Hostas in Spring:
Do not water your hostas until the threat of frost subsides. If watering is done early, the foliage may come up prematurely, and suffer from a late frost.
(Late spring frosts seem to affect plantaginea and lancifolia the most.) By keeping the leaves in the ground as long as possible, it’s also easier to clean up leaves and sticks without worrying about stepping on hosta pips coming up. When the pips are still in the ground, it’s safe to apply 10-10-10 fertilizer without burning the hosta leaves.
Hostas in Summer:
As a part of routine seasonal hosta care, it is important to keep the roots of your hostas moist. This especially applies to plants in direct sunlight and in the hottest months of July and August. Hostas should receive about one inch of moisture per week.
Fertilizing hostas can be done throughout the season, but do not fertilize after July 31st. You can usually divide hostas in the summer if you keep new divisions well-watered.
Hostas in Fall:
In Minnesota, we have divided plants in October and replanted successfully. Many gardeners advise not transplanting after 6 weeks before the first frost. Since you do not know the amount of winter snowcover and moisture your hostas will receive the following winter, it is a good idea to water your gardens thoroughly in the fall. If your gardens dry during the winter due to lack of snow cover, severe wind, or an exposed slope, you may have stunted hostas the following year. We cut our hostas right to the ground with bread knives (disinfecting our knives in 10 to 20% bleach solution after every cutting) each fall and remove the dead leaves to reduce the risk of spreading diseases and the proliferation of slugs. Slugs produce many eggs in the fall, so it is also a good time to apply slug killer.
Hostas in Winter:
Most hostas are winter hardy to U.S.D.A. Growing Zone 3. (See Growing Zones.) Hostas that are newly planted may benefit from a fall covering of leaves or straw, The additional soil protection will allow roots to grow even longer in the winter. Removing dead hosta leaves and surrounding the root sytems with plant matter in the fall will help reduce the multiplication of slugs and plant diseases. Unfortunately, your garden will not benefit from the normal decay of plant matter.