The secret to getting amaryllis bulbs to rebloom year after year
lies largely in summer care after flowering. Remove the faded
flowers and stalks as soon as they are finished blooming, but do
not cut off the leaves. Set the pot on a sunny windowsill and
water as needed. When warm weather arrives and all danger of frost is passed, set the bulb, container, and all in the
flower garden. Choose a location that is somewhat protected
and receives morning light. You can set the pot in the ground so
that the rim is at ground level.

During the summer, continue to water the plant as needed and feed it every two weeks with a soluble houseplant fertilizer. Gradually withhold water before freezing weather in the fall. When the foliage has died down, trim it off and take the pot to a cool, dark basement (40 to 50 degrees F if possible) and place it on its side. The bulb needs to sit and rest for six weeks before you try to rebloom. Because it takes approximately six weeks from planting to bloom time, you can decide when you want the bloom to occur and then count backward to determine the planting time. During the rest period, do not
water the plant. As the leaves dry, cut them off.

For additional details refer to: Reblooming Amaryllis.