吾が言の葉の Waga koto no ha no
散りぬるを Chirinuru wo
花の歌とや Hanano uta to ya
人のながめん Hito no nagamen
By the spring wind
My words are blown and scattered
People may see them
The song of flowers
"Koto no ha" (言の葉) literally means "leaves of word" that refers to words in general or a waka poem. In a spring day, flowers, probably cherry blossoms, are blown by the wind and falling. Dōgen's mind is also blown by the spring wind and a waka poem was generated using the leaves of words. This is what "my words are blown and scattered" means. This also means Dōgen does not cling to his words that are scattering.
In Shobogenzo Keiseisanshoku (Sounds of Valley Stream and Colors of Mountian), Dōgen comments on Su Shi's poem that says the sounds of valley stream are voices of Shakyamuni's expounding the Dharma and the colors of the mountains are the pure body of the Buddha. When we are liberated from the five aggregates of attachment (panca upadana skandha), the objects of our sense organs cease to be nama-rupa (the objects of our thoughts and desires). Then, as Dōgen says in the beginning of Genjokoan, we see myriad things as Buddha-dharma.
When Dōgen writes this poem on falling flowers, he is expounding this truth. And yet, common people probably think that his poem is about the admiration of the beauty of the falling flowers as nama-rupa (objects of our sense organs). Snow, moon, and flowers are such common motifs in waka poems that people consider any waka about flowers as hackneyed and not well appreciated.
In The Zen Poetry of Dōgen, Steven Heine offers another possible interpretation. He suggests "the song of flowers" means the song sung by the flowers. When people read Dōgen's poem, they might think the poem is the singing by flowers. It is not a poem written by people observing the flower and write about their beauty as observation from human perspective. This is a very unusual interpretation.