Add the sliced cucumbers to a very large non-reactive bowl (glass, ceramic, stainless steel). Add in the onions, and sprinkle with the canning salt. Stir well to combine and coat the cucumbers and onions with salt.

Cover the bowl with a damp towel or plastic wrap and allow it to rest at room temperature for 2 hours.

With about 45 minutes left before the time is up, you can start preparing your jars, lids, and canner for canning. This includes washing all of your equipment (jars, rings, jar lifters, funnels, etc) and your canner if needed.

Add the canning lids to a small saucepan filled with water and bring to a low simmer. Keep the lids warm until they are needed for processing the jars.

Once the time is up for the cucumbers and the onions, transfer the mixture to a colander placed over the sink to drain off any excess liquid. Rinse with cool running water, aiming to rinse off much of the salt from the vegetables.

Once the cucumbers and onions are thoroughly rinsed and drained, set them aside.

Add the vinegar, sugar, mustard seeds, celery seeds, and turmeric to a large stainless or nonreactive saucepan. It should have a volume of at least 16 cups (4 quarts) to give you adequate space for your brine and cucumbers.

Whisk the brine ingredients together and bring to a boil over medium-high heat, stirring often to dissolve the sugar.

Once the brine has come to a boil, stir in the drained cucumbers and onions and return to a boil.

Remove the jars from the hot water of the canner, and empty them of any water. Pack the vegetables into the hot jars, leaving a generous ½ headspace at the top of the jar. Then, ladle in the liquid brine to cover the vegetables. Use a butter knife or de-bubbler to remove any air bubbles and add liquid if needed to maintain a ½” headspace at the top of the jar.

Wipe the rims with a clean towel or paper towel, and place a lid on each jar. Then, secure each jar with a canning ring and secure until fingertip tight (tighten with your fingertips, stopping when you get resistance).

Place each jar back into the canner, ensuring that they are covered by 2 inches of water. If the water level is not high enough, add enough hot water to cover the jars (I like to keep a kettle handy). Add the lid to the canner and bring it to a boil.

Once the canner has returned to a rapid boil, the processing time begins. Keep the lid in place and allow the jars to process for 10 minutes.

Once the processing time is up, turn the heat off and remove the canner from the heat source. Remove the lid and allow the canners to rest in the canner for 5 minutes.

Once the 5 minutes are up, remove the jars and place them in a location where they can go undisturbed for at least 24 hours.

As the jars seal, you should hear a “pop” from each jar. Allow up to 24 hours for each jar to seal, but in my experience, if they are going to seal, it’s going to be within the first few hours.

After 24 hours, check the seals and remove the canning rings. Wipe down the jars and label them. Any jars that have not been sealed should be moved to the fridge to be eaten right away.

I recommend waiting for 1-3 weeks before opening and enjoying your pickles, as they are so much better when the flavors have had the opportunity to mingle.