Unheated Winter Greenhouse Growing

Winter Greenhouse Gardening in Canada?

You betcha. At least that’s what I’m working towards. This is my second year with a greenhouse for the winter months, but as we moved in September and the greenhouse was full of weeds, this is really my first year aiming for more winter vegetables.

I’m experimenting with timing, growing the right varieties, and using an unheated greenhouse.

So how cold does it get here for our unheated winter greenhouse?

The coldest it gets here is -20C/-4F however it often goes above 0C/32F during the winter creating opportunities to harvest winter veggies. You always want to make sure you harvest veggies after they’ve thawed out otherwise they’ll end up mushy.

LOTS of snow with this Canadian greenhouse winter gardening

Our winter veggies go through freezing and thawing for a lot of the winter.

Winter veggies in an unheated winter greenhouse for winter gardening

After thawing winter vegetables will perk back up! See the snow in the background?

Winter vegetables in a winter garden

I’m also learning a lot by observation, some crops I’ve been leaving in the ground to see their cold tolerance threshold.

For example our baby bok choi was happy until the end of December when it reached -10C/14F.

Baby Bok Choi in the winter greenhouse

Best Winter Vegetables for a Greenhouse

Some crops can handle cold temps better than others. Remember some of your crops you’ll be able to harvest when they thaw out, or perhaps your winters don’t always get very cold until the January and February months. Every winter will be different year to year, we’ve had our coldest snaps in November and had rain instead of snow some years in Jan/Feb!

Winter veggies in a winter greenhouse

Great Winter Vegetables to Grow

  • Winter lettuce -Winter Density’ and ‘merveille des quatre saisons’
  • Mache
  • Spinach
  • Arugula
  • Green onions
  • Leeks – Giant Musselburg, Chinook, Bandit
  • Kale
  • Collards
  • Mustard Greens – Komatsuna, Senposai

Komatsuna winter harvest in the snow

  • Chinese Cabbage – Pai Tsai
  • Asian Greens- Tatsoi & Bok Choi
  • Carrots – Napoli
  • Parsnips
  • Turnips- Purple Top
  • Winter radishes- Black Spanish, Watermelon
  • Daikon radishes- Green Luobo, Sweet Meat, China Rose

All of these veggies need careful timing and this might take some practice!

Winter greenhouse

How to Time Your Winter Crops

When you grow a winter garden outside of a greenhouse you work on getting your timing right with hotter summer temperatures. Our greenhouse was full of peppers and tomatoes until September so I didn’t sow many crops until then. This coming season I plan on growing a cover crops to turn into the soil (soil building) to then sow winter veggies sooner.

I’m still working on getting varieties and timing right, but we had great success with a lot of the greens and many of them will overwinter for an early spring garden.

Winter density lettuce is a perfect winter vegetable to grow

Double protection with hoop tunnels inside a greenhouse

When we had our polytunnel greenhouse we often used a double tunnel for extra warmth for early spring soil warming and planting.

Double hoop tunnels- using low tunnels inside a greenhouse

Next winter I want to create some low tunnels inside the unheated greenhouse to have that double cold protection effect.

I first read about that in Eliot Colemans fantastic books on winter gardening.

Winter greenhouse gardening

Our winter greenhouse cover is a canvas.

I know many people also have plastic covers, which is what we want eventually because it increase the heat and sunlight. When we moved onto this acreage the greenhouse was already here. This is a 20’x 20′ greenhouse. You can see how we grow food year-round in a greenhouse and the state it was in when we moved with 10 foot weeds!

The roof is super solid though and the canvas cover does help with the snow loads

Winter greenhouse roof supports for snow load

Have you tried unheated winter greenhouse gardening? How was your experience?

Unheated greenhouse growing

7 thoughts on “Unheated Winter Greenhouse Growing”

  1. We have an unheated greenhouse. Spinach and slow bolt cilantro does the best. We did the low tunnels last year and they did well. This year there just wasn’t time. It is a snow storm today so added protection I put an old blanket on my plants. I keep my lettuces as you do… letting them freeze and thaw and they come back just fine. Thank you for your post!

  2. Your year-around gardening posts inspired me to build 3, 8×10 raised beds with hoop houses. Zone 8 and I’m thinking of direct sowing my tomatoes mid-February! I would love to see a post about how/when/what to start early for spring I’m an untested greenhouse. Love your stuff!

    • I personally find it easier to grow with raised beds in general. We use low tunnels over raised beds now as we have the greenhouse. We’re slowly adding raised beds into the greenhouse as we can afford it (1 out of 5 so far!)

  3. I live at 8500 feet in Colorado. I am trying to use passive heating methods only but my water barrels inside my greenhouse are freezing. Temps are ranging from 6-degrees F at night and usually 30s to 40s during the day. Do you have any suggestions? I might just give up until spring.

    • Most proper don’t realize that horse manure is free and creates steady heat. People love horses but they don’t know what to do about the sht. Gardeners don’t like it because of the seeds in it. But as a heat producer it works.


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