Treat visible mold stains with laundry stain remover according to the label's directions. Most often, these directions instruct to spray, gently rub the spray into the fabric, then allow to sit for 10 minutes.
Pile the quilt into the washing machine loosely so water can easily wash around it.
Pour 1 cup vinegar into the machine then run the water. Allow water to fill, then stop the machine. Allow the quilt to soak in the vinegar water for two hours.
Set the washer to the most gentle cycle, usually labeled as either "Hand Wash" or "Delicate."
Start the machine again and continue the washing process.
Lift the quilt gently from the washer when the cycle has completed and put it in the laundry basket.
Carry the laundry basket and both sheets outdoors.
Spread one sheet onto the ground, a patio, or other flat surface.
Gently spread the quilt on top of the sheet.
Put the second sheet on top of the quilt to protect it from sun bleaching, insects and animals that might litter it.
Allow the quilt to dry outside all day. Return it to dry the next day if needed.