Wheatgrass extract is a powerful hemostatic agent - it stops bleeding from open wounds, deep-seated bleeding in muscles and from a "blood nose".
Apply two or three drops of wheatgrass extract inside or over the bleeding nostril with a cotton bud/Q-tip. Then, pinch the nose with finger and thumb and breathe through the mouth. Bleeding will stop in about five minutes. If it persists, you should seek medical assistance.