After a mild November and December,
January is shaping up to be a fairly typical January here in Chicago.
Early this week, arctic air from the north drove the temperature down to 0 degrees Fahrenheit
or - 18 degrees Celsius.
This is the biggest test of our winter garden so far this year.
Today we'll take a look at how our crops are holding up,
but first I'll share temperature data that will demonstrate the benefits of growing under 2 layers of protection
in cold climates during the winter.
For 14 consecutive days, I recorded the maximum and minimum temperatures outside,
inside the hoop house,
and inside this cold frame.
Here in blue you see the maximum
and minimum outside temperatures recorded over the 2 week period.
The thick line on top reflects the maximum temperatures
and the thin line on the bottom charts the minimum temperatures.
The highest temperature outside was 41 degrees Fahrenheit
and the lowest was 0.
The last 3 days, in particular, were very cold.
When we add the maximum and minimum hoop house temperatures in green,
you can see it was consistently warmer in the hoop house.
The highest temperature recorded was 69.3 degrees Fahrenheit
and the lowest was 9.7.
The difference in maximum temperatures was most significant on sunny days
After a number of cloudy days, on the other hand,
you can see how the hoop house maximum temperatures
moved much closer to the outside temperatures.
So, clearly it was warmer in the hoop house than it was outside,
but did the cold frames inside the hoop house provide an additional benefit?
Let's take a closer look.
When we add the cold frame temperatures in red,
you can clearly see that the second layer of protection made a significant difference.
The cold frame maximum temperatures were consistently higher than hoop house temperatures,
except over a couple very overcast days
when they were about the same.
The difference was most significant on sunny days,
but would have been even greater if the cold frames weren’t
vented on some days to prevent overheating.
The minimum temperatures were higher in the cold frame than in the hoop house without exception.
And cold frame temperatures stayed above freezing except for the 3 coldest nights.
The lowest temperature in the cold frame was 20.9,
which is 20.9 degrees warmer than the outside low of 0 that day
and 11.2 degrees warmer than the hoop house minimum.
Now let's take a look at the average maximum and minimum temperatures
outside, inside the hoop house, and in a cold frame
to see if these temperatures are consistent with Eliot Coleman's observation
that each layer of protection effectively moves the garden 1 and 1/2 zones to the south.
The average outside high of 32 and low of 19.9
are typical for this time of year here in zone 5.
But the temperatures in the hoop house are closer to what you might see in zone 6b -
with an average high of 50.8 and low of 26.
Finally, the temperatures in the cold frame represent another move to the south.
An average high of 58.5 and low of 31.5
sound just about right for many zone 8 regions at this time of year.
So, clearly, 2 layers of protection offer a significant advantage,
but how did our plants hold up to 3 days with temperatures near 0 degrees Fahrenheit?
I’m happy to say almost all of our plants survived
and we continue to regularly harvest crops from our winter garden.
Some, like Georgia collards, Swiss Chard, and Perpetual Spinach
were clearly stressed by the cold, but are still alive.
Other crops seem to have been completely unfazed by the cold.
I’m particularly pleased with how well our tree collards are doing.
If we’re able to overwinter them,
we’ll have a new edible perennial in the garden.
Dinosaur kale, mustard greens, and tatsoi
are also doing fine.
And claytonia, which is very cold hardy, is thriving.
Unfortunately, we did lose some of our lettuce plants this week,
but I don't think it was because of the cold.
The morning after our 0 degree low,
cold frames were frozen shut and I wasn't able to vent them.
That day turned out to be very sunny,
and as a result the temperature inside the cold frame rose very quickly.
And I believe this is what killed some of our lettuce plants.
This is a great example of how having an automated venting system
can be very helpful.
I couldn't be happier with how our winter garden is doing.
Even after extreme cold and nearly daily harvests, there's still a lot growing.
I expect growth will slow down quite a bit over the next month or so,
but by late February it should start to pick up again.
And by early spring, the garden will be exploding with new growth.
Well, that's all for now. Thank you very much for watching,
and until next time remember you can change the world one yard at a time.