Prepare your jar and lid by washing in warm, soapy water, and rinsing well. Place your jar rack into a small water bath canner or large pot. Add water to cover the jar and boil for 10 minutes to sterilize. Turn off heat and add the lid to the warm pot to soften.
Rinse garlic scapes and cut into 4-inch pieces to fit in the jar. Discard the top of the flower and tough ends (or toss into a freezer bag and save to use for making stock).
Combine the vinegar, water, and pickling salt in a small pot. Bring to a boil and stir until the salt is dissolved.
Remove the warm jar from the canner, drain, and place on a kitchen towel. Add the mustard seeds, black peppercorn, allspice berry, clove, bay leaf, and red pepper flakes or chili pepper to the jar. Pack the garlic scapes into the jar.
Pour the hot vinegar mixture over the garlic scapes, leaving 1/2 inch of headspace. Remove air bubbles and wipe the rim. Use your magnetic lid lifter to lift the lid out of the warm water, center the lid on the jar, and tighten the screw band until it is fingertip tight.
Place the jar into your water bath canner, adjust the water level so it is 2-inches above the top of the jar. Bring the canner to a boil, and process in a hot water bath for 10 minutes.
Turn off the heat, allow the canner to cool, remove the jar, and place it on a kitchen towel to cool. Check seals and store in a cool, dark location. Allow 2-4 weeks for the garlic scapes to develop their flavor. Once the jar is open, store in the refrigerator for up to 2-weeks. Recipe makes one pint.