Directions

Cut the blossom ends off the cucumbers.
Stir the soak salt into the 4 cups cold water and soak the cucumbers overnight, 8 to 18 hours, holding them under with a weight. In a very warm house, soak them in the refrigerator.
Mix the brine ingredients in a pot, bring to a boil, and simmer until the salt has dissolved.
Split the hot brine between two sterilized 1-quart jars and leave it to cool overnight.
In the morning, drain the cucumbers and fit them into the jars along with the dill, horseradish, and mustard. Hold the pickles under the brine with a weight, leaving at least 1 inch headroom.
Fit on a gas-release lid and keep in a cool, dark place.
The pickles will bubble and ferment for 4 to 5 days. Leave them alone until you are ready to eat them; the flavor is best after at least 1 month.

Notes

Keeps up to a year in a cool, dark place (or up to 6 months); refrigerate once opened. If cucumbers don’t fit under the brine, add a bit more water only (not more salt or vinegar). Sanitize jars for long storage. Don’t use cucumbers with mold or slime; never eat anything that looks or smells bad. A white dusting on pickles and the jar bottom is spent yeast or salt. Safety: room-temperature storage for months is not a tested method; NCHFP/USDA guidance is to refrigerate fully fermented pickles or process them by a tested canning method for shelf storage. Discard if soft, slimy, moldy or off-smelling.