I have not planted horseradish from seed but I would. I purchased this plant as a baby organic plant from a local Cidery. The radish is planted in a heavy deer browse area, they actually bed down just on the other side of the hugel mound. I have currants that are two years old and they look like seedlings. :)
If you plant from seed it will just take a little longer to get established. Maybe? For me, most perennials don't gain footing until the second spring. I planted asparagus from seed last spring and it is very delicate.
"An ounce of action is worth a ton of theory."
Ralph Waldo Emerson