Extension Educator, Horticulture
Gardeners are plagued with zonal envy. Whatever grows in warmer zones, we want it. For centuries citrus trees have been high on the wish list. Victorian England coveted citrus. Buildings and gardens were designed specifically to house citrus trees. An orangery was a glassed-in structure typically with a short stone wall. The surrounding formal gardens were the summer home to the prized citrus. Today's counterparts to orangeries are greenhouses or sunrooms.
It's not hard to see why these globes of perfection would be objects of affection. In addition to the healthy fruit, citrus trees have lovely thick glossy green leaves and the sweet thick fragrance of their waxy white flowers hijack you to a tropical island.
Some types of citrus can make nice houseplants. Seeds from your orange snack will grow, but because of their large mature size and thorns they don't make good houseplants. Plus it takes many years for these to flower. Ones that bloom and fruit reliably indoors include Meyer lemon, Ponderosa lemon, Otaheite orange, Persian lime, calamondin orange and kumquats.
Dwarf Meyer Lemon is one of the easiest to grow. It flowers twice a year in spring and fall, so flowers and fruit often grow simultaneously. The fruits are light yellow and can reach 3 inches in diameter. Young plants bloom readily with a refreshing lemony fragrance.
Calamondin oranges also bloom when they are very young at only one foot tall. The bright orange fruits are small at 1-1.5 inches and very sour to eat right off the plant. Fruit are best made into marmalade. Calamondins also produce many flowers and fruit at the same time. The ripe fruit will stay on the plant for several months. Calamondins are slow growers, thornless and make nice 3-4 foot tall plants. Calamondins are one of the more reliable citrus to produce flowers and fruit indoors.
Flowers are normally insect pollinated. When they flower indoors they may need some help for fruit to form. Flick the flowers with your fingers or use an artist's brush or cotton swab to move pollen from flower to flower. Sometimes small fruits will fall off the plant if they were poorly pollinated or environmental conditions are not right. Depending on the species, fruit may require several weeks to months to ripen.
Citrus plants can adapt to low light and cool temperatures indoors, but they may never flower. For best flowering they need a greenhouse or an area with supplemental light. Lights should be close to the plant within 8-10 inches. One of our master gardeners puts his citrus in the garage during the winter. Gardeners are good at maintaining the American tradition of housing everything but a car in the garage. His citrus live under shop lights containing fluorescent grow lights. Even though the temperature in his garage can get to 45-50 degrees F, they grow nicely. Citrus can survive cool temperatures but some need heat for the fruit to ripen.
Use a well-drained soil mix in pots with good drainage. Keep soil moist but not soggy. Don't let them dry too much when they are producing flowers or fruit or they may drop off. Use a humidifier or place pots on pebble trays to help raise the humidity. During the summer use a fertilizer for flowering plants every couple weeks.
Citrus are best kept outdoors in the summer. Move plants to a shady spot once all danger of frost has passed in May then bring back indoors before temperatures get below 50 degrees F.
Watch for insects, especially spider mites and mealy bugs. Insecticidal soap will help to control insect pests.
Give a citrus plant to a gardening friend and be sure to attach two tickets to Florida.