LN Gardening: Citrus Fruits

Is there anything better on a dull January day than a succulent, fresh-from-the-sunny-South Honeybell orange or a zippy, aromatic Meyer lemon? Persian limes, Ruby Red grapefruit, Valencias and Mandarins all have the capacity of conjuring up exotic tropical locales. They are the brightest spot in my winter kitchen.

Growing a Golden Treasure

    Growing citrus trees has been a popular hobby for hundreds of years. Many of our modern favorites are descendents of Chinese wild plants. They migrated over the ancient trade routes and arrived in Europe during the Renaissance. Tropical in nature, the tender trees could not survive in colder climates without protection. Early winter shelters were made from translucent waxed canvas. By the mid-16th century, Italians were making simple lean-tos of many small glass panes along south-facing walls to protect potted fruit trees. As glass manufacturing became more sophisticated in the 17th century, the Dutch and French built magnificent orangeries with larger south-facing windows. Heating systems were added and the orangeries moved northward to England. Our Linnean House at the Missouri Botanical Garden is patterned after one of these historic buildings at Chatsworth, seat of the Duke of Devonshire.

A Basket of Limes

    Oranges, Meyer lemons, Key limes, calamondins, kumquats, tangerines and Kaffir leaf lime can be grown successfully as potted houseplants. They love to spend summers outdoors on the terrace and then move into a sunny kitchen window for the winter. Blooming in January and February, there is nothing more heavenly than the fragrance of lemon blossoms in the winter sunshine. If you grow your own citrus and it blooms indoors, you must play honeybee and pollinate the flowers with a small brush or Q-tip. Otherwise, there will be no fruit.

How Do You Choose?

    Our perception of the flavor of citrus juice depends most strongly on two factors: the sugar/acid ratio and the type and amount of aromatic oil in the skin. Two other characteristics that help define varieties are seediness and ease of peeling. Fruits must have 10 seeds or fewer to be called ‘seedless’ in the marketplace.

    Some citrus fruits have such plentiful and appealing oils in the skin that we extract them to use as flavoring agents and in perfumes. Bergamot orange is the most famous, with the extracted oil used to give the distinctive flavor to Earl Grey tea. Bergamot is also one of the best perfume bases and is found in about half of all women’s perfume!

The Wild Citrus Ancestry

    The taxonomy of Citrus is confusing, at best. From a botanical perspective, the new treatment in the Flora of China, by David Maberly and Dianxiang Zhang, published by the Missouri Botanical Garden, successfully straightens it all out. There are now about two dozen species total in the genus. Some of them are known only from cultivation, and the early loss of any one of these wild types would have seriously reduced the diversity of today’s fruit. Imagine if C. hystrix had been lost before hybridizing with others—there would be no limes, no Key lime pie and no margaritas! From crosses between these few species, there are hundreds of named hybrids. In order to try and sort out the complicated citrus relations, let me begin with a few of the most important wild species:

    Leaf lime (C. hystrix) or Kaffir lime, is a wild species from southeast Asia, where its foliage is used to season food. If you have ever had Vietnamese chicken-coconut soup, you will have run into it. Kaffir lime is the source of galangal (a type of ginger), hot peppers, lemon grass and green lime leaves. The fruit of this species is not edible, grown just for the wonderful perfume.

    Wild kumquat (formerly Fortunella reticulata, now Citrus japonica) still occurs on the hills of Hong Kong, with many cultivars in the marketplace. They range from round to oval, with the fruits about the size of a smallish pecan. Candied, pickled or made into marmalade, kumquats are called ‘gold orange’ in China. ‘Nagami,’ the oval kumquat, is most frequently seen in U.S. produce markets, often used as a table decoration, and cooked or processed before eating.

    Citron (C. medica) is a thick-skinned fruit with few or no juice sacs inside. Think of it as a very large, warty, dry lemon. Candied citron peel is essential to most fruit cakes and German stöllen. Called etrog in Hebrew, the citron is used as part of the Jewish festival of Sukkot, where it is regarded as a symbol of the heart, and represents a person who has knowledge of the Torah and does good deeds.

    The pomelo (often seen as pummelo, C. maxima) is the citrus species with the largest fruit, reaching a size close to that of a middling watermelon. Lost from the wild, it is known only in cultivation. It looks like slightly green, very large grapefruit. This resemblance is more than skin deep, as the pomelo and citron actually are the parents that interbred to produce the grapefruit. It marries well with cilantro, fish sauce and chilies, or when juiced, makes a sprightly beverage on its own.

    The Mandarin orange (C. reticulata) is native to southeast China. Like pomelo, Mandarins are now found only in the cultivated forms. This group has many variants, including the tangerine, all with thin, easily peeled skins. The three groups of hybrids within this parentage are Mandarins, with very fragrant orange-yellow skin and many seeds; Satsumas, the Japanese swarm of seedless cultivars; and tangerines, a group of Mandarins with red-orange skin.

    Clementine, a seedless tangerine hybrid of uncertain parentage, is my all-time favorite fruit. Refrigerate them as they spoil quickly. And if you get a seedy one, blame it on the bees, since they can carry the pollen of other oranges, resulting in seeds.

    Stay tuned for the next chapter in February, when I will help sort out the wonderful varieties of lemons, and limes and the tangled tree of oranges, grapefruits and tangelos!