What is meant by 'October blood'?

The phrase 'october blood' is occurred in the last stanza of the poem, Poem in October, by Dylan Thomas which is published in the volume, Deaths and Entrancec in 1946.

         The speaker in his thirtieth birthday, seeing the beauty of hilly area which is full of 'springful larks', 'whistling blackbirds' and 'the sun of October summery', remembers the days of his childhood when "he walked with his mother/Through the parables/ of sunlight/ And the legends of the green chapels." But this days are no longer, he now belongs to the mature age.

       His days have changed so considerably that the town below seems to be besmeared with the red leaves of autumn. The phrase 'October blood' refers to the red-coloured leaves of the trees fallen on the ground. But the poet uses this phrase symbolically. He compares his present stage with the 'October blood' as in this stage, he is departed from the 'blithe country', from 'the other air', from 'the blue altered sky', from the childhood stage. He asserts that his days of "all the gardens/of spring and summer" are now no more. Actually the phrase represents a stage of psychological depression and disillusionment.