The best time to cut back hostas is after they have died back in fall, though the specific timing depends on geographic location. For coastal areas, the ideal time is October or early November; for areas further inland, the ideal time is September or the beginning of October. The proper height to cut the stalks down to is approximately 2 inches tall, just enough to keep the stalks above the ground.
When cutting back hostas, it is important to remove all leaves from the plants. Leaving the dead leaves on the plant does not damage it in any way, but slugs, weevils and rodents enjoy the withered foliage.
Dead foliage might also contain viruses and other pathogens; removing the dead hosta leaves prevents the spread of disease.
Hosta virus X is the most common disease to affect hostas, but it shows up differently in each type of hosta. Most of the time, the indicator of disease is blue or green spots on light-colored leaves. Leaf tissue might also appear lumpy and appears may have a different texture than the rest of the leaf. More severely affected leaves may even be deformed and have brown spots on them. Diseased darker hostas have a bleached appearance, but they also may display the other indicators.
Besides removing these infected leaves, it is also important to disinfect any tools used to cut back the plants.