This is a 1972 essay by Alice Walker. In it, she draws upon the writings of Jean Toomer who, in the post-Reconstruction South, witnessed a generation of black women who had seemingly gone mad, become "Saints" who sang "lullabies to ghosts" and went through their lives without fulfillment. Walker's interpretation is that this was not, as Toomer saw it, because they were unusually "vacant," having been beaten down by their difficult lives. On the contrary, she sees them as "Creators" and "Artists" whose spirituality was so deep and unwanted that they went insane because of an inability to express themselves. Unable to release their creativity, they went mad.

Walker poses the question to the reader: what happened to geniuses who were black women in the time of slavery? For a long time, as Walker points out, black people were forbidden to read or write and had no capacity to express themselves through physical artistry. Many, such as Bessie Smith, Billie Holiday, and Nina Simone, expressed themselves through singing, a later evidence, Walker says, of the gift which was stifled in black women of earlier generations. For many black women, singing in church was the only expression of their deep creativity permitted to them.

According to Walker, how did African American women maintain their "creative spirit"?

The original question had to be edited.  I would suggest that Walker's argument is that the "creative spirit" within so many African- American women is left for us to recognize as part of their being.  Walker's primary point is that so many women of color in an American social setting that was predicated upon marginalization possessed unique talents and abilities.  Their ability to "Comb the goddess' hair" was such a part of their being that it came out in everything they did.  

The Smithsonian quilt done by an "Anonymous" woman of color was one way in which this "creative spirit" was evident.  Walker makes it clear that the creative spirit was so powerful in this woman that it manifested itself in the ability to make a quilt.  Walker suggests that the same "radiance" is evident in how her mother plants and tends to her garden.  The ability to see her "creative spirit" is manifested in her gardening abilities.  At the same time, the storytelling ability that Walker's mother possesses is in her own narrative capacity, reflecting another way in which the "creative spirit" is evident.  The "creative spirit" is intrinsic to these women and Walker's primary motivation is to implore the reader to recognize that those in the past possessed this capacity:

And perhaps in Africa over 200 years ago, there was just such a mother; perhaps she painted vivid and daring decorations in oranges and yellows and greens on the walls of her hut; perhaps she sang in a voice like Roberta Flack's - sweetly over the compounds of her village; perhaps she wove the most stunning mats or told the most ingenious stories of all the village storytellers. Perhaps she was herself a poet - though only her daughter's name is signed to the poems that we know.

This is where Walker is most passionate about how women of color, particularly African- American women, maintained the "creative spirit" intrinsic to their very being in a society that left little room for its articulation and praise.