Wash and trim garlic scapes, then pack into your jar(s). You can keep them curled or slice to fit standing up.
Combine the peppercorns, mustard seeds, and crushed red chile flakes, then divide between jar(s).
In a medium pot, combine vinegar, water, pickling salt, and sugar. Bring to a boil, stirring to dissolve.
Once fully dissolved, carefully pour hot brine into the jar, leaving about 1/4-inch headspace. (You might not use all of the brine, or you might need extra.) Press a chopstick or wooden dowel against the inside of the jar to remove air bubbles. Place lid on loosely.
Let cool to room temperature, then store in the fridge until ready to serve. For best flavor, wait at least 1 week before eating.
Notes
This recipe will yield approximately 1 16-ounce (pint) jar.
Cook time is for refrigerator pickle. If water bath canning, process for 10 minutes, then remove and let rest for 24 hours before testing seal and storing in the pantry.