This past Friday, March 26th, was Viernes de Dolores, the Friday of Sorrows, which marks the beginning of Easter Week, or Holy Week. The day commemorates the seven sorrows of the mother of Christ. Temporary altars and displays are set up in the streets, usually featuring an image or statue of Nuestra Señora de los Dolores surrounded by flowers, and a variety of traditional items: candles, oranges, bowls of colored water, corn seedlings, and chia sprouts. According to this article, the chia seeds are blessed at the beginning of Lent.
Sprouted sage seeds blessed on February 2, have also long been associated with the celebration of Our Lady of Sorrows. Growing greens remind the viewer of the resurrection and renewal of life. These sprouting sage seeds are also known as chia, the seeds traditionally sprouted in the grooves of clay animals, figures and pots.
Ron Mader of Planeta has documented this use of chia pets in Oaxaca.