Grass stains combine plant pigments with soil and proteins, so pretreatment usually works better than simply choosing a hotter cycle. Treat the stain before machine drying and follow the fabric label because heat can set what has not yet come out.
Remove dry soil before wetting
Shake or gently brush away loose dry soil without spreading it across the fabric. Starting with wet mud can push particles deeper between the fibers.
Pretreat with a compatible detergent
Apply a small amount of compatible liquid detergent or stain remover and work from the edge toward the center. Let it sit for the label-specified time without allowing the product to dry on the fabric.
Wash at the temperature the garment allows
Use the normal suitable cycle and do not increase temperature just because of the stain. On whites, any whitening product must be compatible with the fiber and label; never mix incompatible chemicals.
Check before tumble drying
If a green or brown shadow remains, repeat pretreatment while the garment is still damp. Dryer heat can make the remaining stain harder to remove later.
Sources
- American Cleaning Institute — Cleaning Tips — Household cleaning methods, product use and dosing, and material compatibility.