Canning method
Prepare the brine by mixing the vinegar, water, and salt in a large pot. Bring to a boil and keep hot.
In the bottom of each hot pint jar, add 1 to 2 teaspoons each of dill, garlic, and mustard seed. Pack kelp slices or rings into the jar. When half full, add more dill, then finish packing tightly, leaving 1/2-inch headspace.
Pour hot brine over the kelp, leaving 1/2-inch headspace. Remove air bubbles, readjust headspace if needed, wipe the rim, and apply the lid and ring.
Processing: Process pint or smaller jars for 11 minutes in a boiling-water canner. Yield: about 6 pints.