After they have finished their holiday blooming,
To keep the bulbs flowering year after year, you'll have to encourage the bulbs to build energy between flowering cycles.
After the last of the bulb's flowers have faded, it's important to prevent the plant from completing its growth cycle and producing seeds. When the flowers have wilted and the flower stalk has begun to turn yellow, cut the stalk off near the top of the bulb, taking care not to injure the leaves or the bulb itself.
Removing the flowers and flower stalk will prevent seed formation and will encourage the plant to put energy into leaf growth, which will in turn help the plant to store energy in the bulb for the future.
Abundant sunlight is important during this growth phase, so move the plant into the sunniest spot in your house. Water whenever the top 2 inches of soil feel dry to the touch, and fertilize once a month with a liquid houseplant fertilizer, such as a 24-8-16 formula, diluted at a rate of 1/2 teaspoon in 1 gallon of water or according to label instructions.
After all danger of frost has passed in spring, move the amaryllis outdoors to an area that gets at least six hours of sun each day.
If you live in USDA zone 9 or above, where the amaryllis can survive the winter, you can transplant the bulb into the ground, planting it at the same depth as it was in the pot. Continue to water and fertilize as before. When planted outdoors, the bulb will resume its natural growth cycle and begin to bloom in spring instead of in winter.
In colder climates, keep the bulb in the pot and bury the pot in the garden soil. Water and fertilize as you did over the winter indoors. Stop fertilizing near the end of September, and lift the pot and bring the plant indoors before the first frost.
Giving the plant a period of rest after you bring it indoors will begin the process of reblooming. Put the pot in a dark, cool area, and after the leaves have turned brown and wilted, remove them. Allow the plant to rest in this location without watering for eight to 12 weeks.
Check the bulb regularly for the first signs of new growth. When a new flower stalk appears, or four to six weeks before you'd like the plant to rebloom, move the pot into a warm, sunny spot and water thoroughly. With regular water and plenty of light, the plant should produce new flowers within a month.