Zarzamora con el tronco gris,
dame un racimo para mí.
Sangre y espinas. Acércate.
Si tú me quieres, yo te querré.
Deja tu fruto de verde y sombra
sobre mi lengua, zarzamora.
Qué largo abrazo te daría
en la penumbra de mis espinas.
Zarzamora ¿dónde vas?
A buscar amores que tú no me das.
A dialogue between two characters. One, a person, another, a plant. Neither speaker is "the poet."
Let's assume that in order to understand the poem, we have to know when the poet wrote it, what he was thinking. Or conversely, that the poem helps us understand the poet's deep psychology. We could come up with something easily. The berry-bush is the sexual / amorous object. The speaker makes his proposal: a branch of berries for him. The bush (the object of desire) answers that the result with be blood and thorns, that he will have a long embrace in her (his) penumbra. Then, at the end, the berry-bush gets up and leaves, to find loves that he (the poem's speaker) cannot give her. Then we could speculate about whether the poem talks about Lorca's inability to be heterosexual, etc...
If we see it as an imitation of a popular, anonymous song, then we don't have to know anything about the author. The speaker becomes the anonymous, generic speaker of the popular anonymous tradition. We can't quite see it that way, because the psychology seems too particular, too Lorquian. Yet the poet has distanced himself from autobiographical content precisely by imitating this popular style.
By the way, it is a beautiful poem. Now I know why I can't leave Lorca behind.