Canción del Jinete" Federico García Lorca identifies blood with flowers. He is not alone there: during the month of november, it is traditional in English-speaking countries to wear a poppy in remembrance of the soldiers fallen in the great World Wars and other conflicts of last century.
During the First World War there was intense fighting in Flanders, (west Belgium). The battlefields were devastated and covered in mud and dirt. People died and so did plants and trees. But when spring came, red poppies flowered and brought hope to the soldiers who had survived the winter. Their red colour could be seen as a symbol of the blood of the dead, and their germination was also a symbol of the will to live on.
John McCrae wrote his poem "In Flanders Fields" in 1915, where he speaks of the poppies growing in the battlefield. And Moina Michael replied with "We Shall Keep the Faith" in 1918, promising to wear a poppy in honour of their dead. The tradition had began.
I would recommend you to read both poems and pray for peace.