A cheap way to warm greenhouse soil

What I’ve learned about gardening in Kodiak, Alaska:

• Carrots and kale thrive in our flip-flop coastal climate.
• Tomatoes and cucumbers thumb their noses at you.

Still we try. Tomatoes though, having traveled a few thousand miles to my dinner plate, are fit to photograph; but not fit to eat.
Tomatoes, as the rest of the world knows, crave warmth. So much so that an ideal temperature for these fussy plants lies between 70 and 92 degrees F. Seed Savers Exchange calls it the goldilocks zone. Too cold, say in the trenches of  32 to 50 degrees F, and tomatoes exhibit “cold stress” tantrums: leave shrivel and turn yellow; stems lose posture, and roots stop sucking up water. Oh, you want fruit to set? Forget it below 50 degrees, which happens to be a common outside temp in my spring and summer garden.

So, off to the greenhouse I go, with tomato plants, every day; twice a day. My neighbors probably find my agenda for the day more entertaining than TV: Take tomatoes out in the morning [to the greenhouse]; bring tomatoes back [into the house] at night; carry tomatoes out; bring them back in. Lift. Carry. Repeat.
You might be thinking at this point, “Marion, why don’t you rig a heater up in the greenhouse?” Good idea, until you realize that in spite of six wind turbines and a hydro power plant (together they provide an impressive 95 percent renewable energy resource for our island community), electricity costs .14 per kWh.
During one of those ah-ha moments for which I’m always grateful, the answer popped into my brain: What about Christmas rope lights? They generate a little heat; and don’t require much electricity…
So that’s what I did. I found a couple strings of clear, non-LED Christmas light on Amazon (For impressive quantities and colors: Christmaslightsetc.com). Then I pressed them into the dirt. The next morning, when I carried the trays of tomatoes out to the greenhouse, I simply rested them on top of the lights. A quick check of the soil thermometer showed the soil was 10 to 15 degrees warmer next to the lights–just the right amount for the root zones.

The last word:
I recently called in to Jeff Lowenfel’s Garden Party radio show, on Anchorage, Alaska’s AM 700 KBYR. Jeff, by the way, has the longest running garden column in the United States.
Jeff has a quick wit and we enjoy bantering back and forth on the air. “What you been up to?” he asked.
I told him about using Christmas rope lights to warm the soil in the greenhouse; a blessing since spring took its sweet time in coming.
After a pregnant pause (not recommended on live radio, but he was the host) Jeff filled the audio gap just in time.
“You’ve heard about tomatoes and red plastic mulch?” (According to Gardener’s Supply, red plastic mulch is supposed to improve yield and flavor of tomatoes and increase harvest by 20 percent.)
“Well hey, why not try red Christmas lights?”