The song is about the Bealtaine ritual. It mentions tying ribbons on the Ash and Oak and Birch and Yew and other parts of the ceremonies. Here is a similar verion of the words that were written down in Cornwall in about 1400:
Awake, awake my pretty, prithy maid, Come out your drowsy dream, And step into your dairy hold, And fetch a bowl of cream.
If not a bowl of cream my dear, A cup of meade wot cheer, And we shall meet again in spring, To go Maying another year.
A branch of May I brought you here, While at your keep I stand, 'Tis but a sprout all budded out, The work of Brigit's hand.
My song is done and I must be gone, No longer may I stay, But bless you all, the great and small, And send a joyous May.