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A Guide to Growing Cold Hardy Plants Under Cover - Unheated Greenhouse Growing

I remember the day I found out that it is possible to grow cold hardy vegetables before and after my first and last frost dates. I was blown away. Here I had always thought outdoor gardening had to be packed into just a few short months and low and behold, I was wrong!

It happens that I have a small 10' x 12' unheated greenhouse that works perfectly for growing early and late cold hardy veggies. The trick has been figuring out exactly how to do this, finding lists of cold hardy seeds, and trying to figure out seed dates.

Winter greenhouse in Canada used as a cold climate greenhouse to grow cold hardy plants.
My greenhouse in March, growing cold hardy vegetables under cover inside the beds.
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Unfortunately I have not got this information completely perfected for you. But I am so excited about what I have found out I don't want to wait any longer to share it so that YOU can get started growing cold hardy vegetables as well!

A lot of what I have learned has come from Eliot Coleman's book The Winter Harvest Handbook. I highly suggest purchasing this if you wish to learn more on growing cold hardy vegetables through the cool months of the year.

How to Grow Cold Hardy Vegetables

Plants protected from the elements can survive much colder temperatures than plants exposed. This is especially true of the wind. To grow cold hardy vegetables in winter months you will need at least two layers of cover, ideally having 3 layers.

The layers necessary for growing cold hardy vegetables are as follows:

  • A greenhouse. (This is not necessary, cold hardy vegetables can be grown using only the following 3 layers)

  • 6 mil Poly. Inside my greenhouse I just use two layers of 6 mil poly right next to each other. If building a poly tunnel for winter growing, it is important to build two hoops with a 4 to 6 inch layer between. This layer of air between the layers of poly acts as insulation.

  • Light row cover. This row cover should be placed 2 to 4 inches above the tops of the plants.

A poly tunnel in a cold climate greenhouse used for unheated greenhouse growing.