How to Winterize Your Urban Garden, Part Two (Cold Frames)

Today I’m thrilled to introduce a series of posts written by Patricia Youngquist AKA The Last Leaf Gardener. This is her second post in the series on winterizing. Be sure to check out her introduction to winterizing, and stay tuned for her post on how to wrap your plants. And now, I’ll step aside and let Patricia tell you about cold frames…

For a couple of the past winters, I protected my less hardy plants, shrubs and herbs from harsh elements by constructing a cold frame. I had learned my winterizing lesson the hard way, when some years ago, I bought my “less hardy” perennials inside my studio apartment only to have them die from shock and the dryness of my place. The dryness is caused by steam-heat – a bane of existence to many New York City dwellers. These conditions did not make a good atmosphere in making a winter home for the less hardy things that I love to grow and the things that remained outside during that year were not too happy either.

In any event, the experience of having my plants and herbs die is behind me, thanks to my having used a cold frame. A cold frame is a transparent-roofed enclosure usually built low to the ground and used to protect plants, herbs, and small shrubs from cold weather. The transparent top of a cold frame admits sunlight and so the structure functions as a miniature greenhouse. It costs nothing to use because it relies solely on the warmth of the sun.

Cold frames are generally found in rural home gardens, but because I live in Manhattan, I have become quite creative in making use of space. I saw no obstacle in having a cold frame constructed to use during the winter months that could be taken down and stored during spring, summer and fall. Normally a cold frame is constructed with old glass windows and wood, but I used Plexiglas, and 4x4s for the corner posts as well as 2x4s for the additional framing. I chose these materials so that I could take the cold frame apart and store it – without fear of it breaking – in my closet during the non-winter months. The minimum thickness needed for Plexiglas used in this manner is 1/2”. I used five pieces (4 sides to form a square, and one for the top that functioned as a lid). When determining the height of the sheets of Plexiglas, I had to allow for several inches of empty space above and around each plant for air circulation, so in my case my cold frame looked like a mini-greenhouse.

Usually a cold frame functions optimally when it is butted up against a home, garage, or solid fence, but with roof-extension gardens these options are usually not available. The first year I chose the part of my roof-extension that received the most sunlight, and I recommend anyone taking on this mission find the sunniest spot on their outdoor space to place a cold frame. Extra humidity can be provided by placing trays – that are similar to those that are used in a darkroom as developing trays for photographic prints - filled with bark chips or mulch and put underneath the plants.

Additionally, I also needed to make sure I allowed for the lid to be able to be left open – at least a few inches – so that the air could circulate from time to time. (I used a bamboo pole on days I wanted to keep the frame open). I made my plant’s winter home festive by adding and placing little window boxes of hearty plants alongside the outer edges of it.

My plants and herbs did well in terms of warmth that first “cold-frame” year, but the second year I put the structure closer to the walls (as seen below) of my apartment to protect the plants, herbs and shrubs from wind-damage, and in addition to the lights and window boxes, I draped it in garland for the holiday season (as seen below). The SODAS sign is an object I had in my garden from the late 1990s until this past spring and I am merely pointing it out to you for a sense of scale.

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If you’d like to see more pictures of Patricia’s garden, please visit her at www.thelastleafgardener.com. You can also connect with her on Facebook or Twitter .