1.Cut off the root end of each 4 pounds yeolmu if the root is thin and not usable. Otherwise, cut the thin end of the root and scrape off the impurities with a small knife. Trim off any bad leafy stems, and cut the greens into about 3-inch long pieces. Transfer to a large bowl.
2.Fill the bowl of greens with water. Let them sit in the water for about for the greens to release any dirt. Then, wash the greens a couple of times by gently shaking with your hands in the water. Drain.
3.Dissolve 6 tbsp kosher salt in 4 cups water in a small bowl. Placing a handful of the greens back in the large bowl, sprinkle with some salt water. Repeat the process until all the radish greens are placed in the bowl.
4.Let the vegetables sit for until they become slightly flexible. Flip them over once or twice while salting.
5.Meanwhile, mix 2 tbsp flour well with 2 cups water, and boil over medium heat, stirring, to make the flour paste. Cool.
6.Coarsely blend the 6 fresh red chili peppers, 10 cloves garlic, 2 inch ginger, and 0.25 cup salted shrimp together with 0.5 cup water in a blender. Combine with the 0.25 cup fish sauce, 3 tbsp gochugaru, 1 tbsp sugar, and flour paste.
7.Gently rinse the salted radish greens and cabbages separately in cold water, and drain well.
8.Place the radish greens and cabbages in 3 to 4 batches in the same large bowl, pouring in some seasoning mix each time. Add the 5 scallions and 0.5 large onion. Toss everything very lightly by hand (use kitchen gloves), until everything is evenly coated with the seasoning.
9.Store in an airtight container or jar (about 1 gallon size). Leave it out at room temperature for a few hours before storing in the fridge. You can start eating kimchi any time, but it will taste best after a few days in the fridge.