You can remove mud by first letting it dry thoroughly and brushing off as much as possible. Then you can rub the stain with Murphy´s Oil Soap, leave for 15 minutes, and rinse with cold water.
Or, instead of the Murphy´s Oil Soap, you could use a solution of 1 tablespoon borax in a cup of water. If the spot persists, use an enzyme presoak, or soak the item in a gallon of water to which you´ve added a cup of ammonia (or use bleach if the items are white).
