The old Germans where I grew up said that horseradish needed to be dug in a month with an 'r' in it, September through April. -- usualluy in the late fall. We never dig all the plants at once, but divide in late August early September like peonies. With a ten year old plant -- you could likely take about half of the roots, and leave the rest for next year, and transplant. Nels in ND > My Dad asked me to ask about a horseradish that my mother planted. He would like to know when the best time to dig it up would be and can we dig up part or does it need to be all? Can we replant what we don't need?