"Green Grow the Rushes, O", also known as "The Twelve Prophets", "The Carol of the Twelve Numbers", "The Teaching Song", "The Dilly Song" or "The Ten Commandments" is an English folk song (Roud #133) that is widely known. It is sometimes sung as a Christmas carol. The song occurs in many variants, collected by musicologists including Sabine Baring-Gould and Cecil Sharp from the west of England at the start of the twentieth century. The stanzas are much corrupted and often obscure but the references are generally agreed to be both biblical and astronomical. Cecil Sharp noted in his 1916 One Hundred English Folksongs that the words are "so corrupt, indeed, that in some cases we can do little more than guess at their original meaning".
The twelve stanzas may be interpreted as follows:
Twelve for the twelve Apostles the twelve Apostles of Jesus. Sharp states that there were no variants of this line
Eleven for the eleven who went to heaven the eleven Apostles who remained faithful (minus Judas Iscariot)
Ten for the ten commandments the ten commandments given to Moses
Nine for the nine bright shiners may be an astronomical reference: the Sun, Moon and five planets known before 1781 yields seven and to this may be added the sphere of the fixed stars and the Empyrean (the highest part of heaven) or it may refer to the nine orders of angels
Eight for the April Rainers the Hyades star cluster, called the "rainy Hyades" in classical times and rising with the sun in April; the Greeks thought of the Hyades as inaugurating the April rains
Seven for the seven stars in the sky the Seven Sisters, the Pleiades star cluster
Six for the six proud walkers may be a corruption of 'six proud waters', a reference to the six jars of water that Jesus turned into wine at the wedding feast at Cana of Galilee, (John 2:6)
Five for the symbols at your door could mean the mezuzah, which contains a section of the Torah and is inscribed with symbols. It may also allude to the practice of putting a pentagram at the door of a house to ward off witches and evil spirits in the late Middle Ages and the Early Modern period.
Four for the Gospel makers the four Evangelists, Mathew, Mark, Luke and John
Three, three, the rivals may be a corruption of "Riders", "Arrivals", or "Wisers", referring to the three Magi of the Nativity
Two, two, the lily-white boys clothed all in green, O may refer to the story of the Transfiguration of Jesus where Moses and Elijah appear with Jesus in clothes of 'dazzling white'. Sharp cites Baring-Gould's suggestion of an astronomical mnemonic, the Gemini twins (Castor and Pollux) or "signs for Spring". William Winwood Reade implies that the stanza refers to priests who performed sacrifices for the Druids. Normally they would be dressed in white but their sacerdotal robes would be green.
One is one and all alone appears to refer to God

The spiritual "Children, Go Where I Send Thee" has a similar format, counting down from ten or twelve biblical references. Of course for most of us "The Twelve Days of Christmas" is probably the best known cumulative song.
"Echad Mi Yodea" ("Who Knows One?"), a Hebrew song sung at the end of the Jewish Passover seder, has a very similar structure, counting up to thirteen using biblical and religious references.
It was printed by Sharp as "The Ten Commandments", Randolph as "The Twelve Apostles", Abrahams/Foss as "I'll Sing You One Ho!", Karpeles as "The Twelve Apostles" and Silber as "Green Grow the Rushes".
It was printed in Robert Chambers' The Popular Rhymes of Scotland (1870), Enid Porter's The Folklore of East Anglia (1974) and others. It appears as #133 in the Roud Folk Song Index.
It was recorded by Noel Sing We Clear on The Second Nowell (1981).
It was set by Benjamin Britten (as "The Twelve Apostles") in 1962 for the London Boy Singers.
There is a recording by Philip Langridge and the Wenhaston Boys Choir on the Naxos English Song Series.