Mandarin oranges are not actually the same species as Oranges. They are citrus, of which tangerines are one variety.
The Mandarin orange is a small yellowish orange sweet fruit. One key difference between mandarins and oranges is how easily the skin separates from a mandarin as opposed to an Orange.
Mandarin oranges prefer warm, humid climates, temperatures over 70 degrees F and full sun . The trees are somewhat cold hardy, but the fruit is easily damaged in any temperatures approaching freezing.
The keys to successfully grow Mandarin 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.
Mandarin orange trees are generally container-grown, and purchased online or from a local nursery. Dwarf mandarin trees grow to 5 to 6 feet tall at maturity, depending on the container size and nutrition.
Mandarins grown in containers are generally not as big as those grown in the ground and their fruit capacity diminishes as well for that reason.
Trees provided with sufficient light and good care will produce fruit in direct proportion to their size. In most cultivars you shouldn’t expect flowering and fruiting for the five years of planting, some cultivars are quicker. Check with your supplier.
Many varieties of Mandarin can be grown indoors.
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 Mandarin 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.
Mandarins are much more cold hardy than other citrus trees , they have survived temperatures Hovering near zero degrees Fahrenheit, the fruit will not survive – but the tree will. Most mature cultivars will remain hardy down to at least 25°F.
Mandarin 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.
You should always acclimate them (hardening) before putting outdoors for extended periods , as well as before returning them to the indoor environment for extended periods.
Prune as necessary to shape the tree. Pruning will also encourage new branch development, and create a more compact and appealing shape.
Mandarin 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.
Light
Mandarin 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 Mandarin 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.
Temperature
Night time temperatures no lower than 55\ degrees Farenheit 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.
Soil
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.
Fertilizer
I prefer to fertilize my Mandarin oranges and Tangerines by a slightly differing schedule from other citrus in my collection. Fertilize annually starting in the early spring when new growth has begun to appear and repeat this process and in Mid spring and again in late summer .
One-year-old Mandarin orange trees should be fertilized with an additional cup of either ammonium sulfate or citrus tree fertilizer divided equally over the three feeding sessions. Increase the application to 2 cups for 2-year-old trees and continue this regimen for the third year.
By the 4th year cut back to 1 cup twice annually – starting with the early spring and ending in late summer. It’s okay to add some other fertilizer from time to time but don’t get carried away.
Excessive fertilizer can do more harm than good. Fertilizer developed specifically for citrus trees is naturally a good choice.
Water
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.
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:
- Plants begin to wilt.
- Leaves develop brown edges.
- Flower buds do not develop .
- Flower buds drop from the plant before opening.
- 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 a 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.
If you are delving into indoor gardening ~ indoor plants you might want to consider a hygrometer, an indoor temperature and humidity monitor.