowers, in a summer day"). Does this mean something like a small hill on which flowers grow?