Citrus trees can be grown easily from seed with a few basic supplies. However many types of citrus are slow to produce fruit, especially orange trees. According to horticulture professor James Ferguson with the University of Florida Cooperative Extension Service, Mexican and key limes usually produce fruit within two or three years, which is very fast for citrus trees. Other varieties worth considering are the Orlando tangelo and Dancy tangerine, both of which can bear fruit within four years.
Fill your planting tray with sterile potting soil and add enough water to moisten the soil. Be sure to use a planting tray with drainage holes in the bottom or add them if needed.
Remove the seeds from a store-bought citrus and wash them immediately in lukewarm water. Put the seeds on some damp paper towels to keep them moist. If citrus seeds are allowed to dry out before planting they will likely not germinate.
Push the seeds gently into the cells of the planting tray to a depth of 1/4 to 1/2 inch. Place the planting tray into the plastic bag and seal it to maintain humidity.
Find a warm location, preferably around 80 degrees F. The top of a cupboard or cabinet works well since most rooms are warmer towards the ceiling. Check the moisture content of the soil every two days and add water if needed. The soil should always be moist, but not wet. Most of the seeds should germinate and produce sprouts within 14 days.
Remove the tray from the bag as soon as the seeds have sprouted and place it in a warm spot that gets direct sun. A south facing window is ideal. Continue to water as needed and leave the sprouts in the tray until they have developed at least two sets of leaves. Citrus seeds can produce up to three sprouts, two of which will grow quickly while the third languishes. Remove the straggler sprout by pinching it off as only the stronger two will produce trees identical to the parent.
Transplant the seedlings to 4-inch planting pots filled with regular potting soil. Continue watering and keep the seedlings in direct sunlight.