Cold Frame Extravaganza!

We began our Freedom Gardens pursuit with a goal-in-mind to extend Montana's growing season, which is May 1st to September 30th. One concept in particular drew our attention - Elliot Coleman's technique of covering produce inside a hoop-house for added protection, known as double covering. We hypothesized that a similar method of double covering could be achieved with the use of cold frames.

                                                                                                                                              

We knew we wanted a frame deeper than the one featured in the previous blog posted by Chris below, but were not quite satisfied by the dimensions set forth by Elliot Coleman - 8 to 12 inches high in the back, and 6 to 8 inches high in the front.  We decided to make our prototype dimensions

The prototype

21.5 inches high in the back and 9.5 inches in the front, with a distance of 4 feet between the front and back and 6 feet from side to side. When the cold frame was completed, we stepped back and critically analyzed.  We were still concerned about the height of the box - our thought was the taller the lid, the taller the plant could become.  We also figured we could gather another 6 square feet by adding a one foot ledge to the back of the box.  Our final adjustments led to a 12 inch front and a 24 inch back with a 5 foot depth and 6 foot width for 30 square feet of growing space per box.

When it comes to building, nothing substitutes a well thought-out drawing.  When we decided to build cold frames, every step was drawn out prior to action.  Fortunately, Mark E. possesses some impressive graphic skills, which turned our mere sketches into works of art!

Cold Frame Template - We followed these dimensions near exact with the exception of increasing the front and back box heights to 12 and 24 inches respectively.

The other rather important aspect of building, is calculating exactly how much materials you need to acquire in order to succeed.  Interestingly enough, our story began with a craigslist add - a third party was purchasing polycarb in bulk and offered the bulk discount to anyone interested.  In a few weeks, we obtained four 16 ft by 6 ft sheets of triple-ply polycarb.

Triple-ply polycarb sheets

Since we knew the dimensions of our boxes, we quickly went to work cutting the sheets down.  This was done easily with a circular saw,   a many toothed blade, and patience. We were now ready to build the cold frames.

The cold frame construction took place in three parts - joists, on site formation, and lids.

The joists were key to the cold frames.  After cutting the polycarb sheets down, we had 16 total lids.  One lid was dedicated to the prototype, so we knew we were going to place 15 cold frames on the fairgrounds.  We also realized that creating a continuous flowing cold frame vs. singular individual cold frames would save materials.  Given these points, we calculated that we'd need 19 joists in total. Once the joists were pieced together, we transported them to the fairgrounds.  Another time saving point worth mentioning, is to have your local lumber company deliver the necessary lumber to your work site!

Prior to delivery of joist and lumber to the fairgrounds, the site itself was greatly modified. Together with fairgrounds staff, we removed approximately 3 feet of existing soil   strata, and replaced it with top soil.  We tested the top soil prior to placement to assure the quality of the soil.  We then leveled our location to the best of our abilities with machinery and rakes.  The last order of business was to mark the exact areas where the cold frames were to be built.  We decided to angle the boxes approximately 30 degrees west of south in order to optimize evening sun capture.  We believed this would be necessary given our potential for extremely cold winter temperatures.

Site prior to construction

With the site prepared and the joists pre-constructed, building the cold frames themselves went pretty darn fast.  We began by placing the joists approximately 6 feet apart and then pieced them together using 12 foot 6 by 2s.  We alternately placed the 6 by 2s to increase overall structure stability.  The end walls were created with vertical placed 6 by 2s cut to match the final joist angle.

Cold frames without lids

At this point, we utilized a six foot level to make the frames as level from end to end and front to back as possible.  We then piled excess soil against the front, back, and sides of the boxes.  The next step to the building process was the lids; however, due to the timing of cold frame construction - late spring - we decided to plant the boxes and lid them at the end of the growing season.  We'll discuss the 2013 growing season and lessons learned in a separate blog post, so stay tuned.

To construct the lids, we utilized stacked 1 by 4s.  By stacking the boards, we were able to create a solid cross member while sustaining a rigid outer frame.  To further rigidity, we included wood glue in addition to screws. Once the
frames were constructed, we were ready
to attach the polycarb, or so we thought.

Recall our desire to include Elliot Coleman's double covering technique.  Well, our first intention was to simply lay shade cloth on top of plants in the evenings so as to decrease radiant heat loss at night.  The theory seemed sound, but we wanted to decrease the amount of times we needed to visit the site each day.  We instead decided to attach shade cloth on the inside of the lid frame while the polycarb would be attached on top or outside of the lid frame.

Lidded cold frames

Inside the lid

To begin the process, we laid the lid frames on top of the cold frames, lined the two up accordingly, and attached hinges. Once the hinges were attached, we were able to open the lid and attach the shade cloth.  We used staples to attach the shade cloth; however, we were concerned that the staples would simply tear right through the cloth, thus we utilized thin wood slats on top of the cloth and then stapled through slat and cloth into the lid frame.  Once the shade cloth had been applied, we were able to close the lids and place the poly carb.  With the lids attached, we were ready to see just how far we could stretch the growing season into a Missoula, Montana winter.  We're hoping to invest in a few logging temperature readers in 2014 to obtain and share temperature data with you - stay tuned!