After your amaryllis (Hippeastrum) has bloomed, it may seem past its prime, but don't throw it away. If you follow these tips, you'll have an even larger plant next year. After it has finished blooming, cut off the flower stalk to 1 to 2 inches above the bulb, and keep the plant, with its long, bladelike leaves, growing through the summer. Around September, place it in a dark closet, and leave it there to lie dormant for a couple of months; this simulates the drought conditions of the plant's native South America. When you take it out of the closet, the leaves will have wilted. Just cut these off flush with the bulb, taking care not to cut any new flower buds that are starting to emerge, and add a little soil if it looks depleted. Water the bulb, set it in a sunny window, and don't water it again until it shows signs of awakening. Your newly awakened amaryllis bulb will grow into a tall, elegant flower, which, if you time it right, will bloom just as next Christmas rolls around.
Martha Stewart Living, November 1997