Drink to me only with thine eyes,
And I will pledge with mine;
Or leave a kiss but in the cup,
And I'll not look for wine.
The thirst that from the soul doth rise
Doth ask a drink divine;
But might I of Jove's nectar sup,
I would not change for thine.
I sent thee late a rosy wreath,
Not so much honouring thee
As giving it a hope, that there
It could not withered be.
But thou thereon didst only breathe,
And sent'st it back to me;
Since when it grows, and smells, I swear,
The drinking metaphor is changed to one of flowers and the ‘wreath’ to symbolise his love. He sends it, not so much to honour her, but to give the flowers ‘hope’ that her divine effect will preserve them foreover. 
 
 In other words, the speaker views Celia as some sort of enchanted figure that can keep things alive that will normally wither and die. 
 A wreath, a circle of flowers, could symbolise everlasting love.  However, a ‘wreath’ also has associations with death. It could be that the speaker suspects all isn’t well with the relationship.
Song To Celia