Salvia patens oxford blue
i have just bought a small salvia patens oxford blue which was a cutting from a nursery. I love the colour and want to help it thrive. The nursery said I should treat it as an annual, that they were hard to keep perennial and were not like dahlias. She said I should bring it indoors during the winter. However, everything I've read online has said to lift and store 'just like a dahlia'. I've got a few dahlias and store them each year so I'm very familiar with this process.
At the moment the cutting is about 9 inches tall, a single stem with a few branches and two flowers. I have potted it up into gritty mpc and put it in my cold green house. How do I best establish and strengthen it this year and ensure it comes back next year? Thanks for any help and suggestions.