Here's what I learned about growing caudex plants like Adeniums that evolved in hot, dry deserts. If you can't duplicate their natural growing conditions, your plants will not grow at their full potential. It's that simple. Your climate zone will have little influence, except if you live in a desert, and your growing conditions match the desert climates that are found where Adenium grow naturally. Do whatever you need to do to duplicate the deserts where this plant evolved. Light, the substrate, quantity and frequency of water at the roots, drainage, all need to be carefully controlled by you.
Full sunlight exposure, every day. Full heat and warm dry nights throughout the year. Drying winds, especially if leaves get soaked by rains, little water at the roots except if plant is actively growing in full sun and heat. Little fertilizer, and use organic slow-release ferts. when you must. High nitrogen formulations like Miracle Grow, will push leafy, weak, soft, lush, growth that can easily rot. Plants are more disease resistant if grown "hard".
These desert-growing, water-storing plants are tough, and will fail if pampered. Many of the You-Tube videos show beautifully grown Adeniums that are grown by professionals, under ideal conditions. Canopies full of leaves, loaded with flowers, plenty of branches, thick spreading roots, etc. take years of careful training, pinching, branch wiring.....
Also know that containerized plants are not growing naturally. The roots are restricted, and the growing medium can become dangerously hot in full-sun exposures and stress or cook the roots, Take precautions, and try to keep root zones cool. Quick-draining grit loaded mixtures allow water to just pour through, and pull fresh air into the root zone. Peat, and sand loaded soils retain too much water that soaks roots, stagnates, then rots roots. Leaves turn yellow.... blossoms/leaves drop. Plant eventually fails.
Georgia can be hot, sticky humid, and rainy. Not exactly a hot, dry desert. But you must provide the right growing conditions that will "fool" your plants. I also live in zone-7b. I grow my plants in full sun, on my back deck, planted in mostly coarse grit, crushed oyster shells and some small chunks of pine bark. The organic component probably is less than 25% of the total volume. Water and rain pours through the drainage holes, and the medium dries out very quickly. So far, my plants bloom, and are still alive. But now....my nighttime temps are starting to hover around the 50s. If I don't move my plants into the house at night, they'll shut down, drop all leaves and go into dormancy. They grow actively from May-June thru mid September. Not exactly the deserts of Namibia. This year, my plants will go under high-intensity 600W CFL lights in an effort to extend the growing or non dormant season as long as possible. Will it work? I don't know. But I'll tell you this: my plants spend more time in dormancy than they do actively growing. Not good. But try, I must. Know also, I'm used to killing plenty of plants, over the years. It happens.
Seeds: Same advice. Heat, full-sun or very bright grow-lights a few inches away from the leaves. You-Tube videos will give suggestions. Also....seeds will not duplicate the parent plant. Don't fall for the trap. Seed sellers want to sell seeds, and they could care less if you're fooled. They got your seed money. There are some reputable hybridizers that are selling high-quality, hand-hybridized seeds, but even then, you'll probably grow hundreds of seedlings before you get a plant that has blossoms like looks the parent. It's a total crap-shoot, and seed sellers are full of crap if they claim their seeds will produce blossoms like the parent. It's not gonna happen....and btw, there are no bright blue Adenium blossoms...yet.
Don't be daunted. Adeniums are difficult to grow well. Read thru the forums and look at all the problems that growers are discussing. All, can usually be solved with correct culture and better, growing conditions. Match the desert climates and you're 90% there.
Hope this might help. Keep trying, despite some failures....and check your cultural conditions.
Good luck and happy growing.