Bring a medium pot of salted water to a boil. Wash fiddleheads well and trim the brown ends.
Boil fiddleheads for 10 minutes in the water, then drain well and rinse with cold water.
In a small pot, combine rice wine vinegar, salt and 1/2 cup of water together and bring to a boil. Reduce heat to low and keep hot.
Place 2 sterilized half-pint jars on a clean tea towel. To each jar add 1/4 tsp cumin seed, 1/2 tsp each coriander and peppercorn. Add a clove of garlic and a slice of ginger to each jar.
Pack the cooked fiddleheads into the jars and cover with the hot pickling liquid.
Place the lids on the jars and process in a boiling-water bath for 10 minutes.