Orange Trees are relatively easy to grow indoors. If you choose a standard non-dwarf variety , or grow one from seed - it could be years before you see any fruit. Specific dwarf varieties, such as Mandarin [not a true orange] ,calamondin and trovita , do well when grown inside as long as you maintain the basic temperature, soil, and light conditions.
They keys to successfully grow oranges indoors are basically the same as with all citrus ,good light, adequate temperature and humidity , well-drained potting soil, proper nutrients, and consistent moisture. Without any single one of those failure looms.
Orange trees are generally container-grown, and purchased online or from a local nursery. They can also be propagated at home from cuttings, and seed.
If you decide to grow orange Trees from seeds, allow the seeds to dry out for up to two weeks. Once dried, plant the seeds about an inch deep in good potting soil and cover with plastic wrap. Once the seed has germinated it should be placed in a sunny location.
Any container used for orange trees and any indoor fruit trees, should provide ample drainage and room for growth. Any citrus started from seed will have a very long maturation period and a non dwarf tree will need to obtain substantial height before fruiting..
Orange trees can be put outdoors during the summer months, this is recommended to increase their chances of bearing abundantly. When grown indoors they do not have the advantage of pollinators, bees and other insects. Placing them outdoors during the summer allows for this. You can also hand pollinate them See : Indoor Pollination
Prune as necessary to shape the tree. Pruning will also encourage new branch development, and create a more compact and appealing shape. orange trees that don't get enough light can become spindly and unhealthy. Should this occur, prune about 1/3 off the top growth and place the tree in a sunnier location or under grow lights.
Oranges require 8-12 hours of sunlight daily to prosper, 5-6 hours to just survive . Grown indoors, a South or west facing window is best . Not that I'm comparing apples to oranges, but citrus plants unlike other fruits do not normally go through a period of dormancy or hibernation in the winter, but will tolerate slightly lower light conditions during this phase of slower growth.
Supplemental light , such as grow-lights or fluorescent plant lights will help them produce better, especially if your location is not optimally sunned.
Night time temperatures no lower than 55 degrees F and daytime temperatures around 70 - 80 F are ideal. They will usually tolerate temperatures hovering above 32 degrees for a few hours or heat over 100 degrees so long as they are well watered. Temperatures should however , not be a major problem in an indoor environment. Temperatures below 55 will will invoke a dormancy , extended periods below 55 could result in their premature demise.
You should be using a light [low clay], well draining soil mixture with an abundance of peat, and perlite or vermiculite. Adding addition perlite or vermiculite to any soil you purchase is advisable. You can also add wood chips, redwood shavings or even hamster bedding and semi-sterile compost [Not from your back yard compost heap] in moderation . Using dirt from your yard is a bad idea.
During the winter months Fertilize the orange tree with 20-20-20 fertilizer at half strength or citrus specific fertilizer at half strength once monthly. During the summer, fertilize with full-strength fertilizer once monthly. Orange trees will benefit from a mildly nitrogen rich or balanced NPK fertilizer. Micro-nutrients such as copper, zinc ,magnesium, manganese, iron, and boron. They prefer an acidic soil, so an acidic fertilizer can also be beneficial in citrus tree fertilizing, though not absolutely essential.Fertilizer developed specifically for citrus trees is naturally best.
You can also feed an orange trees weekly during its active growing season with a liquid citrus fertilizer. If you prefer to feed frequently , used at least half strength - over fertilizing and feeding can be more harmful than none at all.
Water regularly to keep the soil moist, not saturated, just moist. A layer of decorative sterile mulch such as bark or any other organic mulch is advisable to retain soil moisture. Allow the potting soil to slightly dry between watering, not "DRY-OUT" just slightly dry.
I prefer to water modestly 2 - 3 times weekly , test the soil by hand - stick your finger in about a half inch to be certain it is semi dry before adding more water. Over watering is just as deadly as under watering.
In winter months, artificial heat dries the air so plants will need added humidity.
Most indoor environments have relatively very little humidity as opposed to their natural environment. Any building that has heat or air conditioning will usually have no more than 15% humidity at most. Citrus plants need much higher levels just to survive and 50% or better to thrive and produce.
Symptoms of Humidity deprivation are
1. Plants begin to wilt.
2. Leaves develop brown edges.
3. Flower buds do not develop .
4. Flower buds drop from the plant before opening.
5. Flowers shrivel soon after opening.
Significantly increasing humidity indoors is good for the plants , but it's not good for you or your home unless of course you like mold, mildew, bacteria, mites and so forth.
There are however a number of ways you can increase humidity for the plants without seriously damaging your personal environment.
1. You can add moisture with a humidifier.
2. Cluster your plants in tight groups. All Plants naturally exhale moisture through their leaves in a process known as transpiration, Citrus trees are no exception. By grouping citrus as well as other indoor plants together, you add to a more suitable environment in the immediate growing area.
3. Misting the trees foliage with a simple spray bottle is good way to help citrus cope with the indoor environment.
4. You can add moisture with a humidity tray, a pebble filled tray with water added to the top of the pebbles. As the water gradually evaporates, it raises the humidity in its immediate vicinity enough to improve conditions for the tree.
Orange trees are susceptible to spider mites, mealy bugs and scale. Check the trunk for mealy bugs and scales. Wipe the foliage periodically with a damp paper towel or sponge. Dust will attracts pests, they hide themselves and their egg clusters in the dust while parasitizing the plant . To treat spider mites, spray your plant with insecticidal soap or horticulturist oil, which will smother the insects. clean the foliage, top and bottom sides of the leaves as well. Neem Oil is effective against Scales and Mealy bugs. Rubbing alcohol applied with a Q-tip will also work in mild infestations.