Wash jars and lids with soap and water.
Place jars and lids in a pot of water, bring to a boil then reduce heat, cover and simmer for 10 minutes. Drain the water carefully then your jars and lids are ready to use.
Divide bay leaves, peppercorns, dill stems, garlic, and horseradish (optional) into the bottoms of 6 Quart-sized jars. Pack cucumbers tightly into jars.
In a medium pot, combine 8 cups water, 1/3 cup sugar, 6 Tbsp salt, and 6 cups vinegar. Bring pickling juice to a boil then pour over cucumbers leaving 1/2” of space at the top.
Screw the lids on enough to keep a tight seal in place but don't over-tighten them since air bubbles need to be able to escape.
Place jars in a canner or large pot lined with a wire rack at the bottom. Once all of the jars are in the pot, add boiling hot water, to cover jars with 1-2 inches of water. Process/boil for 15 minutes.
Carefully remove jars from the water using a jar lifter and leave at room temperature undisturbed for 12-24 hours. You may hear a pop when the jars fully seal.
After 24 hours, check that the seal has formed by pushing down on the center of the lid - it should not move at all. If the seal does not form, refrigerate pickles and enjoy within 3 months.