Citrus x paradisi
Family: Rutaceae

Although the grapefruit possibly originated from Southeast Asia, the fruit we know today probably developed from a hybrid from the West Indies. It has long been an important commercial product and over time has been improved through breeding and selection so that it is now not so acidic. Citrus x paradisi is an evergreen tree which grows to around 5 m (16 ft). The large, round fruit have a white or pink, pulpy flesh and can weigh to 2 kilograms (4½ pounds). Recommended cultivars include 'Marsh', 'Ruby', 'Wheeney', and 'Star RubyGrapefruit are a valuable source of vitamin C and are usually consumed fresh or as a juice.

Cultivation

Grapefruit tolerates cold less than the orange but it can be grown outside in the warmer parts of zone 9. In lower zones it must be grown in an intermediate greenhouse or conservatory. Grow in large pots of soil-based potting compost. Ensure good light but shade from direct sun. Plants can be stood outdoors for the summer if desired. Outdoors, grapefruit will grow in any good soil, but needs good drainage. No citrus, in fact, can stand 'wet feet'. Plentiful water is required to fill out the fruit and keep the foliage in good condition. Grapefruit likes full sun but needs shelter from cold, winter winds. Propagate by budding of proven scions onto rootstocks resistant to soil-borne diseases.

Container-grown trees can be planted out at almost any time but it is proba­bly best to avoid midwinter. Plant established container-grown stock as they are ahead in growing time, should be well shaped, and not usually affected by transplanting. Little or no pruning is necessary, except to remove dead wood and broken branches, and to encourage a canopy of leaves to shade the fruit.

Citrus are heavy feeders so a complete plant food should be applied in winter and late spring. It is not advisable to feed from late summer to autumn as the new flush of growth will be most susceptible to attack by citrus leaf miner. Use organic mulches, too, but well clear of the trunk. Always spread fertilizer within the leaf drip zone, as it is here that the root hairs will absorb nutrients. For the home garden, allow a 2-3 m (6-10 ft) diameter area around each tree; on undulating land, space the trees along the con-tour to prevent soil erosion.

Allow grapefruit to mature on the tree and gather with care so as not to bruise. Use secateurs to cut the stem, retaining part of the stem on the fruit. Insect pests may need to be controlled by sprays; fungi are the main problem in moister climates. Collar rot can be minimized by not injuring the scion and by planting trees so that the graft is well clear of the finished soil level.

Climate

Zone 9 (warmer parts) and zone 10.