For Huernia plants it’s important to use a well-draining soil mix. Something like 50% pumice/perlite, 25% peat/organic mulch and 25% sand mix. A cacti-succulent mix would suit. This helps to prevent over-watering and root rot.
Make sure that in winter and fall they’re not exposed to anything colder than about 5C and that they’re kept very dry, as they will go dormant and their roots will die back.
As in nature they normally grow underneath other plants or shrubs, Huernias grow well in partial sun or bright shade. They will take full sun as well though they may burn in extreme temperatures.
They can be amazing when planted in a hanging pot and if left to run and well cared for, they can grow to almost 120cm long. That’s almost 4 feet!