Japanese Indigo (Polygonum tinctorium) from which blue fabric dye is extracted is a leafy plant which thrives in hot, sunny, humid climates. This made blue dye readily available to the peasant class who grew and used it to dye their handwoven hemp and cotton cloth.

Later, when manufactured cotton cloth became available, the peasant class continued to use indigo to over dye their sashiko stitched garments and bedding. The indigo strengthened the cloth, and no doubt gave coherence to the pieced and patched garments and household linens.