The simple answer is you don't. They naturally grow over winter as cool season perennials where hardy (z8-10). It is likely that what you propose won't work, this is why people aren't growing ranunculus in every garden. They just don't work.

They are triggered to bloom by lengthening days, and have to have the foliar mass to support the bloom. That means they need to be started in fall to achieve the critical mass to support bloom. Started in spring, they won't make it.

Agree. Can't even grow them from corms reliably here!! They are often offered as early spring planted starts, often with buds and blooms, and will last until the weather heats up. Suggest that might be the best way to include these in your garden. If conditions are right, they could make a return next year.

I planted some ranuncula corms last spring in fairly large wooden planters (1 cubic foot) with the intent of over wintering them where they wouldn't freeze. They came up but did not flower last year. I am waiting to see if they survived and/or will do any better this year. The real test will be deciding when to move their planters outside again. Where they are now (indoors/unheated) will probably get too warm for them in March but it will still be too early to move them outside until mid-April. It will be a challenge.