I forgot that Wasabi was a radish; I always thought it was some sort of powerful Horseradish, but they’re probably related somehow.
I had Horseradish coming up through BLACKTOP at my other farm. It’s hard to kill!
https://www.youtube.com/watch?time_continue=3&v=fhlklE9wBSY&embeds_referring_euri=https%3A%2F%2Fboingboing.net%2F&source_ve_path=Mjg2NjY&feature=emb_logo
Clean running water, but I am not sure if freezing kills them, otherwise you could grow them in Wisconsin! ($100/Lb
https://territorialseed.com/products/wasabi-wasabi currently out of stock.