As a general rule of thumb - Wisteria 'Amethyst Falls' can be once a year, and this can be a light prune. As 'Amethyst Falls' is naturally compact and not as vigorous, there is no need to prune as much as you might typically do with traditional Wisteria forms. Instead, only take a few inches of growth off from the whole body of the plant. Also, remove any branches/stems heading in directions you do not wish for the plant to grow. As Amethyst Falls is grafted, it's important to remove any basal shoots coming from the base of the plant, as this growth can very quickly overthrow the plant if left uncared for. The best time to prune Wisteria 'Amethyst Falls' is early summer after flowering has finished. However, this timing may differ a little depending on your climate and territory. In addition to pruning, having your Wisteria 'Amethyst Falls' growing in a nice sunny position in humus-rich soil that drains well will certainly help with its flowering. As for feeding, apply a feed once a year; you can use a palette form such as 'Grow Better; Organic Fertiliser' or even Troforte 'All Purpose' - both very good fertilisers.