Gather fresh plant materials for your dyes. Choose fully-open flowers, plump and ripe berries, large and thick leaves and fibrous roots.
Choose plants with colors much darker than you want your dyes to be. For instance, if you want pink dye, use dark red cherries, fully ripe strawberries or beets. For yellow, try bright orange carrots or turmeric. Try blueberries and grapes for blue or purple and spinach for green. Note that the blossoms, fruit, leaves, stems and roots of one plant may all produce different dye colors. Keep plant parts separate.
Chop up your plants into 1/4-inch pieces. Pour them into a large stew pot along with equal parts apple cider vinegar and water. For instance, if you have one cup of plant material, add one cup each of water and vinegar to the pot.
Bring your dye mixture to a boil on high heat. Turn the heat to medium high and let the dye simmer for an hour or so. Strain out the solid plant materials with a sieve before dyeing clothing.
Soak your natural fiber fabric in apple cider vinegar for 10 minutes before dyeing. This intensifies the color and helps more of the dye soak into the fabric.
Pour your dye into a plastic tub and lower your fabric into it. Allow the fabric to soak for an hour. If the color isn't dark enough, leave it in the dye and check on it every 30 minutes until you achieve the desired color. Note that the color will be lighter when the fabric dries. If you want very dark color, the fabric should look almost black before it's ready.
Fill a clean tub with cool water and dip your dyed fabric in it. Lift the fabric up and wring it out. Repeat five or six times. This bleeds off the extra dye so your color doesn't run later.
Hang your fabric up to air dry. Iron it with a clothing iron on the cotton setting (no steam) to set the color.
Wash your fabric in cold water by itself and hang it up to dry.