“Valentine” opens with the speaker’s explicit rejection of typical Valentine’s Day fodder. The speaker chooses to call out hearts and roses, drawing from a pool of the most iconic, universal symbols of love. As a result, other symbols and related images begin to form in the reader’s head—candles, chocolates, wedding vows, The Bachelor franchise, and so on. As the speaker refutes them throughout the poem, these images will come to represent overly romanticized, fraudulent narratives about love. The speaker sets up this symbolism in this initial remark, even as the alliteration of "red rose" is guttural, almost like a growl, and lends the line a harsh tone.
The speaker then juxtaposes this clichéd representation of love with a much less sentimental image:
I give you an onion.
The stanza break that separates lines 1 and 2 reflects the distance between how love is presented and the speaker’s reality. The end-stops that punctuate these opening statements make the speaker come across as direct and confident. The speaker resists the flowery language usually associated with love poems, greeting cards, etc.
And by introducing the onion as an alternative to cheesy representations of love, the speaker sets up the poem’s overarching conceit: an onion as the proper symbol for love.
Finally, line 2 introduces apostrophe, as it becomes clear that the speaker is addressing a silent party. This silent party is the speaker's lover. Apostrophe increases the authenticity of the speaker because the speaker is shown interacting with someone important to them. Therefore, it also heightens the poem’s emotional stakes.