Kumquat Trees-The Most Cold Hardy Citrus

Kumquat trees are grown commercially in Florida, Louisiana, Texas, and California. The Florida climate appears to be most favorable for profitable commercial fruit production because of its predictable balanced temperatures. Most old timers remember Christmas when the kumquat fruit appeared on grocery store shelves with a few twigs and leaves attached to the fruit displayed next to shelved orange, grapefruit, lemon, and other Christmas stocking delights. The kumquat fruit appears to have an extended shelf life, if the twigs are attached to the fruit. In years past, the clusters of kumquats were sold by weighing clusters, however, now they are sold prepackaged in ½ pint plastic containers. The market for fresh kumquats never seems to be quite satisfied and customers will return year after year to empty the shelves just a few days before Christmas.


Cold Hardy citrus can usually be achieved by grafting a kumquat cultivar into a trifoliate (wild sour orange tree) rootstock. This grafted kumquat tree is a dwarf which has a growth quality transferred into the growing scion, that slows the growth and hardens the bark, thus, empowering the tree with a resistance to cold damage. The Marumi Kumquat appears to be the most cold hardy citrus plant, and the Marumi Kumquat is not damaged by temperatures of 10 degrees F, however, even at colder temperatures, the Kumquat tree will lose its leaves at 0 degrees F, but the leaves will usually regrow within 30 days. The observation of winter dormancy in the Kumquat is quite remarkable and not characteristic of other citrus plants.


After the Kumquat fruit is harvested in January, the winter growth is suspended for several months, exhibiting no flowers or bud elongation. The Kumquat plant might completely or partially defoliate, before extensive flowering, and shoot growth restarts in the Spring and Summer. Kumquats growth form is usually that of a bush posture rather than a tree form (unless the lower limbs are removed to elevate the fruiting process) far enough from the ground to prevent mud or soil splashing onto the fruit. In cool or cold weather, the kumquats can remain fresh on the trees from October through January.


The Kumquat Bush is easily hybridized between species and even wide crosses with orange, grapefruit, and lemon-lime are known to exist. The remarkable variety of growth form, color, and flavor of citrus is believed to have evolved from very ancient plant ancestors that were used by gardeners mainly to add fragrance, and the evolution and new development of the fantastic variety of hybrid fruit. New citrus tree varieties have transformed the food supply of the world and have made the earth a better place to live. The climate and planting sites have a profound effect on the size of kumquats, the color and the flavor. Hot summers with temperatures rising to 95-100 degrees F will enhance the size, flavor, and color of kumquats.


The kumquat can be successfully and easily grown in pots and containers in northern cold climates, not only in greenhouses, but any citrus plants can be grown indoors when planted next to a window or a well illuminated warm spot. Some citrus growers prefer to grow a kumquat bush indoors and when the weather warms, the plants can then be moved outside. When grown in pots, kumquat trees can be further dwarfed, since the root system will be confined, and the root temperatures will be cooler if grown in porous pots rather than in the earth.


Kumquats are used in many different ways, but fresh eating from the bush is a most popular entertainment for kids at Christmas. Many preservatives are used in preparing for food in the future. A jar of kumquats filled with salt will dehydrate the kumquats into a tasty brown citrus treat that can be kept for years in the liquid salt solution. Kumquat fruit can also be preserved by boiling briefly in water and placing them into jars filled with sugar-water, honey or preserving them in alcohol solutions such as gin, rum or brandy.


Marumi Kumquat, Citrus japonica, "Marumi"


The Marumi Kumquat, Citrus japonica, “Marumi”, is considered to be the most cold hardy citrus tree; even more cold hardy then other kumquats like the Nagami and the Meiwa- and even more cold hardy than the Satsuma Orange Tree. The Marumi kumquat is round at 1 ½ inches, somewhat smaller than the Meiwa, but with seeds smaller. The leaves of the Marumi kumquat are smaller than other kumquat cultivars, and the white flowers and orange-yellow fruit are fragrant and the peel is thin, sweet, and the overall flavor is balanced-sweet and sour- and spicy to the taste. The Marumi kumquat was imported into Florida in 1885 from Japan and widely distributed at that time throughout the South from the Royal Palm Nursery.


Some citrus plants such as the sour orange tree can be grown from the seed and the sour orange root system offers dwarf qualities, cold resistance, and resistance of the roots to nematodes, fungi, and bacteria. Kumquats cannot be reproduced commercially by nurseries from the seed, because of the root problems. This seed grown root problem of kumquats can be solved by grafting the stock onto sour orange stock.


The Meiwa kumquat, Citrus crassifolia, “Meiwa” was imported into the United States from Japan in 1910, often called the “sweet kumquat”, the Meiwa kumquat has a thick, sweet flavored orange-like peel with a rather bland-sourness core; sometimes seedless, and sometimes many seeds are embedded in the pulp. The Meiwa kumquat is round and two inches long, producing numerous clusters of kumquats that ripen from October through January, and can be eaten even in a green-orange color stage as a pleasantly flavored kumquat; unlike the Nagami kumquat that cannot be satisfactorily eaten, unless it is completely orange in color. The branches of the Meiwa kumquat are densely twigged, and the white summer flowers are richly fragrant. The Meiwa kumquat flowers grow into a round fragrant green fruit that ripens into a yellow-orange color. The Meiwa kumquat is cold hardy to 10 degrees F without any damage, and is considered to be even more cold hardy than the Satsuma Orange. The Meiwa kumquat is suspected to be a hybrid blend cultivar-a cross of Citrus japonica “Nagami” and Citrus japonica “Marumi”.


The Nagami kumquat, Citrus japonica “Nagami” was introduced into England in 1846 by plant collector and explorer, Robert Fortune in 1846 and exported to Florida nurseries in 1850. The Nagami kumquat grows into a two inch, orange, elongated shaped fruit with a thick peel, sweetly flavored, and with a sour inside, but when eaten together a delicate balance of sweet-sour blend of powerful citrus aromas, and the taste satisfies the most critical palates of food gourmets. The Nagami kumquat begins ripening in October and continues through January. The fruit can sometimes be seedless, and usually is eaten only after it has turned completely orange for maxium sweetness development. The Nagami kumquat is the most widely commercially grown kumquat for fresh market citrus and is the most popular backyard kumquat planted in areas where the kumquat will survive cold temperatures of 10 degrees F.