These Concrete Block Cold Frames are used to extend the growing season in early spring and late fall. They are fast and easy to construct.
Our growing season in Wyoming is very short. Most people only put seedlings into the ground after Memorial Day which is the last Monday of May. The garden is mostly done by the end of October as it starts to get cold. The growing season is only about 5 months long. Sometimes you won’t even get 5 months as frost is possible in September. As such, greenhouses and cold frames are very good to have to extend the growing season.
Cold Frames On East Side of Barn
When we planned our barn and attached greenhouse, we knew the cold frames had to be a separate DIY project. There would have been gnashing of teeth to try to fit it in during the construction of the house and barn. That said, the delay gave us an opportunity to figure out the best location for them. Ideally, cold frames should be south facing. In our case, that is not possible the way the barn is positioned. The only other spot available to us was by the greenhouse wall facing east and we went with that.
Materials For The Cold Frames
By the time we got round to finding time to build the cold frames, it was already early October of last year. We figured that the fastest way to do it was to build the boxes by stacking concrete blocks along the wall. It would have been a piece of cake if the land there was level.
Spot With A Slope
Unfortunately, there is a slope in that spot in both directions which made it quite challenging to stack those concrete blocks. Still we managed to pile on more soil to make it work more or less. Time was not on our side as it was already turning cold. We did the best we could and got the job done.
Construction Of The Concrete Block Cold Frames
We used a total of forty six 4 x 8 x 16 inch concrete blocks to build those 5 cold frames glued together with construction adhesive. It wasn’t perfect but it worked. We found vinyl barn sash windows as a lid for the cold frames. Ro-Ri San made wooden frames for each box so that he can attach the windows to the frames. That was very challenging because the concrete blocks were porous and broke off easily. He managed somehow and got all the pieces of wood screwed onto the concrete blocks and the windows attached with door hinges.
We had a break in the weather and was able to paint just the exterior of the cold frames with latex exterior paint that provides a mildew and algae resistant coating. That made the cold frames looked a lot better. There are 2 hollow pockets in each concrete block and the inside walls of the cold frames are not painted.
Filling The Concrete Block Cold Frames With Soil
Before we constructed the cold frames, we did line the base with cardboard boxes and ½ inch wire mesh. As soon as the cold frames were ready, I filled each one with a mix of mulch, raised bed soil, perlite, peat moss, and compost up to the height of the first block.
Then, I watered it thoroughly to get it ready for planting. I sowed seeds directly into the cold frames as it was already mid October. The seeds germinated and grew about two inches tall but they froze when it got colder. Since the cold frames are above ground, they need better insulation for the plants to survive the winter.
Planting In Early Spring
As I had mentioned earlier, most people only plant outdoors at the end of May or early June here in Wyoming. I started seeds indoors in March and transplanted them into these cold frames in mid April. It was still cold and I had to cover them with frost cloth.
Plants Growing Well
I removed the frost cloth in early May, and by the third week of May, the plants looked almost ready to be harvested.
I had to leave the windows opened or propped up with bamboo stakes during the day as it got above 80⁰F/26⁰C.
Here is a peek inside the cold frames at the end of May. Shortly after this picture was taken, I started harvesting these vegetables, while others are just only starting to transplant seedlings into the ground. I only picked sufficient vegetables for the day and left the rest to continue growing. It was wonderful because we had fresh greens every day.
This is my favorite box in early June just before I started harvesting these juicy Tom Thumb lettuce. I continued harvesting from these cold frames right through mid July. It got too warm inside these cold frames in high summer and we needed to repair these boxes and so I concentrated on growing in the raised beds outdoors instead.
We were in a bit of a rush when we first constructed these boxes and did not do a good job of levelling the ground. Also, there was some settling of the ground over the months. It wasn’t pleasant but we had to rectify what we did not do right the first time. The soil had to be taken out and the concrete blocks dismantled…ughh!
Then, we had to place 2 x 4 lumber to make a frame for the entire row of boxes anchored down with 12 inch rebars. We filled the frame with soil and compacted it with a hand compactor. We had to reline the area with fresh cardboard, replaced the ½ inch wire mesh, reassembled the concrete blocks and windows, and put back the good soil. It was messy and frustrating but we are glad it is all fixed now. Hopefully, this time the soil underneath will not settle or wash away because of the slope.
Similar Tools Used in This Concrete Block Cold Frames Post
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Dewalt Atomic 20V MAX* Circular Saw, 4-1/2-Inch
Black & Decker Corded Drill, 5.5-Amp, 3/8-Inch
Makita XFD12Z 18V LXT Lithium-Ion Brushless Cordless 1/2″ Driver-Drill
Metal Roofing Screws: (250) 10 x 1″ Galvanized Hex Head Sheet Metal Roof Screw.
48′ x 100′ 1/2inch Hardware Cloth Galvanized Welded Cage Wire, 19 Gauge
Dewitt P3 Pro 5 Landscape 5 Ounce Weed Barrier, 3 x 250 Feet (2 pack)
Landscaping The Fenced In Area
While we were at it, we decided to lined the entire fenced in area with more cardboard and landscaping fabric. We topped this area with small river pebbles. It made the area look so neat and tidy minus all the weeds.
Second Try For Fall Planting In These Concrete Block Cold Frames
In September, I started some seeds in our new Stand-Alone Greenhouse and transplanted them into these cold frames in early October. They were doing well until the weather started turning cold and they were stunted. Unfortunately, we had a very cold spell at the end of October where the temperature dropped into the teens (Fahrenheit) and they froze. This confirms the fact that I cannot plant in these cold frames in the fall/autumn as temperature drops unless I insulate them. That will be a project for another time.