Place chopped cucumbers and 1/4 cup salt in a colander over a bowl and toss to combine. Cover, refrigerate and allow to drain overnight. You will have a large amount of water in the bowl the next morning.
Drain and rinse cucumbers in ice cold water, filling the bowl. Drain well; this helps to remove the excess salt.
Chop peppers and onions. Add to cucumbers.
In a separate bowl, combine sugar, horseradish, celery seed, and mustard seed. Let sit at room temperature until sugar dissolves. Add to cucumber mixture and then add enough vinegar to cover.
Bottle in your favorite jars and store in the refrigerator for up to 6 weeks, freeze, or give as gifts to friends.