It is a common misconception that hostas are wet loving plants that want to be in boggy soil all of the time, quite the opposite in fact. Hostas, like a lot of other herbaceous perennials, thrive best in moist, free draining soil. Persistent, saturated soil can result in rotting roots and very sad plants. On the flip side, soil that is bone dry (under a tree for example) is also less than ideal. Very dry soil will result in stunted plants that struggle to get to their full potential. Watering in a High Nitrogen Feed during the growing season is also wise.
Hostas Planted in the Ground
When you first plant hostas in the ground, it is wise to supplement the watering during their first year and sometimes their second as they put out new roots. If your hostas are planted in good soil that is moist and free draining, you will rarely have to water these after the first year. If the soil is challenging and dries out regularly, then additional watering will be required. You may consider putting in irrigation such as a soaker hose or sprinkler to help you keep onto of it. If the area you have planted in is naturally wet and lacks drainage, do not supplement watering, even in the first year. You may consider adding additional drainage to help avoid you plants rotting.
Once your plants are mature and established they will be a lot more tolerant of extreme conditions, whether it is very dry or very wet.
Hostas in Pots
When watering hostas in pots, it is never one size fits all. Freshly potted plants may need very little water, as the soil that is not yet occupied by roots is able to retain moisture much better than a pot that is well rooted. It is important not to overwater miniatures or freshly potted plants, always check the soil with you fingers to see whether it is damp or dry.
Your choice of pot can also affect will also change the demands of watering. Terracotta pots absorb water from the soil which can result in the plant drying out faster. Ceramic pots are able to hold water better but this can lead to overwater especially if you have a mix of the two.