Which Amaryllis variety is the hardiest?

There are two types of Amaryllis, Hippeastrum and Amaryllis Belladonna, and both are fairly hardy and come in multiple varieties. According to the Fred Spicer from the Birmingham Botanical Gardens, no other hybrid or species is hardier than Hippeastrum × johnsonii.

Hippeastrum are known for being almost evergreen and blooming indoors even in winter, while Belladonna is a summer flowering plant which typically blooms year after year planted outdoors. The Hippeastrum sonatini "Ballentino" produces red flowers with white highlights and can be planted both indoors and out.

Hippeastrum and its hybrids make excellent garden and potted plants. Most varieties will last through spring and summer and bloom in winter. Some outdoor versions can even withstand mild frost.