Using Cold Frames at Michilimackinac Posted July 9, 2021 Gardeners, especially at the Straits of Mackinac, have always been interested in helping their plants grow despite sometimes problematic environmental conditions. Building walls or planting hedges can protect plants from the wind, which might break fragile stems and leaves, while changing the soil chemistry with manure or compost can make a poor soil rich enough to grow the sweetest melons. But what about the cold? How would gardeners in the 18th century protect tender plants from the snow and frigid temperatures so common in northern Michigan? Cold frames may have been the answer. Our gardeners at Colonial Michilimackinac have recently been generously gifted with a very nice cold frame. Built using 18th century specifications, it is essentially a miniature greenhouse. Pots of plants are set inside the frame, or seeds can be planted directly in the soil to get off to a good start in the small, protected environment. The wooden frame is topped with two glass “lights” or windows that can either be kept closed in cold weather to trap heat, vented to release moisture, or completely removed to allow for air flow on sunny and warm days. With a bit of work, a cold frame can even be used to generate heat to keep young plants warm and healthy. Historically, frames were placed over brick-lined pits full of animal manure. As the manure decomposed, it released heat, keeping the inside of the frame warm enough to support lettuces, spinach and other cold season vegetables throughout much of the winter, or at least late fall and early spring. Modern gardeners use electric heat mats to produce similar results. If you are interested in see our new cold frame and learning more about the gardens and the people that lived at Colonial Michilimackinac visit mackinacparks.com for tickets and more information.