This large tropical and subtropical group covers a wide range of juicy fruits that require almost frost-free climates to produce fruit (most can take 25°F to 28°F for several hours) and hot summers to help ripen and sweeten the fruit. These trees need temperatures between 70°F and 90°F for best growth. In the United States, the citrus-growing region is limited to Florida, coastal areas of the Gulf coast states, and parts of Arizona and California.

Citrus trees have evergreen foliage, and most have thorny limbs. Trees are usually grafted. Most species bloom in early spring and don’t require cross-pollination. Fruit ripens from autumn to spring, but some everbearing trees produce fruit year round. Allow fruit to ripen on the tree for best flavor. Here’s a look at some of the popular citrus fruits:

• Grapefruits: Grown primarily in Florida and southern Texas, the trees reach 30 feet in height. Varieties include both seeded and seedless types and those with red, pink, or white flesh.
• Kumquat: A bit hardier and smaller than most citrus trees, kumquat can tolerate temperatures as low as 18°F to 20°F and also make good houseplants. You can eat the small fruit whole — rind and all.
• Lemons and limes: Among the most cold-sensitive citrus, this group grows best in frost-free climates. Some varieties do well as houseplants, producing the sour fruit indoors.
• Mandarins: Members of this large group have somewhat flattened shapes and loose, easy-to-peel skins. Varieties include tangerines, clementines, and tangelos. The ‘Calamondin’ variety makes a good houseplant or container shrub and produces loads of small fruit with edible rinds. Most mandarin varieties need Zone 9 and warmer, although ‘Calamondin’ and ‘Satsuma’ varieties tolerate temperatures down to 20°F.
• Oranges: You can choose from many varieties, which vary in ease of peeling, sweetness, number of seeds, hardiness, quality of the juice, color, and time of ripening. Although most types ripen during December and January, some are ready to pick in November, while others, such as juicy Valencia varieties, don’t ripen until late winter to spring. Navel oranges are among the hardiest varieties.

Annual pruning isn’t necessary for citrus trees — a good thing, given that most of these trees sport long, sharp thorns. They require pruning just to keep the centers of the trees open to light and air and to remove dead branches. If trees get too big to pick easily, you can cut back the limbs with thinning cuts every year or two. Wait to prune frost-nipped trees until new growth shows the extent of damage. To prevent sunburn after pruning, paint exposed branches that were previously shaded by foliage with whitewash made from a 1:1 mix of water and a white, water-based paint.

Citrus demands moist but well-drained soil and regular applications of nitrogen fertilizer beginning in January and ending in late summer. Make sure that trees have adequate water when they’re actively growing and developing fruit. Pests and diseases infrequently cause problems, except when trees are stressed from drought or other weather-related factors. Scale, mites, thrips, and whiteflies may infest these trees, and so can cankers that infect the wood.