Place the julienned parsnips little by little in your fermentation jar, pounding them vigorously and sprinkling some of the sea salt as you go.
Make sure the mixture fills the jar up to no more than 1 inch below the top (because of the expansion), adding more if needed, and that the extracted water covers the vegetables entirely. If not, create a brine of 2 tablespoons sea salt to 4 cups water and add it to the mix.
Press the vegetables and keep them under the brine by placing a plate or a lid on top weighted down by a rock or a jug of water. Cover with a clean towel if needed to keep out fruit flies.
Place the fermentation jar in a warm spot in your kitchen and allow the parsnips to ferment for 7 to 10 days.
Check on it from time to time to be sure that the brine covers the vegetables and to remove any mold that may form on the surface.