In my limited experience, my clivia seem pretty hardy (zone 10). Even in shadier spots, we have had a lot of rain this year and my variegated one and several others just put out a spectacular bloom.

I think it's best to let their soil dry out a little before watering, especially when they are not in flower. Many S. African plants flower during winter rains and need little or no water in the hot summer months. While clivia don't go dormant, keep summer water to moderate amounts.

Mine are outdoors and tolerate sun, but the leave tips have burned in high heat. In the summer I would put it out somewhere where it gets some morning sun and fresh air.

They aren't super fast growers, so that may not be the best measure of their thriving.

All but one species of Clivia are native to wooded areas (dappled to full shade) in the Eastern Cape where rainfall is concentrated in the summer. The one species that is native to a winter rainfall region is not available in the nursery trade yet.

Clivias are NOT hardy below 35F! Other than that they will come back from considerable abuse. They prefer damp, but not soggy Summers and 6-8 weeks of nearly drought conditions in early Winter.