Combine the chopped vegetables in a large nonreactive kettle or bowl. Add the salt and stir to combine thoroughly. Cover and let stand for 4 hours or refrigerate overnight.
Prepare the canner and jars. Add water to a canner with rack and heat to a boil; reduce heat and keep at a simmer. The water should be high enough to be at least 1 inch above the filled jars. I usually fill it about halfway and I keep a kettle or saucepan of water boiling on another burner to add to the canner as needed. Wash jars thoroughly and heat water in a small saucepan; put the lids in the saucepan and bring almost to the boil; lower heat to very low to keep the lids hot.
Drain the vegetables and rinse thoroughly.
In a large nonreactive kettle, bring the vinegar, brown sugar, and seeds and spices to a boil. Reduce heat to medium low and continue simmering for 5 minutes. Add the drained vegetables and bring back to a boil. Reduce heat to medium low and simmer for 10 minutes.
With a slotted spoon, pack the vegetables into prepared jars. Cover vegetables with the pickling liquid, leaving about 1/4-inch headspace.
With a clean dampened cloth, wipe the rims of the jars. Place the flat lids on the jars then close caps with screw-on rings tightly, but do not over-tighten. Arrange the filled jars in the canner and add more water, as needed, to be at least 1 inch above the jars. Bring to a full boil. Cover and continue boiling for 10 minutes. Remove the relish to a rack to cool completely.
Check for seals (the middle of the caps should have made a popping sound while cooling and will stay depressed.