Cold Frame Construction
Posted by: TammyLast year, I experimented with cold frame construction. My first cold frame was VERY simple with straw bales and two recycled slider doors (from a friend’s house remodel). It was a big success, giving me lettuce, spinach and radishes well into winter! In the early spring, the apparently dormant spinach and lettuce began to take off with incredible enthusiasm, well established and happy, creating huge heads of lettuce and spinach!
The only issue I had with this simple cold frame was accessibility. It wasn’t easy tipping the front slider so I could access the produce. It was a spring Nor’Easter that spelled doom for my first cold frame. The wind tipped the front slider and it fell against the stone retaining wall, shattering into thousands and thousands of pieces. It took my four hours to vacuum up the pieces with my husband’s garage vac (and 3 cords to reach the garden). Although I loved the concept, I had to make a more secure cold frame.
We went to the web for some cold frame research. Mother Earth News also had some great suggestions as well as my Country Wisdom and Knowledge book (EXCELLENT book for so many things related to country life-a MUST HAVE in your country library).
We ended up combining the plans from several sources to create out cold frame. The biggest thing we had to have was the glass for the top. We had to replace our sliding door last winter because of some rot and replaced it with a more energy efficient slider. This provided up with two large, double-paned sections of glass. The cold frame dimensions are that of the sliding door, about 76″ by 36″.
Here is a picture of the completed cold frame: Ummm, excuse the photographers shadow 
I’ll explain how we did this but it’s by no means, an exact construction plan. Truthfully, we had to wing-it in some areas of construction, trying to utilize what we already had in order to keep the cost down. What you use for your glass will affect the plan, too. If you just had old wooden windows replaced (or have a source for some) and you’ll be using two or three windows instead of a huge sliding door, the measurements will be different. You could also just go with plastic for your ‘window’ and so measuring isn’t so critical (it isn’t as insulated but it would work) So again, this will give you a construction GUIDE, NOT a plan.
Our supply list included:
4″ x 4″ posts (will vary if you build your base higher than we did)
One- 2″ x 12″ pressure treated board (14′)
1″ x 3″ finished pine strips (to reinforce the frame of the sliding door)
weather-resistant screws
2″ x 4″ to reinforce the back wall
landscaping spikes (some people use rebar to stabilize the 4 x 4s )
protective sealant for the finished pine strips (I used Cabot preservant/oil )
Hinges for the top
Because of the size and span of the sliding door, we decided to reinforce the frame work of the sliding door (to prevent torquing which might cause the glass to break and sagging which would also stress the glass). If you had smaller windows with solid frames, you might not need this. I sealed the finished pine strips first so they’d have time to dry.
Part of this project began last winter when I observed the sun through the season. I had to be sure that my cold frame location received ample sun throughout the day and winter. I had created a hoop house for one of my beds but observed that that area of the garden received almost no sun through the winter. The area never warmed up. This is such an important part of the process. Here you can see the completed cold frame up on the hill over the garden at around 11:30am. It’s in full sun and stays that way for nearly 6.5 hours each day.
This picture also shows the angled face of the cold frame which allows ample sun into the frame.
I decided to dig into the hill side and place part of the base below ground level on the back side and the sides. This would insulate it from our cold CT winters and provide a level building area.
OKAY-CRITICAL POINT! MEASURE TWICE or three times, or maybe even four before you start cutting! We had the sliding door measurements and had a plan with measurements so we began by cutting our 4 x 4 timbers and creating the boxed in base. We had landscaping spikes already (from previous projects) and used those to tie the timbers together and then anchored them into the ground. We pre-drilled the holes for the spikes.
Here is the box coming together and my husband pre-drilling the spike holes. You can see how I’ve dug down into the ground to create the level building area.
Make sure you make your base level from the first timber. If you don’t, things only get worse.
Once we had the boxed in base done, we focused on the door reinforcement. The biggest thing was making sure we knew where the glass was within the frame of the slider. We didn’t want to screw through that! We pre-drilled the holes for the screws on the door. This picture shows the hinge but it also shows how the sliding door is sandwiched between the 1 x 3 stripping.
Here is the outside corner (notice the ADT sticker still on the door-won’t the chipmunks and squirrels be afraid of our ADT secured cold frame LOL! )
There is a 2 x 12 on the back wall of the cold frame and then we used 2 x 12′s that had to be cut on an angle to close in the sides. We also attached a 2 x 4 to the length of the front of the box that the door rests on (under the handle area) which gave use a big less of an angle cut on the sides. My husband measured two points on the side, with the door balanced in place by me, and then basically connected the dots to create the side angle cut. Again, measure, measure and measure again!
Here is how we ended up creating a solid connection between the base and then the back wall:
You can see the 2 x 4′s that run all the way to the ground. They are screwed into the boxed in base and then we were able to attached the back wall 2 x 12 to those. Then, the side walls are screwed in from the back of the 2 x 12 back wall. You can see that angled side wall here:
We used two heavy duty hinges (previously seen) to attach the door to the back wall.
Although we considered ‘fancy’ supports for the door, it’s heavy with the reinforcing framework and I opted to keep it propped open, when needed with a scrap 4″ x 4″ timber we had. I wouldn’t trust a locking type hinge with the weight of the door.
This morning, I filled the bottom four inches with composting manure which will release a small amount of heat while it breaks down. Then I put in a mix of excavated dirt, with bagged garden soil and more manure over that. Some of the dirt was frozen when I put it in but within an hour, the temperature inside the frame was markedly higher than outside and the soil had defrosted so I leveled things out and planted my radishes, spinach, romaine and mesclun lettuce. You can grow a lot of the brassicas during the winter and in the spring, the cold frame is a great way to acclimate your seedlings to the outdoors.
I did throw some mulch around the base to insulate it. I also read that I could place bricks, painted a flat black, inside and against the back wall to help keep the inside of the frame even more warm in the absolute dead of winter. The black bricks will warm up in the sun and then slowly release the warmth back into the frame during the night.
Again, this is a guide. One set of plans I saw included electrical wiring so you could put in a light bulb for heat or run heating elements under the soil to create a warm frame. You can vary the size based on materials you have on hand (we spent a bit more on materials so that we could create a cold frame based around the sliding door).
I can’t wait to have pics of my harvests with snow on the ground!
November 30th, 2010 at 1:36 am
That turned out fabulous and I know you will love having such a great cold frame at your disposal. I always overwinter young spinach under cover - and it leaps into growth as soon as the day length and sun strength starts increasing - giving me a huge jump on the early greens production.