Can I substitute fresh horseradish for jarred?

Going off of what jwolfsthal said...

When I substitute fresh for jarred, I soak it in vinegar for about 30 minutes, drain and then add a dash of vinegar to the recipe I'm using it in

Check out the Best Recipe with Horseradish under contests.

you can but fresh horseradish is VERY sharp, so you will want to use less. Jarred Horseradish is usually pickled in vinegar, so also has a bit more tartness and sweetness, so you may want to add some vinegar to balance.