Citrus plants are the most popular plants of the group with ornamental fruits and today there are dozens of citrus clubs and associations throughout the world which perform further cross-breeding, try growing the plants outdoors in the open and publish a number of specialized journals. In truth, these are very attractive plants that have decorative foliage, prettyand furthermore, a lovely fragrance. The fruits are brightly coloured, fragrant, persistent and, what is more, also edible.
Citrus plants (the genera Fortunella, Citrus and Poncirus) are an extremely difficult group to classify for they have been grown and crossed for thousands of years. Opinions as to the classification of the individual species differ and thus, for example, the number assigned to the genus Citrus ranges from 16 to 60 according to different authorities. The genus Fortunella has not been fully worked-out yet, either, and at the moment comprises from 6 to 10 species.
All citrus plants are native to south-east Asia and most (including the species) require cool conditions in winter (about 10°C [50°F].) Indoors they will thrive only if they are put in a room where the heat can be turned off or else in an unheated conservatory.
Fortunella japonica (syn. Citrus japonica), despite its name, is a native of China and was introduced to Japan, where it was described, as a decorative plant. It is a small shrub with fragrant, pink flowers and numerous small fruits (only about 3 cm [1-¾ in] across). It is a favourite house plant which tolerates even very cold conditions in winter, particularly if it is grafted on Poncirus trifoliata.
Recommended for home decoration are the mandarin ‘Unshiu’ and the lemon ‘Meyeri’, both of which tolerate conditions in a centrally-heated home and reliably bear a profusion of flowers and fruits. Theshould be a heavy, nourishing mixture such as John Innes potting compost No. 2 or 3, depending on the size of the pot.