If you’ve never seen citrus anywhere but the produce department, the idea of plucking a lemon or lime from your own tree can either spark a pang of jealousy or inspire you to try your hand at growing citrus indoors.
Citrus trees thrive outdoors year-round in USDA Hardiness Zones 10 and 11. In Zones 9 and lower, chilly temperatures ring the death knell on outdoor citrus plants. However, if grown in pots and brought indoors when the thermometer dips, gardeners anywhere can grow these fascinating plants.
Sweet and Sour Choices
Often, you’ll be limited in your tree choice by what your nursery or garden catalog has to offer, but one choice you’ll need to make is between sour and sweet citrus. Unless you keep your home blazing warm over the winter, steer clear of sweet citrus such as oranges, mandarins, and tangerines that need plenty of heat to ripen fully. Instead, opt for sour citrus like lemons, limes, kumquats, or calamondin whose fruits ripen in normal household conditions.
Containers and Soil
Since citrus trees thrive when their roots stay lightly moist, the best container material is terra cotta. The porous surface keeps air flowing and water evaporating from the soil making for healthy citrus roots. Plastic or other non-porous containers promote soggy soil that leads to root rot and other fungal diseases.
Your citrus tree’s size will be limited by the size of its container. Although dwarf trees can reach heights of 10 feet, a tree in a 16-inch pot will remain a manageable size of approximately 3 feet tall.
As far as soil goes, you can pay the price for a specialty citrus blend, but a basic potting mix with a pH between 5 and 7 works just as well. Because citrus trees suffer in wet soil, avoid mixes that contain materials for moisture retention or wetting agents.
Light and Heat
If you only want to grow citrus for their shiny, evergreen foliage, leaving the trees in front of a bright window in a room that never dips below 50 degrees will keep your plants healthy and full of leaves.
If you do want fruits and flowers, you’ll need to mimic the long, sunny days of citrus-growing climates with a grow light. No, not the energy-consuming monsters used for marijuana operations. A simple, 24-watt, full-spectrum light left on for 10 to 12 hours a day works ideally for citrus and promotes flowering and fruit development. If you’re worried about your energy bill, don’t. A 24-watt bulb uses less electricity than your laptop.
Although citrus can be kept indoors year-round, they will benefit from spending time outside whenever the temperature rises above 50 degrees. Outdoors, place your trees in the sunniest spot possible. Citrus trees love heat and sun. One warning: First-year trees have thin bark that can burn in intense sun. Protect young trunks by shading this portion of the tree or by wrapping it in cloth. Once both daytime and nighttime temperatures refuse to climb above 50, it’s time for the trees to come inside until the weather warms again.
Feeding and Watering
Over-watering and the fungal diseases that result from it are the primary destroyers of container-grown citrus trees. Wait to water your citrus until the top three inches of soil feel very dry and then give the soil a thorough soaking. An hour after you’ve watered, drain any excess water from the pot’s drainage tray.
Citrus trees love to eat. You can skimp on the soil for your trees, but don’t skimp on a quality, organic food specifically intended for citrus. Feed your trees according to the package directions in late winter, late spring, and late summer.
Pruning and Pests
Container-grown trees are typically grown on the dwarf root stock of Poncirus trifoliate. “Trifoliata” means “three-leaved.” If you notice spurs growing from the lower portion of your tree and the spurs open to show off a leaf with three leaflets, cut the spurs off at the trunk. These spurs are the rootstock trying to grow and will sap energy away from your tree.
To shape up your tree, control its size, and keep it healthy you’ll occasionally want to prune your tree. Trim away any branches that are rubbing, no longer producing leaves, or showing signs of disease, but never remove more than one-third of the branches.
When roots become crowded, citrus growth grinds to a halt. If your tree appears healthy, but seems to have stopped growing, you can remedy this stagnation by transplanting to a larger pot, or by thinning out any old, thick roots and keeping the plant in the same pot.
As with foliage, do not prune out more than one-third of the roots.
Most healthy, indoor trees will remain pest-free, but if aphids and mites make an appearance the easiest way to deal with these pests is to take your trees outside and give them a quick blast of water with the hose to knock the bugs off.
Blooming and Fruiting
Although citrus can be grown for their foliage alone, the true joys of citrus are their fragrant, white flowers and tasty fruit. Bloom time depends on the variety of tree you choose, but most trees flower sometime between late summer and mid-winter.
Most citrus trees available are self-fertile and don’t need a pollinator or another tree to fertilize the flowers. However, you can increase fruit production by hand pollinating the flowers of your trees with a small paintbrush.
Dwarf citrus trees should produce fruit within their first year. The best way to determine ripeness is to know what the fruit of your tree’s variety looks like when it’s ripe. In general, ripe fruit has a bright color and a slight give when pressed. Of course, you can always taste test for ripeness.
Your indoor citrus grove may not rival the expanses of fruit trees in southern climates, but it’s hard to beat the excitement of plucking a lemon from a houseplant you’ve tended.