Growing Kumquats- The Pop-in-Your-Mouth Fruit
By Laurelynn Martin and Byron Martin
The Kumquat is thought to have originated in Southern Japan and China. It was originally known as the “gam kwat” with an early reference in the 12th century. Kumquats are loved for their oval, oblong or round tiny fruit that produce abundantly on small trees in the ground or in containers. The bite-size, pop-in-your-mouth fruit have edible skin. Some varieties are sweet on the outside and tart on the inside; others are sweet all the way through. In 1864, Robert Fortune, a collector from the London Horticultural Society introduced kumquats to Europe, and shortly thereafter to North America. In 1915, Kumquats were no longer classified as Citrus japonica but were named after Mr. Fortune and the new genus became Fortunella.
At Logee’s, we grow four varieties of kumquats. We grow them as grafted plants rather than cuttings because they don’t root readily and grafting the named variety onto an understock increases vigor and encourages early fruiting. We typically use Citrumelo or C. macrophylla as the rootstock.
‘Nagami’ (Fortunella margarita) This kumquat is often found in produce sections of your grocery store. The fruit is small and oblong and is typically more sour than the other varieties.
‘Nordmann Seedless Nagami’ (Fortunella margarita) The teardrop shaped fruit is tart and juicy and completely seedless. The fruit ripens from December to June.
‘Meiwa’ (Fortunella crassifolia) is the sweetest kumquat that we grow and it is sweet and delicious inside and out. It has a small round shape.
‘Changshou’ (Fortunella obovata ‘Fukushu’) is slightly larger than the other kumquats and also has sweet skin with a sweet inner flesh. The Changshou bears fruit heavily and can produce fruit twice a year.
Fortunella hindsii is another ornamental kumquat that makes an excellent bonsai. The fruit, although edible, is small and pea sized and has mostly seed and skin. Logee’s doesn’t grow this variety.
Full to partial sun is required for growing kumquats. The more light the better but as with all citrus, they can be grown indoors on an east or west-facing window and flower and produce fruit.
The flowering cycle for kumquats is later than most citrus. They flower in late spring into early summer with the Changshou often flowering twice a year, making it an almost ever-bearing plant. The sweetly fragrant blossoms are followed by fruit that ripens in mid-winter for us with the fruit holding onto the trees well into late spring. They bear a heavy crop at a young age making them excellent specimens for a container fruit garden.
Kumquats are well adapted to most well-drained potting mixes. We grow them in a standard soilless mix that has a pH around 6. For outdoor growing, kumquat plants are cold hardy to Zone 8b and upper 9 and are known to be some of the more cold tolerant citrus. The Changshou is thought to be more cold sensitive than the other species.
Moderate amounts of fertilizer are needed during the active growing season. Reduce and restrict fertilizer when going into the winter season. There are several excellent citrus fertilizers on the market but any organic balanced fertilizer will work. We like to top dress the soil, because it slowly releases fertilizer to the plant over a period of time.
When the kumquat plant is young, pinch back the growing tips and shoots to make the plant full and bushy. This encourages a sturdy well-branched structure so it can carry the future fruiting load. Keep in mind that kumquats bear so heavy that they can bend the limbs to the point of breaking on young plants. Older plants need to be pruned periodically to maintain shape and this is best done after fruiting. On mature plants, it’s best to selectively prune top branches that are too tall or reaching out but leave the inner and side growth so you don’t lose next year’s fruit. A branch or lead that is cut in late spring or early summer generally won’t flower until the following year.
Scale, spider mite and mealy bug can be problems on citrus. Attention needs to be given when moving plants indoors in late summer or early fall. A preventative spraying of neem oil twice in one-week intervals will do wonders to keep the kumquat tree clean throughout the winter. This is especially true if scale and mealybug have been a problem in the past. Spider mites often come in with plants that have summered outside and are not visible until the dry atmosphere of the winter home causes populations to explode. Root disease is only a problem if the plant is kept too wet and grown in cold damp conditions. We recommend growing in a clay pot and erring on the dry side when watering. Also, if you have a grafted plant that has been grown on a disease resistant understock, then root disease becomes less of a problem.
Special Requirements for grafted plants
Remember when grafted kumquat plants are young, shoots can develop below the graft union on the rootstock. These shoots need to be removed, otherwise they will dominate the plant and the grafted kumquat variety will stay small and barely grow. As plants get older, this rootstock suckering slows down or stops.
- Growing Tasty Tropical Plants in any home, anywhere. By Laurelynn Martin and Byron Martin, (Storey Publishing, 2010)