The ideal time to dig up, divide and replant amaryllis bulbs is early to late fall, when the foliage naturally withers and the plants become seasonally dormant.
Slice no closer than 6 inches into the soil around the bulbs. Unlike tulip or daffodils bulbs, amaryllis retains roots. Try to retain as many roots as possible while digging and dividing. Punctured or cut bulbs usually rot when replanted.
If amaryllis bulbs multiply and become overcrowded, flowering may diminish. Make sure, when dividing and replanting the bulbs in fall, to plant them so the tip of the bulb is right at the soil line. Don't plant too deeply.