After you’ve removed excess dirt and grass, you should pre-treat your grass stain for the best removal. Pretreat by dabbing a 50/50 mixture of warm water and white vinegar. Saturate the stain well to ensure deep penetration by the vinegar. Allow the watered down vinegar to sit for five minutes. Never use fruit vinegar for stain treatment. Only use plain white vinegar. After your vinegar solution has sat on the clothing item for five minutes, apply laundry detergent directly to the stain. If available, use a detergent that has bleach. Bleach contains enzymes which help break down grain stains. Using powder detergent? Try mixing a dash of water into the powder to make it paste-like, then spread over the stain. Once you’ve applied the detergent, massage the stain. You want to massage gently, as to not ruin the clothing, but firmly, to ensure you get deep into the stain. The longer you massage the more effective the treatment is likely to be. After massaging for several minutes, allow the detergent to sit. Once the stain has sat for 10-15 minutes, give it a rinse with cold water. Check to see if the stain has been removed. It should be significantly fainter, if not completely removed. If the stain isn’t banished, you can safely repeat the process with water, vinegar, and detergent until the garment is stain-free.
Pretreat the stain. Apply detergent directly. Massage the stain. Rinse and check.