Rinse the pickling cucumbers under cold water, scrubbing gently to remove dirt. Slice into ¼-inch thick slices.

Toss cucumber slices and onions with pickling salt in a bowl. Cover with ice and refrigerate for 4 hours.

Rinse the vegetables under cool water to wash away excess salt.

Sanitize jars in a hot water bath and keep them warm.

Combine white vinegar, apple cider vinegar, sugar, and pickling spices in a pot. Heat until boiling.

Add the cucumber and onion slices into the hot brine and return to a boil for 2 minutes.

Pack the hot cucumber and onion mixture into jars with the brine, leaving ½ inch of headspace.

Seal jars tightly and process for 15 minutes in boiling water or refrigerate after cooling.