The Arts and Craft movement was a design movement initiated by the writer and artist William Morris which was at its height between 1880 and 1910. It is likely that the adjective 'arty-and-crafty' derives from the movement. In becoming adjectival, however, it has taken on a slightly derogatory meaning, implying a design style that represents a bastardized version of the original Arts and Crafts tenets.
It is Elfine's tendency to 'arti-crafti-ness' which bothers Flora Poste, and Stella Gibbons manages to paint a very vivid picture of Flora's understanding of the concept by describing some of the tendencies, styles of dress and so on of those who have gone down the 'arty-crafty' path. Among these she includes 'keeping a tea-room in Brighton' or an 'arts and craft shop in Horsham'; doing barbola work; wearing smocks 'embroidered with hollyhocks' or 'orange linen jumpers'; possessing 'hand-wrought jewellery' such as 'a pendant made of hammered silver with a bit of blue enamel in the middle'; and last but not least, trying to grow herbs!