Two years ago we decided to extend our growing season by erecting a plastic cover over our lower garden.  Our goal was to be as environmentally friendly as possible and so the 6 x 6 cedar sills which support the frame came from trees in our bush taken down by the ice storm and skidded out with a team of horses. Plants in the polytunnel get their warmth and light from the sun and their water from a spring fed pond via a solar powered pumping system.  The drip line delivers water to the plants without any waste.  The results have been very rewarding.