To make radish kimchi, start off by properly cleaning the radishes. Scrub all the dirt and impurities from the radishes. If the skin is not clean, you can peel off the skin. Thereafter, cut the radishes into 1-inch cubes and place them in a large bowl. 

Once the radishes are cut in cubes and placed in a bowl, sprinkle kosher salt or non-iodized salt over all the cubes and toss them properly to ensure that it is evenly spread. Now let the cubes sit this way for 30-40 minutes so that the radish cubes soften and let out some liquid.  

In the meantime, prepare the seasoning ingredients and keep in a separate bowl. Ensure that they are properly mixed. Let it rest this way for a while till the red pepper flakes get properly dissolved and become pasty in texture. 

Meanwhile, drain the liquid from the radish cubes using a colander. Ensure that you don't rinse the radish cubes as that can adversely affect the flavor of the vegetable. Note that radishes have a lot of water content. During the fermentation process, more water will be released, as a result of which, the kimchi will have a thick gravy. 

Once the radishes are properly drained, place them in a bowl and add the scallions and seasoned ingredients. Mix everything really well, preferably with your hand so that it is evenly coated with the ingredients. Ensure that you are wearing gloves while mixing the ingredients and the radish cubes. You can taste the radish at this point to gauge the taste. It must be a little too salty to taste at this point. You can add the other ingredients at this point if you think it requires so. 

Now take an airtight container and place the radishes in it. Keep pushing them inside the container with your hand so that there are no air pockets between the cubes. Depending on how fast you want your kimchi to ferment and ripen, leave the airtight mason jar out at room temperature. Thereafter, keep it inside the refrigerator. The longer you keep the kimchi inside the fridge, the better it will taste. It is ideal to have it after a week or two of keeping it inside the refrigerator as the flavors will properly mature this way and stay on for longer.