I was unsure about this, but I had so much zucchini last season that I figured 'what did I have to lose'. So:
We shredded the zukes.
Mixed and Cooked the Ingredients
Filled the jars
Bathed the jars (this is after bathing which is why the water is no longer boiling)
And added the labels.
Finally about 2 or so months later, we ran out of our store-bought relish. I looked dubiously at these jars. Said what the heck. Popped one open. Applied a small amount to my turkey dog. Took a bite. There has been no turning back since. All of my turkey dogs are now eaten with zucchini relish. This stuff is delicious! A great way to use your extra zukes; especially the overgrown seedy ones...they are perfect for this since they are shredded.
I keep forgetting to look at the jars to see where I got the recipe (I include that on the label). But I think I got it from the Ball Canning Book. Ball has this recipe online, but I know I didn't have any horseradish; so I doubt this is the one I used. This recipe looks more like the one I used. I am sure that either would be just as delicious.
Give it a try; you've got a hundred and two zucchini anyway.