Dig in! Hosta can be divided up any time of year if the ground is not frozen. I've done the dirty deed in August on a hot day and in December in the rain. Hosta is one tough perennial and seems to survive divisions by breaking off a small hunk with a shovel or by dividing it into large chunks with an axe. Don't worry about the foliage. As long as you plant a piece of the root with an eye or growth bud, it will sprout new leaves in the spring. Check out the videos on this website for step-by-step lessons on plant dividing and planting: How to Divide and Replant a Hosta Plant and How to Divide Hostas. Good luck!