Season extenders like cold frames and row covers are tricky ways that can stretch the growing and harvesting seasons. In regions with short growing seasons, the difference of even a few days can mean the difference between a bountiful harvest and no harvest at all for vegetables and a jumpstart for flowers, too.
Any season extenders that are smaller than greenhouses are meant to give you a few extra weeks of season, not months. "Plant protectors" come in many shapes and forms, from full row covers that extend down an entire length of the garden, to waxed paper "hot caps", water jackets, or even recycled plastic milk jugs. They are set in place over newly transplanted plants and help to warm the soil and protect the plants from a few degrees of frost.
A cold frame is a simple, unheated structure that uses the power of the sun to warm the interior and get plants off to an early start. Most cold frames are made from lumber and are built so that the back of the frame is higher than the front and the cover slopes downward, facing the sun. Recycled windows and glass-front doors make great cold frame covers and the frame can be built to fit their dimensions. They don't have to be fancy, just functional. Cold frames are great for getting a jumpstart on the season, and early crops of lettuce and spinach can be grown to maturity in a cold frame while your neighbors are still waiting for the snow to melt.