The varieties of Clematis tangutica, such as ‘Bill Mackenzie’, are much more widely offered than this, the species. The general cultivation advice for most clematis, is to grow it in fertile, humus-rich, well-drained soil, with the roots and base of the plant in shade. Here’s this one growing out of the stone wall with no soil at all, and its roots in full sun! It doesn’t grow huge, but it produces its bell-shaped yellow flowers prolifically; the fluffy seedheads which follow are more striking. C. tangutica is a Group 3 clematis, needing pruning in the early spring, so as to produce the new growth such as it is flowering on now. I prune it almost to nothing.