Cold frames need attention and perform best when kept cooler, rather than hot. For example, keep the temperature inside below 60°F to 65°F for cold weather plants that grow best in spring or fall, and under 75°F for other warm weather plants. Be sure to prop the lid open when needed to help regulate the temperature. Place the lid back on tightly to keep the interior warm. When below freezing temperatures hit, pile extra insulation such as blankets, newspapers, or straw on top of the glass. Snow is quite heavy and can sometimes break glass, so no matter when you are working with, it will need regular attention to optimize plant growth.