Store your Salads For Winter
by HC Burkholz
It was 3:30PM Tuesday, January 3rd. The afternoon sun shone brightly in the cloudless, cold winter sky. It would be another night of below zero temperatures here in Wisconsin. Last night it dropped to 10°F below zero. The high today was 0°F. We already have had three nights of 15°F below zero.
I decided to do chores a bit early this afternoon. That meant to gather the eggs our hardy and loyal hens had given on this cold day and secure the garden salad for the night. My winter salad garden has five varieties of lettuce as well as spinach, radishes and table onions. These were all seeded in October so they would be ready for use by the year's end. And they were all produced with energy that is free to most of us!
How's that?
Having been in the construction business and an avid gardener for most of my adult life, I have observed that the ground temperatures several feet beneath the surface are relatively stable all year long. This upper layer of the earth's surface, the crust, gets its constant temperature from the earth itself - from within. In this part of Wisconsin that temperature is between 48 and 55 degrees Fahrenheit. The sun's effect on the earth's surface is really not all that great. We find the soil temperature in the forested areas is relatively cool, even during the hottest summer days. In open areas of full sunshine, only the top foot or so is warmed to the 70° range in the summertime. When we reach the 4-5' depth in the earth's crust we find that the year around temperature may fluctuate as little as 5°F.
Past experience has taught me that
the season between December 1st and February 15th had two major factors required
for plant growth - heat and light - missing. Nights and usually days are very
cold and daylight hours are short. What effect do short days and cool
temperatures have on the "keeping" qualities of mature plants? Is it
possible to "store" lettuce simply by having mature plants enter a
kind of dormant stage? How long will they keep? How good will they be?
In an attempt to answer these and other questions I set out to use the two heat sources available to us. Solar heat during the daytime and ground heat to survive the dark night hours. I have already been greatly extending the growing season by using a SolarGardenDome enclosure during the early spring and fall. This enclosure provides a wind free environment. My growing season has averaged nine months for the past three years with the dome. By Thanksgiving the growing season using only solar heat was pretty well over. The dome protected the plants in temperatures as low as 20°, so I reasoned that in order to use the ground heat overnight I would need to provide more protection.
I built a rather large cold frame
within my SolarGardenDome. It was constructed with a 2x8 lumber box frame that
measured 10' x 14' in size and utilized a cover of 4mil sheet plastic available
from the local hardware store. I wanted my winter garden to be large enough to
provide an ample supply of salad greens during the coldest months. I figured
that a covering very close to the plants would be more effective than an
additional layer over the entire volume of air within the enclosure.
The garden did well until one night early in December when the temperature dropped to -4°F. The following morning I entered the dome with some apprehension, 4° below zero is 36° below freezing! Could the second cover close to the plants trap enough ground heat to prevent damage? As I stepped out of the wind into the frost covered dome the warmer air comforted me. I looked at the closed cold frame cover and saw frozen water droplets on the underside of the poly film cover. My spirits sank. With trepidation I lifted the cold frame cover. There was a light frost on the almost mature plants.
As I stood there looking at all that salad I suddenly felt a spark of hope. Lettuce, spinach, radishes and onions can all take a light frost. Maybe - just maybe they would be OK. The sun warmed the air in the dome and by early afternoon I was convinced that no damage was done. But it was a close call! I had to do more because Wisconsin gets much colder than a mere -4°.
Maybe an extra blanket? I drove a series of stakes in the ground within the cold frame and strung a sturdy line across them. This supported the carpet pad I draped over the plastic cover for the night.
The following morning the thermometer registered -15°F, 47° below freezing! I was anxious to get to the garden but didn't dare uncover it until the morning sun brought the temperature to at least the freezing point within the dome. I waited until 9AM to do my morning chores. After the chickens were fed and watered I walked to the garden and unzipped the frosted door. The entire dome looked like an igloo. As I stepped inside I noticed that the ground was now frozen hard. The blanket over the cold frame seemed a little reassuring - but 47° below the freezing point with no heat other than the earth's crust seemed like certain frost kill.
As I rolled the carpet pad back and saw droplets of water scurrying on the underside of the poly film I felt the thrill of victory over old man winter! I lifted the cover and shook the water off the plastic onto a lush crop of salad greens. Outside the dome the temperature was -7°F!
We had regular below zero nights for the next three weeks, at least three nights of -15°F. The soil temperatures within the covered cold frame remained stable, 40°F morning temperature climbed to 47°F by late afternoon. Outside the dome the daytime highs never climbed above 20°F.
The greens had for some time been
mature enough for picking and remained dormant and fresh. The Black Seeded
Simpson lettuce didn't show any new growth after cutting, while Oak Leaf and
Ruby Red lettuce produced crisp new leaves a couple of days after cutting.
Mature radishes were crisp and mild flavored. Bibb and Buttercrunch lettuce was
of good quality, as was the spinach. They all hung on in a state of suspension,
alive and keeping very well.
In the summertime when growth is fast I had been planting short rows and replanting regularly to maintain fresh, young salad greens. Now, in winter, to "store" salad greens I plant larger quantities in September and October that last through the dead of winter.
In past years I had started seeding salad greens in the SolarGardenDome by mid February. The days are long enough by then to allow the soil more time to absorb solar heat. Now, by using the cold frame or similar methods inside the dome I can extend the season virtually indefinitely!
