The long and short of it A few years ago we split h. 'Amy Elizabeth' as part of our collection plant maintenance. Left with a final small piece we popped this into a bonsai pot fearing it would get lost in one of the regular size pots. Needless to say, we didn't get around to re-potting the plant into a regular sized pot but this doesn't seem to have affected the plant's growth. Indeed it has flourished but at a fraction of the size of what the characteristics of h. 'Amy Elizabeth' would dictate. As the photograph shows, the restricted h. 'Amy Elizabeth' is around half its expected growth size. The size of the leaves and the height of the flower spikes are in direct proportion, even the flowers look as though they may be half their expected size when they unfurl. The resulting plant looks like a bonsai version of the original!

Hostas that become too crowded in their pots tend to produce smaller leaves, particularly in the centre of the plant mound. Eventually the over-crowded parts of the plant mound will die back. This is why hostas benefit from splitting when they become too densely packed as this helps ensure the plant retains its characteristics. This fundamental fact about hosta growth is why we haven't previously considered restricting our plants - perhaps we now can?

Hostas in a bonsai landscape
Bonsai growers are always in need of plants they can use within their landscape arrangements. Obviously suitable plants need to be in scale with the landscape under construction.
There have been many 'miniature' hosta cultivars introduced over recent years that could be used to compliment some of the larger-scale bonsai landscapes. However, many of these cultivars still appear rather large in this context.
So, could some of these miniature cultivars be grown even smaller in the same way as h. 'Amy Elizabeth'? We think they could, but perhaps only temporarily as containment will eventually have an adverse effect on the habit of a hosta. Some parts of the plant mound would probably begin to die back if overcrowded for too long. A key characteristic of hostas is their generally speedy growth rate. As a consequence it should be possible to contain successive pieces of a plant in order to supply a series of complimentary plants for use in bonsai landscapes.

Photo courtesy of Mendip Bonsai

We have listed some miniature varieties in the side column, which could be especially suitable for this treatment. Each variety is already among the smallest of the miniature category and containment could reduce their size even further. In particular, varieties such as h. 'Yakushima Mizu' and h. 'Paradise Puppet' could produce a good supply of tiny plants for bonsai displays as they are vigorous growers, producing small but perfectly formed carpets of leaves in a short space of time.

Varieties such as h. 'Radio Waves' (on the right) might prove more temperamental to grow in a contained way but it is already one of the smallest cultivars, so a likely candidate for further miniaturisation.
A smaller version of h. 'Radio Waves', with it's exotic habit, would be an ideal addition to a bonsai arrangement.
So we suggest you give it a go and try to create some 'contained' miniature hostas for yourself.
Just remember that they may not last very long restricted in this way and perhaps should be allowed to return to their natural size if they begin to look stressed.