I have a diamantina clematis in a pot on a terrace facing west.
This is it 2nd year. It flowered beautifully late spring/early summer and it has not flowered again. There are no buds appearing yet .
It did flower twice last year. Is there anything I can do to help it flower again. I did fertilize it every 2 weeks.
If the plant is otherwise healthy, don’t worry. The second flush of flowers for this type of clematis takes place in late summer or early fall.
I would cut back on the fertilizer. Excess fertilizer, especially one with a high nitrogen content, leads to lots of leafy growth with few blooms. Every two weeks is a LOT of fertilizer.
You didn’t mention that you pruned the vine after the first flush of flowers, which should be done.
Here is a detailed response we provided to another gardener with the same question: https://www.torontomastergardeners.ca/askagardener/diamantina-clematis-not-blooming/
And for a detailed description of this plant’s growing habit and requirements, including pruning instructions, see https://www.gardenia.net/plant/clematis-diamantina