None, in an unheated greenhouse. Half hardy plants would need heat if started at this time of year. Hardy ones don't, but you sow those later, around late Feb/early March, either outside or in the greenhouse.

How about sweetpeas? they will grow on, Id grow them on the kitchen windowsill intill they germinate and them move them into the greenhouse.

Scarlet Sage (Salvia splendens) likes cool conditions to germinate, though I don't know just how cool they can stand.

It is too early to start annuals and half-hardy annuals in an un-heated greenhouse. However, it is an excellent time to start perennials though they won't flower for a few years yet.

Thanks all

I plant mine in march, sometimes the middle..sometimes later I go by the weather

Sweat peas, Maggy7 ... I agree, they always do better the earlier you start them. They don't seem to mind the cold at all, though they may not actually germinate for a while. A very small pinch of seeds in a six inch pot, in an unheated greenhouse, will sprout when they are ready. After sowing, cover with a pricked layer of cling film. Thin them out as appropriate. I would keep them in the greenhouse, until they are ready, as they will grow spindly in the warmth of the house. If you are interested in vegetables, then rocket, land cress, lambs lettuce and pak choi are all good for starting at this time in a cold frame environment.