Question: I would like to continue growing some vegetables over the winter, and I am hoping I can start my seeds earlier in the spring. How can I construct a simple cold frame and maximize its use this winter?

Answer: Cold frames can be used to extend the growing season, grow certain vegetables throughout the winter, protect tender herbs during freezing weather and enable a gardener to get a jump start on starting seeds for spring. All that is needed is an enclosed structure with a translucent lid that gives the plants protection from wind, rain, and to some extent the cold temperatures.

A cold frame works as a miniature greenhouse and there are a few different types you can construct: sunken cold frames using cinder blocks and a rigid plastic top, mini hoop houses, hinged hoop houses and portable wooded frame houses with rigid plastic covers or lids are just a few. Cold frames are often used in conjunction with raised beds. When considering what type of cold frame you are going to build with raised beds, location is very important. Some structures are lighter than others and may not be appropriate for windy areas or may need to be secured to the bed itself, making them less portable. Also consider the amount of snow you typically get in your area. You want to choose a structure that can stand up to the weight.

Portable framed houses are usually made from wood with the back of the structure slightly higher than the front, allowing the sun to be captured. The lid can be made from old window panes attached by a hinge. If made from wood all surfaces should be protected with a coat of exterior paint, preferably white to help reflect the sunlight. Hinged hoop houses are made with a combination of wood, flexible PVC pipe and plastic sheeting. They can be single or double walled for extra insulation. Alternatively, mini hoop houses can be built over rows of vegetables without a raised bed. The frame can be built completely from flexible PVC pipes or you can use a heavier material to build a frame. If they are not hinged, giving the ability to open and close the structure, the walls will need to have the ability to be rolled up to give ventilation and access to your plants. Place the cold frame over your garden bed and orient it to the south to trap the maximum amount of heat and light. Sunken cinder block or brick frames are more permanent frames. Sinking the cold frame slightly into the ground will provide added insulation.

The temperature inside the cold frame will fluctuate according to outside temperatures and sunlight. On sunny days the inside of the structure can get quite hot. The temperature must be able to be regulated by opening and closing the lid or rolling up the plastic sides of a mini hoop house. Ventilation should be closed by late afternoon to retain the heat accumulated during the day. On cold nights extra insulation can be required such as an old blanket or layer of straw.

Cool season crops such as lettuce, cabbage, spinach and radishes will thrive with daytime temperature hovering around 60 to 65 degrees. Nighttime temperatures should be 5 to 10 degrees lower. To germinate seeds, daytime temperatures should be 70 to 75 degrees. The soil should be kept moist at all times but not wet. Watering in the morning is preferable so plants have a chance to dry before nighttime.

For those gardeners who wish to garden during the winter months, a cold frame is a simple way to bring fresh produce to the table and satisfy the urge. It also gives you that head start in spring, with plants ready for transplant into the garden as soon as temperatures allow. In the summer, your cold frame can be used to dry herbs or onions and garlic by laying them on racks inside the frame.

For more information on constructing cold frames, contact your local extension office. Atlantic County residents can contact 609-625-0056. Cape May County Residents can call 609-465-5115, ext.3607.

Interested in becoming a Rutgers Certified Master Gardener? Classes in Atlantic County are forming now. There is still time to sign up! Classes begin on January 7 and run on Tuesday mornings at the Rutgers Cooperative Extension office in Mays Landing. Applications are available on our website at Please call 609-625-0056 for more information. Cape May County residents welcome.

Do you have a gardening related question you would like answered here? Please forward your questions to Belinda Chester, Master Gardener Program Coordinator, Rutgers Cooperative Extension Office, 6260 Old Harding Highway, Mays Landing, NJ 08330. You can also submit questions at or email them to; please include “garden question” in the subject line.

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