Building a greenhouse in Burlington ON. This greenhouse is uncovered from May to October. Then the plastic covering comes down to contain solar heat. Once covered, the inside temperature often reaches 25-30 degrees C on sunny winter days. This warm, fragrant air comes into the house via a fan, as an effective source of heat through March, April, May, September and October. The owner is able to sit out in the greenhouse on sunny days. Cherry tomatoes last until Christmas; kale, lettuce, green onions, chard, chives, thyme, and rosemary last year round. Scroll right in photos below to see the greenhouse being built. The plastic is pulled over a wooden frame, offering an extremely cost effective way to extend the growing season and enjoy the sunshine and warmth during winter.