When to grow peas. Peas are a cool season crop, enjoying temperatures of 13 -18C (55-64F) so they are well suited to the UK climate. Peas can be direct sown outdoors from March to June once the soil has warmed to about 10C (50F).Using cloches will help the earliest crops to germinate.eas are a cool season crop, enjoying temperatures of 13 -18C (55-64F) so they are well suited to the UK climate. Peas can be direct sown outdoors from March to June once the soil has warmed to about 10C (50F). Using cloches will help the earliest crops to germinate.