Learn: Vegetables Can Freeze!

2 Dec

A student holds swiss chard moments before it's planted. Photo credit: Corey Butler, Jr., northfield.patch.com

It is a common misconception in today’s culture that food can only be grown outdoors in the spring, summer, and fall. Once it gets below freezing, everything dies, right?

Wrong. Sure, by the time a good solid freeze rolls around, the tomatoes are slumped on the ground and the garden is filled with dried, dead leaves and vines that rattle in the wind. But inside an unheated high tunnel (which will be referred to as a “greenhouse” for brevity from now on), the season is just getting started when everything is freezing off.  And it’s that time of year.

Sure, the hot peppers are slime. Yes, the tomatoes will not be around until next July. But saying “Nothing can grow past the first hard freeze,” is like saying, “No one can possibly live in Minnesota, where people walk around without coats on as soon as it gets above 32 degrees in December.” Which, in case you didn’t know, is a blatant lie.

A student prepares the soil for some swiss chard transplants. Photo credit: Corey Butler, Jr., northfield.patch.com

There are actually whole families of plants who not only survive a freeze, but actually thrive in the sort of weather that makes most of us want to sit down with a big cup of tea. For instance, spinach, lettuce, and carrots actually become sweeter, more tender, and more flavorful in the winter weather. Why?

When things freeze, the starch in them converts to sugar. This is why you should never store your potatoes in your garage over the winter, and also why parsnips are best eaten after they’re frozen a few times.

Cold-hardy plants actually freeze solid, but it’s in their genes to be able to thaw out and grow some more. This makes them perfect for growing in our Northfield, MN winters, whose low for today is 8 F.

Things do grow more slowly in the winter, due to the decreased temperatures (you’d grow less if you had to thaw out before eating too) and decreased light levels. For instance, spinach planted on August 8th could be harvested September 15th. But spinach planted in the unheated greenhouse on December 12th could be harvested around April 4th. So why is growing in an unheated greenhouse (aka “cold house”) so great?

A student regards fresh brassica and chard transplants. Photo credit: Corey Butler, Jr., northfield.patch.com

Firstly, excellent flavor. Cold-hardy crops actually taste better if grown in, you guessed it, the cold.

Secondly, early harvest. The earliest, earliest you could plant spinach here in MN would be maybe the first week of April. Guess what? By that time you could be cutting it out of the greenhouse.

Thirdly, growing in a cold house through the winter provides local, delicious food in a season where not much else is available. For the market grower (or school project trying to support itself financially), having a niche like this is invaluable.

For further reading, check out Eliot Coleman’s The Winter Harvest.  Did this post help you out? Let us know in the comments below!


3 Responses to “Learn: Vegetables Can Freeze!”


  1. “Mache” Pit « the frippery factory - April 10, 2011

    […] dubious about the fact that plants can survive a freeze, I’d recommend that you check out this post from a local school’s unheated hoophouse team. It’s a pretty decent explanation, and […]

  2. How to pick seeds for winter production « Artech Greenhouse Project - January 6, 2011

    […] to be planted, it’s time for some research. You should check out other posts on veggies (here, here, and here), do a quick Google (or Yahoo, or Bing) search, or peruse Eliot Coleman’s The […]

  3. Vegetables can freeze, part 2: Asian greens « Artech Greenhouse Project - December 14, 2010

    […] when harvested young. And as you may have remembered from the last “veggies can freeze” post, greens grown during the winter are sweeter and tenderer than their summer-grown counterparts.  So […]

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