Greenhouse Cold Frame

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If you want to leverage your vegetable garden a little longer , or get started a little bit earlier, you can easily set up a “cold frame” around it. A cold frame is simply a plastic sheet “house” that your garden lives inside of, which shields your plants from wind & cold (and snow if it’s sturdy enough).

What you need:

  • 1/2 inch CPVC pipes (beige plastic plumbing pipes at Lowes). Get 1 for every 2 ft (I used 9)
  • 1 Plastic sheet, the thicker the better (I used 10mil). Should be wide and long enough to drape over the whole frame and have extra.I used 10ft x 25ft
  • (Optional): another plastic sheet for reinforcing the bottom and extra shielding from wind.

Step 1: Build the frame

Grab the pipes, and bury the ends so that it forms an arc.Space them every 2 ft or so. Since they sometimes bend to the left or to the right, you can tie the top of the pipes together with a long string/rope so that they stay equally spaced. Tie the ends to a brick or a stone and place the brick 2 ft away from the end pipes so that the brick pulls on them and keeps them straight.

 

Step 2: Drape over with plastic sheet

No magic here.. just put the plastic sheet on top of the pipes, making sure that there is at least  4 inches extra on the sides (put bricks or rocks on top). The ends should have plenty  of extra so that the plastic can go all the way down and be secured with bricks as well.

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Step 3 (Optional): Extra steps for colder climates

I’m on a Zone 6 area, in November our lows hit 25 degrees and I thought that would be the end of the growing season but to my delight some plants were still fine (celery,special kind of  chard, thyme, oregano). In fact I think the rest of the plants might’ve made it if it hadn’t been for a couple of super windy days which blew the plastic sheet right off multiple times and exposed the plants to freezing temperatures overnight. In any case, several types still survived and so I came up with some strategies to help the plants survive.

Tip 1: Place extra plastic sheet all around the lower perimeter: I’m hoping this will help in the cases where the main plastic sheet comes a little lose at the bottom (because of wind or rain or the weight of snow). The extra plastic should help keep the elements out. Don’t make it too tall since it’ll block the sunlight.

Tip 2: Round up your dry leaves or grass clipping and put them all around the lower perimeter, forming a protective wall around your plants. This should help insulate from the cold, and with some luck the decomposition will provide some heat to the microclimate inside the cold frame as well. I’m not sure if the nitrogen of the grass will be a problem just yet..

coldframe-leaves

Tip 3: Bury kitchen leftover scraps (veggies, peels, NO MEAT PRODUCTS) in several spots inside. The decomposition should provide some heat to the microclimate inside the cold frame, and might keep the ground from freezing longer as well. I didn’t bury it deep at all, it just has a very thin layer of dirt on top (I’m not sure if it’ll invite a rodent problem yet, I’m experimenting with this for now). Another plus is that your soil will be fertilized for next year.

Is it worth it?

Yes, it’s totally worth it! I have a thermometer inside the cold frame, and even though the reading has hit below 32 on multiple occasions for several hours, plenty of plants are still fine. On a cloudy day, the temperature pretty much reflects the outside temperature (but remember the cold frame still protects from the wind). On a sunny day where it’s 32 degrees outside, I’ve seen the temperature get to 50. More importantly, I’ve observed in December that the ground was frozen outside the cold frame so much that I couldn’t get dirt for a pot, but the dirt inside the cold frame was not. Also, if the cold frame is up very early in the spring, the dirt will start warming up sooner so plants can be planted earlier.

So what didn’t make it during the winter (Zone 6)?
November: We’ve had a few days with lows in the mid 20s. Everything was fine until a couple of strong windy days with freezing temps which blew off the cover multiple times. The tomatoes and a special type of zucchini died miserably. Since those plants had been find until then, I suspect they would’ve held longer had the cover stayed put. The plants looked dried up so I harvested some gourds that look like a small Pumpkin at the end of November.
Oregano, thyme, celery, parsley, special type of chard (not meant for this climate) still going strong.

December: Oregano, thyme, celery, parsley, special type of chard still going strong. We’ve had high temps averaging low 40s, most lows mid 30s, some days freezing.

January, February: we’ll see 🙂

 

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