Quarter and core cabbage. Slice each quarter into 1-inch strips; place in a large bowl and add carrots, radishes, scallions, and salt. Toss to combine and set aside. 

Place ginger, garlic, and chili flakes in a food processor and blend until finely ground. Scrape sides and blend again. Add to bowl of vegetables and use your hands to mix thoroughly. Continue mixing and massaging vegetables for a few minutes until they become juicy and start to soften. (At this point, I always taste a little to make sure it’s just a little saltier than I want the end result to be.) 

Add a handful of vegetables to two wide-mouth jars or a crock, and pound down firmly with your fist to release any air pockets. Repeat with remaining vegetables, a handful at a time, then divide any remaining liquid from the bowl between jars, or pour it into the crock. The surface should be covered with liquid; if not, continue pushing the vegetables down until liquid rises. Press any pieces of cabbage down from the sides of the crock or jars so they are submerged as well. If you’re using two jars, fill two smaller jars or bottles with water and place them on the surface of the vegetables as a weight to keep them below the liquid. If you’re using a crock, use a small plate to hold the vegetables down and place a weight on top of the plate. Cover with a cloth to keep dust and bugs out and place in a well-ventilated, cool area. Ferment for five to seven days or for up to ten days or longer.

Taste the kimchi after five days and then every day until the flavor is to your liking, then cover jars with a lid or transfer from crock into jars and store in the fridge. It will keep for months, and the flavor will continue to develop and strengthen over time, and the vegetables will soften.