Hostas are a vast genus of shade-loving perennial flowering plants in the lily family. They grow and naturalize from underground rhizomes, as varietals rarely come true from seed. Hostas can live up to 40 years or longer. They can become crowded or bare in their centers over time and will respond well to division once every 3-5 years. The preferred time of year to dig and divide hostas is in the late summer or early fall after flowering has finished for the season.
Excavate widely around the circumference of the hosta root ball, at least as far out from the crown of the plant as the drip line. Mature hosta plants can have very large root balls and it is virtually impossible to excavate a large plant without severing some roots. The goal should be to keep the thickest mass of the root ball intact when excavating it.
Lever the root ball up and out of the soil with your shovel or spade and place on stable soil. Use your spade blade or a clean garden knife to excise small portions of the plant in 3- to 8-inch chunks that each have several growth eyes or leaves and a good hunk of roots.
Keep the divisions moist at all times while they are waiting to be transplanted. Mist with tepid water after dividing and if need be store wrapped in moist burlap or moist peat moss if they must be out of the ground for more than an hour or two.
Transplant the divisions into nutrient-rich, moist soil at the same planting depth at which they were previously growing. Allow at least a foot of space between the divisions to accommodate regrowth to a mature size.