"Hard" culture is when you grow an adenium under intense light but water and feed it sparingly. This culture results in a more compact and healthier form with shorter sturdier stems, denser leafs and bigger caudices (larger caudex:stem mass ratio).

On the other hand, generous culture can result in weak etiolated growth and shorter caudices. I find that compact adeniums are more aesthetically pleasing.

In their first years, you can "push" adeniums to grow quickly under good growing conditions (= long periods of hot sunny weather, 85+F/30+C)- and get away with it without ruining their looks. But after the first, say, 2-3 years, growth slows down naturally and there's no point in trying to push them further. Shift to "hard" culture, then.

If you can't give your young adeniums and seedlings good growing conditions, don't push them with water and fertilizer. Grow them hard from the beginning.

An example of hard culture under less than ideal growing conditions (actually poor growing conditions): https://www.gardenweb.com/discussions/5071034/adeniums-back-to-bare-bones?n=10

Gill lives in the UK. This is an adenium unfriendly country with cool summers. Not good. But nonetheless, Gill has grown some mighty fine compact adeniums (due to hard culture).