While your cabbage is pickling, make the kimchi broth by blending together your onion, Korean pear, Korean radish, apple, garlic, and ginger, with 1 cup of water. Then, strain the blended ingredients through a mesh strainer into a large container that's large enough to house your cabbage heads (remember, they will shrink considerably in the next several hours). Add 1 quart of cold water to the strained ingredients (you can strain the water together with the blended ingredients, a little bit at a time, as it helps with straining). Mix in 4 to 6 tablespoons of salt to the liquid--it should taste "too salty," but that saltiness will dissipate over time and optimize the fermentation process.
Once you've determined that your cabbage leaves are ready, drain all the salt water and make sure you rinse the cabbage leaves thoroughly in cold water. The general rule is to rinse them each twice. Squeeze out excess liquid and pat them dry as best you can with a kitchen towel. Then, place them, face down, in the large container containing your white kimchi broth. Press down on them to remove any air bubbles.
Add your green onion, whole, directly to your cabbage heads. Ideally, your cabbage heads should be in a container where they are completely submerged or pressed down. If you don't have a container that fits the cabbage heads, add a layer of plastic wrap to the top of the kimchi before closing the lid.
Leave your white kimchi out at room temperature for 3 days. Give your kimchi a taste. If it hasn't fermented as much as you'd like (i.e., because your cabbage leaves are very thick), let it sit at room temperature another day. Afterwards, store in the refrigerator.