have just ordered some big pots so that we can grow some stuff in the greenhouse over winter. My question is should I fill them will soil from the plot, compost or a mixture of the 2 and how often should I change it?

Before allotments I grew potatos in square plastic flower pots in the front garden, use cheep grow bags, no wiggly things etc. came out nice and clean. But did not grow anything over winter

Depends what you want to grow !! Info pleasse !!

The main one we want to try is carrots but I was also thinking dd could grow radishes and other such things in them. As I say nothing set in stone yet

I'd say deffo use soil from grow bags

Carrots like lots of moist sand ! Lettuces would appreciate some compost, makes for lush growth, radishes will grow in anything!!

Thanks for your help guys

How often should I change it?

I revamp the soil in my tubs and pots every year !

That's what I thought, just wanted to check Thank you

Yep, agree with what everyone else has said I'd just add that I certainly wouldn't just use soil from the plot on its own because unless it is very very sandy soil, it'll probably not have enough drainage and the pots will become waterlogged

Growing stuff in winter is tricky indoors due to low light levels leading to damping off (thinking unheated greenhouse here) You might be able to do some spuds. I've done carrots outside overwinter quite successfully and spinach and lots of winter lettuces