Espinos translates to "thorns". It's a vivid and somewhat poetic word that isn't as common as everyday vocabulary, making it memorable.
In the song, the artist uses "espinos" metaphorically to describe the pain and hurt that resulted from a failed relationship. He sings, "Pero recogí dolor porque nacieron espinos" (But I harvested pain because thorns were born), illustrating how his efforts to cultivate love led to suffering instead.
Alkilados' "Tierra Mala" is a really relatable song about putting your heart and soul into a relationship, only to realize the other person just isn't feeling it. The singer talks about how he's been nurturing this love since childhood, saying, "Sembré semillas de amor en tu alma desde niño / Las cuidé con ilusión rodeándolas de cariño" [I sowed seeds of love in your soul since childhood / I cared for them with hope, surrounding them with affection].
But despite all his effort, the love never grew. He wonders if he "sembré en tierra mala o no supe sembrar" [sowed in bad soil or didn't know how to sow], but ultimately concludes that the other person is "tierra mala" [bad soil] because the love he dreamed of never blossomed in them. It's a pretty blunt way to say it, especially when he sings, "El amor que yo soñé nunca floreció, en ti" [The love I dreamed of never bloomed, in you]. The song's a great listen for anyone who's ever felt like they gave their all to someone who just couldn't reciprocate.