Starting a home orchard can be fun and rewarding, but space might become an issue when choosing the best trees. The kumquat tree (Fortunella spp.) is a naturally compact tree that's also available to gardeners in a dwarf variety. It produces small, round-to-oblong fruits with a sweet-sour flavor and grows in U.S. Department of Agriculture plant hardiness zones 8 or 9 through 10, depending on the variety.
The kumquat tree comes from China and other parts of Asia, where its name means "golden orange." Although several species exist, all are slow-growing trees that have a naturally shrubby, compact form and usually grow no taller than 15 feet. Among the widely cultivated varieties, "Nagami" (Fortunella margarita "Nagami") becomes about 8 feet tall and 6 feet wide when fully mature, flowers in summer and has mature fruit in late winter. Another variety called "Meiwa" (Fortunella crassifolia) is a dwarf tree that becomes about 4 feet tall when container-grown and a bit taller in the ground. It produces especially sweet kumquats and grows outdoors year-round in zones 9 through 10, while "Nagami" is more cold-tolerant and grows in zones 8 through 10 .
The kumquat tree is generally slow growing, adding 1 foot or less to its height each year. It prefers a spot in full sun, but can tolerate partial sun for a few hours each day. In regions with hot, strong summer sun and relatively warm winters, locate the tree where it gets full morning sun, followed by light shade in the hotter afternoon hours. The tree doesn't do well in full shade, where it could fail to bloom and produce fruit. In colder portions of the tree's range, planting it in a sunny, warm spot, such as near a south- or west-facing building wall can help protect it from winter cold. Locating it on a hillside can also help it come through winter unharmed, because cold air drains to lower parts of the slope.
Soil and Water
The kumquat tree grows in any type of well-drained garden soil and doesn't thrive in especially wet, soggy areas. Adding some coarse sand to your planting site can improve your soil's drainage if it contains clay and tends to drain slowly. The tree needs even moisture to establish a strong root system, especially when it's young. If you grow a dwarf specimen in a pot, avoid allowing the soil to dry out for long periods and re-pot the tree into a larger container if it becomes pot-bound. It's especially important to provide moisture for the tree while it's blooming or fruit is developing, because dry spells can cause flowers or fruit to drop.
Adding a 3- to 4-inch thick layer of organic mulch at the tree's root zone in spring helps conserve soil moisture, while keeping down weeds that compete for soil nutrients. Although a kumquat can tolerate some frost in winter, an especially cold spell during spring can injure its young growth. You can protect the tree during these periods by covering it with a blanket during cold nights and mornings, adding extra warmth if needed by placing a lighted electric bulb inside the tented blanket. A container-grown tree can be moved indoors during winter and early spring, where it does well in a brightly lit, south- or west-facing window.