That's an easy one. It is horseradish. Roots can be harvested in fall after frost to make ground horseradish and various condiments/sauces from it, if so inclined.

Garden heresy to say this, I know, but I have a couple of big plants and haven't harvested them for years and years. I use very little horseradish, just once in a while, and its just easier for me to buy it ready to go. It is VERY pungent and can be sort of torture to prepare it -- like cutting pungent onions on steroids.

One warning on the horseradish - it is the most aggressively spreading plant that I have in my garden. If you dig it up and leave just a smidgen of root - the smidgen will reproduce. The worst thing to do is to run a tiller over it and shred the roots all over your garden - instant horseradish field... But I do love the stuff - to peel and grind, we do it outside with safety goggles on. Really.

Enjoy!
Cindy

Horseradish leaves are great to add to cucumbers during fermentation (dilled cucumbers). Horserarish leaves makes ferments more crispy and add flavor.
olga