Cold-hardy citrus known for their red-orange fruits, mandarins originated in China. They were once thought to be hybrids derived from oranges, but DNA evidence has established that the common orange is actually a hybrid between the mandarin and the pummelo. Prized because their fruits are very sweet, easy to peel and nearly seedless, many mandarin varieties will produce fruit with seeds when they are grown near other mandarin cultivars. Most citrus cultivars will produce seed, fruit and cloned trees that are genetically identical to the parent tree. But this is not true of mandarins. Trees grown from a mandarin seed may not resemble either parent.
Extract mandarin seeds from mature fruit tree harvested directly from the tree of your choice. Do not remove seeds from fruit you find on the ground, even if fully mature, to avoid picking up soil-borne fungi that may kill seeds and seedlings.
Rinse seeds thoroughly. If you can't plant them immediately, spread them out on paper towels to dry (out of direct sunlight). When seeds are fully dry, store them in polyethylene storage bags in the vegetable drawer of your refrigerator until you can plant them.
Fill the planting pots with sterile potting mix. Plant seeds 1/4 to 1/2 inch deep, then water thoroughly so soil is fully saturated; make sure any excess water drains easily, so soil is not soggy.
Place the pots in a warm, sunny window and keep the soil evenly moist until seeds germinate, usually in about two weeks.
Repot the seedling trees into larger pots when they are about 4 inches tall. Continue to "pot them up" into larger containers as trees grow. Plant them into your garden — or a 20-gallon patio container — when trees are 2 or 3 feet tall. Slowly acclimate them to outdoor growing conditions before transplanting or moving trees outdoors.