If you wish to grow horseradish as a perennial, you can leave horseradish in the ground over winter if sown in late fall or in winter – and harvest the following fall. However, if sown in the spring, it is best to harvest horseradish just after the first frost. Horseradish takes around eight-10 months to fully grow, so don’t leave in the ground over winter if you sowed the previous spring, as this will result in tough and bitter roots.