What poem has the line "I could love you as dry roots love rain?"
That line was written by the American poet Carl Sandburg. The line is the opening line from his poem "Offering and Rebuff."
The poem is quite short, but the opening stanza is a beautiful explanation of how much the speaker loves his special someone. Dry roots would crave and yearn for rain. And once they got the moisture, they would absorb it in its entirety. The rain and the roots would essentially become one. That's a fairly good description of what people believe about true love and marriage.
Sandburg continues the image of the speaker's love having/wanting a secure hug/hold. The next line of that stanza tells the reader that his love's embrace would be strong and secure like a tree's grasp is on its leaves during a windy day.
I could hold you
as branches in the wind