When life gives you lemons, it is likely this time of year. Although, the most popular garden varieties of lemon, like ‘Meyer’ and ‘Eureka’, continue to produce at least a few more fruits sporadically through the year. ‘Lisbon’ lemon that is still used in orchard production, and is the ancestor of the household ‘Eureka’ lemon, produces almost all of its fruit in winter, and blooms shortly afterward.
Ripe citrus in the middle of winter impresses those in climates where winter is too cold for much to happen in the garden. They could not grow a citrus tree if they wanted to. Even here, frost can damage some of the more sensitive citrus varieties, like ‘Mexican’ lime. Unlike the fruits of summer, citrus fruits ripen slowly and are not so perishable, so do not need to be harvested right away.
This means that if it is raining, cold or just to wintery to go outside, citrus fruits can be left on the tree until the weather improves. Most of us prefer to pick them in small batches anyway. Ideally, fruit should get picked as it is consumed. Lemons and limes typically get picked individually as needed, until there are so many that some need to be bagged and shared with friends and neighbors.
Mandarin oranges are the most perishable of the citrus. Because their skins are so loosely attached to the pulp, the pulp can oxidize, lose flavor and eventually get dry and pithy. Incidentally, a ‘tangerine’ is merely a Mandarin orange that was developed in North or South America. A surprisingly sour (unknown) Mandarin orange might really be a ‘Rangpur lime’, which is not a lime at all.
Unlike most fruit that continues to ripen after harvest, or pears that actually delay ripening until after harvest, citrus fruits stop developing flavor once picked. It is best to taste them for confirmation of ripe flavor prior to harvest. Some Mandarin oranges may have slightly greenish blotches on them even when completely ripe. The best ‘Valencia’ oranges can look rather yellowish. Grapefruits might mellow if left in their trees past ripeness, but can also inhibit bloom.