Growing Citrus Indoors

Published: January 1, 2008

Want to try your hand at something different? With a little effort, you can grow your own orangerie, just as Louis XIV’s gardeners did so he could enjoy the fragrance of orange blossoms in his own conservatory. Not only was Louis XIV captivated by the scent of orange blossoms, but the fruit as well. The popularity of citrus continued to spread as it was introduced on all continents. Today, the sweet orange (Citrus sinensis) is the most commonly grown tree fruit in the world. Though most people are familiar with the sweet orange cultivars, such as ‘Valencia,’ ‘Hamlin, and ‘Navel’ orange, the sour orange and many of its citrus relatives that can grown indoors are relatively unknown.

Thus, in Missouri, sweet citrus trees tend to be difficult to grow and overwinter indoors, but can be moved outdoors during the warm summer months. In contrast, acid citrus species are easy to grow in containers inside and many will bear several crops of fruit per year if given optimum growing conditions. Citrus trees grown indoors require a nursery container at least 14 inches in diameter with a loose, well-drained potting mix maintained at a 5.5 to 6.5 pH. A half whiskey barrel also makes a good container, as long as it has drainage holes drilled in the bottom. Because citrus favor a sunny climate, the trees should be placed in a room kept at 55 to 68 degrees Fahrenheit with a southern exposure with at least 8 hours of bright light per day. Trees also require high humidity (30-60 percent). Because most homes have an average humidity of only 15 to 20 percent, a cool mist vaporizer or humidifier may be used to raise the humidity. Alternatively, placing the container on a pebble tray that is partially filled with water and misting of the foliage frequently helps raise the humidity. A soluble citrus fertilizer that is formulated to maintain the medium at a slightly acidic pH may be applied about once a month, or a slow-release fertilizer can be pre-mixed into the potting medium. Trees require water when the top 2 or 3 inches of the potting medium feels dry. Over-watering is a common cause of fruit drop.

Most citrus trees grown indoors are grafted onto a dwarfing rootstock such as trifoliate orange (Poncirus trifoliata), Brazilian Sour, or Flying Dragon (Hiryu). While many citrus plants can be grown from seed, they tend to be large trees and may take more than 7 years to bear fruit. Because citrus trees are self-fertile, multiple trees are not required for pollination. However, if kept inside year-round, shaking the tree gently when flowers are open will facilitate pollination. Alternatively, pollen can be transferred from one flower to another using a cotton swab or small paintbrush.

There are many different types of citrus trees that can be grown indoors. For example, Calomondin sour orange is frequently grown as an ornamental with its fragrant while flowers and bright orange fruit (resemble small tangerines) even though its fruit is edible. ‘Blanco’ mandarin “orange” (Citrus reticulata) is not a true sweet orange because the peel easily separates from the very sweet fruit segments. ‘Meyer’ lemon trees are small, with few thorns, very fruitful and long-lived. ‘Meyer’ lemons have a slightly sweeter flavor than the commercial cultivars sold at grocery stores. ‘Ponderosa’ lemon trees produce a few fruit at a time, but they are juicy and very large, often as big as a sweet orange. ‘Ponderosa’ lemons also have a thick rind that extends their storage life.

Key (or Mexican) lime trees produce abundant, faintly fragrant flowers and that develop relatively small fruit. These limes are prized for their distinctive aroma and uniquely acidic juice. Originally used in the famous Key Lime Pie of the Florida Keys southern Florida, it is often replaced by the juice of the Tahiti lime today. The Tahiti or Persian lime produces slightly purple-tinged flowers throughout the year, but most are produced in January. Tahiti limes are vivid green, but lack the bouquet of the Key lime. Kaffir “lime” (Citris hystrix) is a misnomer for true limes. Trees produce thorns and the fruit has a bumpy rind. The leaves are used as a spice in cooking Southeast Asian dishes.

Kumquat trees produce abundant fruit that are generally eaten whole, including the rind. Meiwa kumquats are rarely found at the grocery store but are small, round, pale orange fruit with a sweet flavor unlike that of the more common Nagami kumquat that is tart. The other “quats” are interesting hybrids of other citrus species and kumquats. They are prolific fruit producers that are most often used for ornamental purposes. The limequat is a cross between a Key lime and a kumquat that was originally made in 1909. These trees produce bright yellow fruit about the size of an egg. The orangequat is a cross between the Meiwa kumquat and the Satsuma mandarin. The citrangequat is a cross of kumquat and citrange (orange x trifoliate orange). The acidic fruit is like an oval kumquat and has been used to make marmalades.

If you enjoy a beautiful plant, like an enticing floral scent, love to eat fruit, or enjoy using an unusual spice, there is a citrus tree for you that can be grown indoors with ease!