Down by the Salley Gardens, words by William Butler Yeats, published in 1889.

Down by the salley gardens my love and I did meet;
She passed the salley gardens with little snow-white feet.
She bid me take love easy, as the leaves grow on the tree;
But I, being young and foolish, with her would not agree.

In a field by the river my love and I did stand,
And on my leaning shoulder she laid her snow-white hand.
She bid me take life easy, as the grass grows on the weirs;
But I was young and foolish, and now am full of tears.

It may derive from The Rambling Boys of Pleasure, which contains the following verse;

It was down by Sally's Garden one evening late I took my way.
'Twas there I spied this pretty little girl, and those words to me sure she did say.
She advised me to take love easy, as the leaves grew on the tree.
But I was young and foolish, with my darling could not agree.

Willows, sallows, and osiers form the genus Salix - hence the salley gardens.