As this immature grapefruit ripens it will change from green to bright yellow and become increasingly juicy and delicious.
Grapefruit, the tree, resulted from a cross (no doubt unintentional) between a sweet orange (Citrus sinensis) and a pummelo (C. maxima). (This knowledge comes not from the historical record, but from genetic analyses conducted many years later.) The grapefruit tree gets 20-50 ft (6-15 m) tall, is evergreen, and bears white, very fragrant four-petaled flowers in early spring. Grapefruit, the fruit, is intermediate in size between the pummelo and the orange, but unlike either parent, is acidic instead of sweet. (Go figure.) Grapefruit fruits and the flowers that precede them tend to be in clusters, like grapes; hence the name. Grapefruit cultivars include white fleshed varieties: 'Duncan' is probably the hardiest grapefruit; it is rather seedy, but probably the best tasting grapefruit, and usually eaten fresh. 'Marsh' is seedless, has a hollow center and is often used for juice. Pink or red fleshed cultivars include 'Ruby' which is similar to 'Marsh' but with red flesh; and 'Flame' which is also red and fairly cold hardy. The grapefruit has been backcrossed to the pummelo to create 'Oro Blanca', a cold hardy citrus with some of the best characteristics of both parents. Intentional crosses between the grapefruit and the mandarin (C. reticulata), have yielded the tangelos, 'Mineola' and 'Orlando', both of which are grown commercially in Florida.
The grapefruit (Citrus X paradisi) was brought to Florida in the early 1800's from Barbados in the West Indies, where it is believed to have originated. Its parents, the pummelo and the sweet orange are believed to have originated in Polynesia and China, respectively. The United States is the major producer of grapefruit, with most commercial production in Florida and California, and some production in southern Texas and Arizona.
Culture Light: Citrus trees do best in full sun but can tolerate partial shade although they will not be as productive. Moisture: Soil for growing citrus should be well drained. Irrigation is necessary when a drought lasts more than two or three months. Hardiness: USDA Zones 9-11. Well established grapefruit trees can tolerate temperatures that dip briefly into the low to mid 20's F (-6 to -3° C). 'Duncan' grapefruits are being grown successfully in USDA zone 8B. Propagation: Most grapefruits are bud grafted onto rootstocks chosen for specific characteristics such as cold hardiness, resistance to drought, resistance to soil borne disease, etc. Seeds will come true however, and you can start your own grapefruit tree by planting a fresh seed in a pot and maintaining for a year or two before potting on or setting outside. It is not uncommon for numerous volunteer seedlings to appear beneath 'Duncan' grapefruit trees, and these can be dug up and transplanted. Expect to wait 4-5 years before fruit production begins with seedling trees. Grafted trees may bear within two years.
Grapefuit makes a fine dooryard tree that can provide a family-size supply of fruit throughout the season.
Like other door yard citrus plantings, grapefruit trees require very little attention. They usually need no supplemental watering; fertilize once a year in spring; enjoy the fruit in winter. The lovely "orange blossom" fragrance attracts bees and the nectar is made into a honey of superior quality. Grapefruits last longer on the tree than most citrus fruits, and sometimes the seeds begin to germinate within the fruits still on the tree.
Grapefruit is high in vitamin C, soluble fiber, and (especially the red varieties) lycopene. Grapefruit consumption has been shown to lower blood cholesterol levels. Proponents of the "grapefruit diet" hold that the fruit's low glycemic index causes an increase in metabolism of body fat. Oils extracted from grapefruit peelings are used in aromatherapy.
Compounds in grapefruit have the unsettling characteristic of increasing the efficacy of certain medicinal drugs that are taken orally. This was only recently discovered when several deaths were attributed to drug overdoses brought about by consuming grapefruit or grapefruit juice along with the normal dosage of the drug. It turns out that certain compounds in grapefruit inhibit an enzyme in the human intestine which then leads to an increase in the effectiveness of certain drugs. (It's as though the dosage of the drug had been increased.) Drugs taken intravenously are not affected. A prudent patient would check with his physician about possible interactions between prescribed medications and consumption of grapefruit.