Horseradish is one of those wonderful plants, that despite our best efforts, refuse to die, and is forgiving of almost anything.
If the ground doesn't freeze where you are at, horseradish can be harvested at virtually anytime of the year, though its flavor is strongest and most aromatic when its dormant or in my zone
, 9, in the fall and winter.
To replant, save the biggest and fattest portion of a root cut into 2" long sections. I've found the fungal powder optional, if you wish, you can let your cut parts rest for a few days to dry out a little before you replant. As long as your garden doesn't stay overly wet, you should be fine.