Dealing with frost damage

Kale with frost damage in our urban vegetable garden. Photo by Rebecca Cuttler.

Kale is a famously cold-tolerant crop. But when temperatures dip far enough below freezing, its big leathery leaves can suffer.

In the picture above, our rainbow lacinato is still alive, but it’s kind of… droopy. Last week’s cold clear snap, with night-time temperatures of around -5 celsius and chilly sunny days, has taken its toll. My skin is uncomfortably dry, and so are the leaves of our kale plants.

 In a matter of days, some of the leaves turned into kale chips on the plants. The lack of humidity and freeze-thaw cycle sucked the moisture right out of them. 

Preventing frost damage on leaf crops
I asked my farmer friends (some of whom live on the east coast and are used to dealing with real winters) for advice on preventing another bout of “freeze-dried” kale. Their ideas included: 

  • If you expect a hard freeze, wet the leaves of your winter greens first with a sprinkler — the layer of ice will actually protect them (I have yet to try this, but it sounds like a fun experiment)
  • Cover your crop with a clear plastic polytunnel to prevent further frost damage. And protect the roots by spreading a layer of mulch over the soil.
  • If the damage has already happened, harvest whatever you can, blanch and freeze it and use it like frozen spinach. Or, make a giant batch of kale chips for your coworkers — Hollyhock Garden to Table has my favourite recipe.
  • Plant a different variety next time, and place your crop in a different (hopefully warmer) bed. Next year, I think I’ll try a curly-leaf kale instead of lacinato.

Polytunnels are no-brainers in the winter veggie garden. But, although I’m religious about using them on all my other beds, I’ve been hesitant when it comes to kale. The towering plants just look unhappy squished under plastic. In past years, with typical dark, rainy and not too cold Vancouver weather, a layer of mulch has been all I’ve needed to protect my kale. But this year, it’s time for a cover.

On Sunday, I did a rescue mission. I cut all of the damaged leaves off our kale plants — three heavy (kitchen sized) garbage bags worth — leaving just the crowns intact. Then I poked several tomato supports into the bed to create an extra-tall structure for a clear plastic cover. Fingers crossed that it will do the trick. I’m not sure if I’ll be able to harvest more kale this winter, but I’m taking comfort in the fact that it’ll be the first thing to grow back in the spring.

Observing the effect of freezing temperatures in your garden
One of our most important duties as gardeners is to observe and record the effects of changing weather and climate on our growing space. The day after a heavy frost, I noticed the following:

  • Our small garden contains several microclimates. At noon, one side of the yard was sunny and relatively warm, while another area (shaded by a hedge) was completely covered in ice.
  • With temperatures of -5 celsius, the soil freezes solid.
  • The biggest, most developed plants in our garden suffered the worst frost damage. In addition to the kale, our beefy chard plants (mulched and under a polytunnel) turned into a slimy mess. I cut away everything except for the innermost leaves and will leave those chard plants alone to regenerate for spring.
  • Our smallest, most low-growing plants weren’t really bothered by frost. Even my experimental outdoor microgreens, which haven’t yet developed their adult leaves, are perfectly happy. Similarly, our parsley and mache were pretty much fine. Same with our carrots, beets and onions.

The one good thing about freezing temperatures
While frost can wreak havoc with leaf crops, take heart in the fact that it concentrates sugars in the roots of your parsnips, beets and carrots. Yum.

What’s growing this week:
As mentioned above, we harvested three very heavy garbage bags of slightly wilted kale, along with a fourth bag of chard and assorted greens. And I have some parsley left over from last week. Our fridge is completely full, and I’m pawning kale off on my friends and making kale chips for everyone. I would blanch and freeze it, but our freezer is completely stuffed with zucchini.

I just roasted up one of our pumpkins, and toasted the seeds for a healthy snack. We have several more waiting on our kitchen counter.

Despite this week’s extreme harvest, there are plenty of things waiting for us in the garden: parsley, mache, beets, carrots, parsnips and onions.


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