Reserve half of the garlic, ginger and green onion for later in the week. Tie the green onion bundles with twine.
In a slow-cooker, add green onion, garlic and ginger. Fill slow cooker with water, up to 1-inch below rim. Set to cook on high heat at first. When the bone broth comes to a simmer after an hour or so, you'll see lots of scum. Skim and discard. Set slow cooker on low and let the bone broth cook for at least 6 hours.
Use a skimmer to skim the surface of any particles and oil. Season with salt, to taste.
After drinking some of the bone broth, top off the slow cooker with additional fresh water. After 2 days, discard the spent meat and bones, herbs and vegetables. Cooking the bones beyond 2 days may make the soup taste sour, as the bones break down. Add the reserved garlic, onion and green onion (and additional meat/bone if desired). Continue to add additional vegetables, aromatics, dried ingredients (see post above for details) as you wish. Keep the setting on low.