I've never seen bonsai not in containers myself. I'm sure folks do grow them in the ground, I've just never seen it personally- I've only seen them in little pots.

I hope your only kidding and not being an A hole. If you know the answer to weather heath and heather can be container grown let me know.

They should be easy in containers with good drainage, but I wonder about them surviving a frozen-solid container in a cold zone. You are planning on these being outside, right?

And I don't know how they would handle all the root-pruning and trimming that is traditionally done with bonsai.

Heaths and heathers can certainly be grown in containers - virtually any plant can. Depending on your location, they may need to be given some winter protection as containerized plants are quite a bit more vulnerable to cold damage than those in the ground.

But I'd have to wonder about the appropriateness of these plants as bonsai subjects. They are low growing, spreading groundcover type plants that only develop a very short (couple inches at most) woody framework at best. Root pruning and trimming is of no concern - they'd handle that well - but the growth habit just doesn't lend itself to bonsai.

Tree heath, Erica arborea, might lend itself to this practice more readily than any other species of heath or heather, but is only hardy to zone 7 so would need to be treated as a tender plant and provided with proper winter care.