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Cold Frames

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September 4, 2019

We are finally enjoying cooler temperatures and vegetable growers want to extend the season today on Southern Gardening. 

Cold frames are great tools for extending the growing season, especially for veggies grown in containers.  They act as a mini greenhouse and protect your plants like a large cloche. 

You can go high tech with insulated walls, sink the foundation into the soil, add heating cables for the floor, and a double pane top can act as a mini greenhouse. 

Used recycled windows are also good choices for the cold frame top.  Or try using a clear plastic window well cover that could accommodate larger plants. 

You might like a little flexibility and not want to have a permanent cold frame.  Portable cold frames can be built very easily.  Using hay bales for the sides and a pane of glass for the top is a very effective low tech version.  Commercial version of portable cold frames are also available. 

If you decide to use a cold frame consider these tips to get the most benefit.

  • Orient the cold frame in an east to west arrangement and make the south side lower.  It will absorb more solar energy. 
  • Paint the inside surface white to reflect sunlight back onto your plants. 
  • You will need to vent the cold frame.  Heat will build up quickly during the day.  The highest temperature shouldn’t go over 80 degrees. 
  • Venting will also reduce dampness and keep foliar diseases at bay.  There are thermostatically controlled vents as well as bi-metal automatic hinges.  These are great if you work and can’t be there to open and close the cold frame. 
  • Be sure to check for air leaks so the precious warm air doesn’t escape at night. 

I’m horticulturist Gary Bachman for Southern Gardening.

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