1. Treat the stains with mineral spirits or acetone; work in a ventilated room. (Test on an inside seam first to be sure the treatment won’t damage the fabric.)
2. Press cheesecloth on the wet spot, then tamp with a soft-bristled brush to remove as much grass pigment as possible. Repeat as needed.
3. Flush the area with rubbing alcohol, tamp with the brush, and let dry. Apply an enzyme detergent (check the label) to remove any residue before laundering.
Martha Stewart Living, May 2014