Why does Alice Walker search for her mother's garden?

In Walker's essay, "gardens" are used both literally and metaphorically to examine the ways in which black women have managed to be creative, even in situations in which creativity seemed impossible. 

Her literal example is her description of her mother's garden. Walker was the daughter of Georgia sharecroppers who, in spite of their oppression and impoverished circumstances, expected more for their daughter. Her mother, like most black women in the early-20th century, worked hard to take care of her husband and children and, for survival in the Jim Crow South, to serve white people's economic interests: 

She made all the clothes we wore... She made all the towels and sheets we used. She spent the summers canning vegetables and fruits. She spent the summer making quilts enough to cover all our beds. During the "working" day, she labored beside -- not behind -- my father in the fields. Her day began before sunup, and did not end until late at night.

In the midst of all this work, Walker wonders how her mother had time "to know or care about feeding the creative spirit." Yet she did just that, adorning their home with flowers:

She planted ambitious gardens -- and still does -- with over fifty different varieties of plants that bloom profusely from early March until late November... Whatever she planted grew as if by magic, and her fame as a grower of flowers spread over three counties.

Not only does Walker's mother find a way to be creative with her flowers, she also finds a way to be "ambitious." The expression of ambition was something that was denied to black women in the Jim Crow South. Moreover, that ambition is perennial, expressing itself "profusely" during the year. Walker's mother succeeded in leaving an expression of herself in the soil, in the small plot of land that was granted to her. In an environment that intended to exploit her, then erase her, this is a political statement -- a testament to the perseverance of black women. Eventually, this creativity is recognized, allowing Walker's mother "fame as a grower." 

Another important example that Walker gives is in the tradition of quilting. In the Smithsonian Institution, there hangs a quilt "unlike any other in the world." It is "fanciful, inspired, and yet simple...it portrays the story of the Crucifixion." 

Patchwork quilts had practical use in black homes and were usually made from old, worn pieces of clothing and other fabrics that had fallen into disuse. Because black women could not afford to purchase linens, as white women often could, they had to make their own out of whatever materials they had around. However, in doing something practical, they could also be inventive. The Smithsonian quilt, "made of bits and pieces of worthless rags," ironically has become priceless. It is a testament to the indomitable human spirit.