People living in cold climates especially in Northern Europe and North America are so cold most parts of the year that they cannot grow anything and have to survive on imported or stored food. While there is no easy way to fix the lack of fresh veggies and salads, you can try this technique to grow home made veggies and use them all year long. Greenhouses are often used in areas like these to house plants and flower parts away from the bitter cold. But, they cannot provide the warmth through the long night. A much better alternative to traditional greenhouses is the South American concept called walipini which is essentially an underground greenhouse. The greenhouse uses a combination of the greenhouse effect, insulation and passive solar heating to maintain the temperature inside of the hole.
It was developed almost 20 years ago in the mountainous regions of the continent and has since become very popular with the poor populace in providing useful produce through the cold months. Here is the cool video on how to get a walpini up and running: