Combine first 5 ingredients in a large glass mixing bowl; add salt, mixing well. Add water to cover. Cover and let stand in a cool place overnight. Rinse and drain well. Set aside.
Combine sugar, vinegar, and mustard and celery seeds in a stainless steel stockpot; bring to a boil, stirring until sugar dissolves. Add vegetable mixture. Reduce heat; simmer, uncovered, 30 minutes or until vegetables are tender, stirring frequently.
Quickly ladle relish into hot sterilized jars, leaving 1/2-inch head space. Remove air bubbles. Cover with metal lids, and screw bands tight. Process in boiling water bath 10 minutes. Serve with meats or vegetables.