Winter seems like an odd time for fruit to ripen. Winter weather is cool enough to inhibit vascular activity in plants. That is why most plants are dormant to some extent through winter. Most familiar fruit trees are deciduous, so defoliate in winter chill. Stone fruits ripened through early summer. Pome fruits ripened through late summer and autumn. Nonetheless, citrus fruits are now in season.
The various citrus fruits and their cultivars ripen at various times through their season. Like stone fruits and pome fruits, they are on distinct schedules. Furthermore, climate affects ripening. Citrus fruits that ripen earlier than other cultivars in a particular climate may ripen after the same other cultivars in another climate. A few cultivars produce sporadically, or notably later than citrus season.
Such cultivars are justifiably popular. For example, ‘Eureka’ lemon is a mutant of ‘Lisbon’ lemon. ‘Lisbon’ lemon works well for orchards because all the fruit ripens within a limited season. ‘Eureka’ is more practical for home gardens because it instead produces sporadically throughout the year. A few fresh lemons are always available. The winter crop is abundant, but not too overwhelming.
Mandarin oranges are the first citrus fruits to harvest, even if they are not the first to completely ripen. Because their rinds fit so loosely, they are the most perishable of citrus fruits. They will oxidize and dehydrate before they rot. Tangerines are the same, since they are merely American descendants of Mandarin oranges. ‘Rangpur’ lime is not a lime at all, but a sour Mandarin orange hybrid.
Oranges, lemons and grapefruits, although ripening now, can remain on their trees for quite a while. The tartness of grapefruits mellows with age, and might be preferable after a few months. The same applies to the acidity of lemons. However, too many lingering citrus fruits can inhibit bloom. Some limes are supposedly best before totally ripe. All citrus fruits stop ripening when harvested. Juice of the various citrus fruits can be frozen for storage if necessary.