One of the hardiest citrus fruit trees, kumquats (Fortunella swingle) primarily grow in Florida and California in hardiness zones 9 to 10 where the warm climate helps the plant produce delicious little fruits. The shrubby trees work well in borders or as single specimens with their clusters of small orange fruits. Kumquats also grow well in large containers although they require protection from frost and cold weather.
Kumquats grow as shrubby, compact evergreen trees, with a few reaching heights up to 15 feet in maturity. The tree sports thornless branches with glossy green leaves reaching up to more than 3 inches in length. The tree produces fragrant white flowers followed by small oblong green fruits that reach 1.5 inches in length. The fruits slowly turn into bright orange, yellow or scarlet mature fruits ready for harvesting, usually in late winter to early spring. The small fruits offer a tart, tasty treat. The peel and the fruit are both edible.
Since kumquats rarely grow from seeds and instead get grafted onto other citrus stock, most gardeners use transplants in the landscape. Choose a sunny location, then dig a hole that's two to three times larger than the size of the rootball. Kumquats prefer sandy loamy soil, so add organic matter to the soil to help it drain well. Plant the kumquat at the same depth as the container it came in. For areas outside the growing zone, consider planting a kumquat in a large container with good drainage holes. Bring the container inside during cold weather or when the threat of frost occurs.
Maintenance and Fertilization
Newly transplanted kumquats require regular watering during their first year to help establish a deep root system. Before new growth appears in the spring, feed kumquats with a general purpose fertilizer. Like most citrus trees, kumquats thrive on nitrogen, making an application of foliar spray such as fish emulsion a good idea. The tree requires no pruning since it tends to grow in a beautiful mound shape all on its own.
One of the most important aspects of growing kumquats focuses on protecting it from frost or cold weather. Once winter starts, add a 6-inch mound of soil around the trunk of the tree, then cover that with a few inches of mulch. Remove the dirt and mulch as soon as the threat of frost disappears. Some gardeners string Christmas lights all over the tree with the warmth of the lights protecting the tree during minor frosts. Adding blankets or dropcloths to the tree during heavy frosts or cold nights may also help prevent damage.
Kumquats grown in containers remain susceptible to mealybug infestations. While kumquats grown in the landscape remain resistant to citrus canker, they may experience attacks from the more common citrus pests including mites, scale and leafminer. Careful use of insecticides, such as chlorpyrifos, helps eliminate some of these pests.