Blue poppies probably would germinate at 55ยบ F, but take a bit longer.
They can be grown as a winter sow, but here they are too small then.
I use the area near the windows of this old house-it is always cooler there.
I place cheap 'frig thermometers throughout the house so I know where it is warm and where it is cool.
Most plants for an ordinary rock garden can be grown from seeds.