Citroncirus

• Citrumelo

The following notes are based on Citrus species. They are probably applicable here as well, even though this is a bi-generic hybrid, since any seed might be produced polyembrionically.

The seed is best sown in a greenhouse as soon as it ripe after thoroughly rinsing it^[1][2]. Sow stored seed in March in a greenhouse^[3]. Germination usually takes place within 2 - 3 weeks at 13°c. Seedlings are liable to damp off so they must be watered with care and kept well ventilated. The seed is usually polyembrionic, two or more seedlings arise from each seed and they are genetically identical to the parent but they do not usually carry any virus that might be present in the parent plant^[2]. When large enough to handle, prick the seedlings out into individual pots and grow them on in the greenhouse for at least three growing seasons before trying them outdoors. Plant them out in the summer and give them some protection from the cold for their first few winters outdoors. Cuttings of half-ripe wood, July/August in a frame.

Layering in October.

Prefers a moderately heavy loam with a generous amount of compost and sand added and a very sunny position^[4][2]. When growing plants in pots, a compost comprising equal quantities of loam and leafmould plus a little charcoal should produce good results^[5]. Do not use manure since Citrus species dislike it^[5]. When watering pot plants it is important to neither overwater or underwater since the plant will soon complain by turning yellow and dying. Water only when the compost is almost dry, but do not allow it to become completely dry^[5].

Reasonably cold resistant, dormant plants can tolerate temperatures down to about -10°c, especially if they are grafted onto a Poncirus trifoliata rootstock^[2]. The young growth in spring, even on mature plants, is frost-tender and so it is best to grow the plants in a position sheltered from the early morning sun[K].

A group of hybrids of garden origin, Poncirus trifoliata x Citrus paradisi^[6]. Generally, these hybrids combine the qualities of cold hardiness and bitterness from Poncirus trifoliata with the larger fruits of the grapefruit, Citrus paradisi^[6]. They are occasionally cultivated for their edible fruit, but more usually for their use as a rootstock, there are some named varieties^[6][2].