I have had many, many Crinum bloom in pots here in zone 6 outside of Pittsburgh without problem. This goes for the few hybrids I got in trade many years ago and also many of my rarer species from South Africa, Madagascar and India. The easiest species to grow and bloom every single year is C. amoenum from India for me, but others bloom almost as reliably. Best of luck :o) Dan

I've had C. bulbispermum & variabile flower for me in pots every year. 5 gallon pots & lots of water & fertilizer. Winter them indoors (in their pots) in a dry cool spot.
I've also the same two species outside and overwinter them with 6" of straw and as much snow as I can shovel from the driveway....they've both bloomed as well.

I have permanently in-ground crinums here in metro Detroit, they've been there close to 15 years now, large clumps that bloom well each year. I just dump about a foot of leaves on them in the fall after cutting the frosted foliage to the ground.