The popular amaryllis seen in grocery stores and blooming around Christmas is most likely a Hippeastrum. There is a true amaryllis (the A. belladonna), but it's rarely seen in cultivation. Amaryllis is a indoor bulb that grows long, strappy leaves and tall heads of 2–4 lush, colorful flowers. Red and red-and-white combinations are perennial favorites, but they also come in salmon, white and yellow. By staggering their growth periods, or planting many at once in the fall, you can have beautiful indoor flower displays throughout most of the winter. Move them outside during the summer for the foliage phase.
Light: After the bulb sprouts, a tall, hollow flower stalk will emerge. Provide bright light, but not direct sun.
Water: When the flower stalk is growing, gradually increase water. Do not soak bulb. After the flower is done, cut the stalk off and move the plant outside for the summer for the foliage growth. Water freely at this point.
Temperature: In the winter, keep above 60ºF. In the summer, move outside, but not in full sunlight.
Soil: Rich, well-drained potting soil.
Fertilizer: As the flower stalk grows, use liquid fertilizer. In the beginning of the summer, use slow-release pellet fertilizer.
Older bulbs will produce bulb offsets that can be cut off and potted up individually.
You shouldn't have to repot an amaryllis bulb, except to perhaps change the soil every year or so. To do this, gently shake the bulb free of its soil when in its dormant stage and repot into new soil in the same container. When planting the bulb, make sure the top third or half of the bulb is exposed to prevent rot.
Amaryllis grow in two phases: a flowering phase in the winter, followed by a foliage phase in the summer. Near the end of the summer, as the leaves die, gradually allow the bulb to dry out, then move it back indoors when the weather begins to consistently reach into the mid-50s. Rest the bulb in a cool, dark spot without water for a month or two. In late fall, begin watering gradually and a new flower stalk will emerge. You can time the flower cycle based on when you resume watering.