Growing Mandarin Oranges Indoors

Start mandarin orange seedlings in spring to take advantage of their natural growing seasons, as well as convenient summer sun and temperatures. Use healthy nursery seedlings for best results and quickest fruiting.

Prepare 10-gallon clay pots with drainage holes for starting the seedlings. Smaller pots offer easier movement and plenty of starting space, though the trees sill require eventual transplant. Line the bottom of each pot with 1 inch of gravel to catch water; mandarin orange trees fail with muddy soil or standing water around their roots.

Give mandarin oranges a rich, crumbly and quick-draining soil with 2 parts soil-based organic compost to 1 part vermiculite or 1 part peat moss to 1 part sand and 1 part vermiculite. Potted trees require better moisture and nutrition in their soil than in-ground trees as soil access is limited, and mandarin oranges require high nutrition to bloom and produce their fruit. Fill each pot half full of potting soil, and mix slow-release 10-10-10 fertilizer into the soil for more nutrition.

Plant smaller mandarin orange tree cultivars like Wase, Owari, Ponkan and Clementine for full harvests with compact growth. Give each seedling a pot of its own. Spread the roots across the soil and cover them with more soil, filling the pots until the seedlings' bud onions sit at soil level. Plant multiple seedlings to ensure pollination and fruit harvest with these trees, which are sometimes self-infertile.

Put each mandarin orange seedling in an indoor or outdoor site with full sunshine and air movement, and temperatures of 60 to 80 degrees F. Don't put the trees near fireplaces, which will dry and air and tree. Never expose the trees to temperatures under 30 degrees F.

Water each tree with 1/2 gallon of water to establish the planting, and start the trees on 2 inches of water every week. Monitor the soil for drying and increase watering frequency as necessary to keep the trees from drying out.

Feed the mandarin orange trees with slow-release citrus tree fertilizer every 3 to 4 months. Turn the fertilizer granules into the soil around the outside of the pots, to keep the granules off the sensitive tree trunks. Always water immediately after feeding.