For help, we used one of the 3 techniques below.
For the green onions we use the double-covered bed technique. The onions are situated in a cold section of the garden and we want to keep the temperature near the ground higher than under a cold frame or row cover. With a double coverage, it can be possible to grow half-hardy to hardy vegetable all winter. The greenhouse is about 3’x 4’ and cost me less than 30$ (2010) in material.