Make a Portable Cold Frame

Make a Portable Cold Frame

An early start to the growing season means fresh organic vegetables are ready sooner.  A cold frame protects plants from wind and help to insulate from the cold so they can get an earlier start.  Here in the temperate climate of the Pacific Northwest, cool season greens can be put out in a cold frame in the winter for a head start, and heat loving tomatoes will thrive under the protection of the frame in the spring.   I have a small garden, so I want to use a cold frame for only part of the year, then remove it during the summer when it isn’t needed.   This lightweight, portable cold frame is easily moved around the garden for successive springtime plantings. 

The design is a modification of the “triangle tunnel” found in the book Cool Season Gardener, which borrowed the idea from the Eagle Scouts.  

Materials you will need

2 each 8′-0″ x  1″ x 2″ cedar boards

1 each 8′-0″ x 26″ clear polycarbonate corrugated roof panel

Stainless steel screws

About 4′-0″ x 3′-0″ of plastic sheeting (like plastic drop cloth), staples and binder clips

How to build the cold frame

  1.  Cut the cedar boards into six 26″ long pieces with a 30 degree angle on each side.  Three pieces will be joined to form a triangle for each end of the cold frame.  Each angle will join another to make a 60 degree angle at each corner, forming an equilateral triangle.

2.  Screw the ends together with one or two screws to form two triangle frames.  The screws are removable in the future if the bottom edge board becomes worn and needs to be replaced.

triangle tunnel assembly

3.  Cut the polycarbonate panel into pieces, each four feet long.  the panel can be cut with heavy duty scissiors.

4.  Attach the panels to the top edges of the triangle frames with the screws.  They are attached at the every other corrugated bend, making sure that the edges at the top of the triangle will overlap.  Once the sides are attached, fastened the two panels together at the top edges of the triangle frames with screws.

triangle tunnel assembly

5.  For an end cover that can be fastened closed or rolled open, attach a piece of plastic cut to the size of the frame.  The plastic is fastened with a staple gun at the top edges.  The bottom edges are clipped closed with picnic tablecloth clips.  Even when the end is closed, there will be some ventilation through the open spaces in the corrugated panel edges.  More ventilation is possible by rolling up the plastic ends and clipping to the frame sides.

triangle tunnel frame

6.  Anchor the frame down with tent stakes and twine to keep it stable in the wind.

Where to go for tools and workshop space

This project was put together with the help of tools found at the Seattle Capitol Hill tool library.  The useful (and sometimes unusual) assortment of tools, with the help from the friendly volunteers, were all I needed to accomplish this project.  Should I use a chop saw, band saw, miter saw?  I tried them all right in the shop. 

The tomato plants love it

tomato plant in a-frame triangle tunnel cold frame

The cold frame keeps the tomato and cucumber plants protected from wind and constant rain in the still chilly month of May.  They like warmer temperatures and the cold frame makes a difference of just a few degrees that helps them to grow faster and stronger.  They will soon grow too tall for the frame and be ready for summer!

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