The symbol of cotton stems from the nurturing and temperate climate required for the cotton flower to bloom. Requiring two hundred days without frost to fully mature, the cotton flower must go through a series of stages, from yellow to pink to red before falling away to uncover the fluffy pod within.
In addition, the use of cotton as a material of binding and weaving reflects the bonds that have formed between the still maturing couple and reminds them to recall the wedding vows that started the interweaving of their lives.
In Buddhist wedding ceremonies, a string is used to physically bind the hands of a couple, representing the joining of body-to-body and spirit-to-spirit.
The gift of cotton on the second wedding anniversary reminds the couple of those ties and urges them to reflect upon the connections that first brought them together.
Paraphrased from The Meaning of Wedding Anniversaries by Gretchen Scoble and Ann Field, Chronicle Books LLC, San Francisco, CA, 2004