Just a slight caution first... only use bull kelp that has washed ashore, never harvest live ones.
Pickling brine for kelp
2 cups white vinegar
2/3 cup water
1 cup granulated sugar
4 tablespoons pickling spices
1 long firm fresh bull kelp
1 large onion, thinly sliced
1 garlic clove, minced (1 clove per jar)
1 teaspoon lemon juice (1 tsp. per jar)
1 Go beach combing locally (hopefully you’re in an area without lots of water pollution, as I wouldn’t use kelp from a polluted area – check with local authorities to find out, first) and find a freshly-beached bull kelp, making sure it’s firm and fresh. Get 1 or 2 glass jars with lids and make sure they’re well washed.
2 Cut off the hollow portion of the kelp (discarding the bulb) and wash it well in fresh water, making sure to remove any/all sand and detritus.
3 Cut it into 1/2-inch rings and rinse in fresh water again, draining it in a colander.
4 Combine the brine ingredients in a saucepan and bring to a boil. Let boil for one minute, then remove from heat.
5 Place the kelp rings into glass jars and add slices of onion, a minced clove of garlic, and 1 teaspoon of lemon juice per jar.
6 Add the hot brine to the jar(s) then refrigerate for at least 48 hours before serving.