winter cropping potatoes

I would plant them at the bottom and gradually add soil / compost as they grow in exactly the same way you can grow 'normal' spuds in pots. They will need to be kept watered and protected from frost later in the year. Feeding would be a good idea as they are hungry plants

I'm going to do the same this year to have Christmas spuds then an extra early crop planted in Feb..  As I've never grown spuds before it is all new to me.. But i'm a fast learner!!   

How would I protect from frost in my unheated cold greenhouse which is on top of my flat garage roof tucked alongside my house wall... it is sligthly sheltered on 2 sides from wind..

I also have another normally situated at the bottom of the garden and is protected from wind but it is shaded from afternoon sun by a rather high hedge... not that we get much sun in winter!!

Both these will a combination of spuds and winter onions. I'm not worried about protecting the onions as they and the pots always freeze up in winter and I take them out when the warm days start... then the just grow quickly..