It's cold on Tiger Mountain. Not USDA hardiness zone cold. Oh, no. The USDA says I'm Zone 8, which is also the zone for much of Alabama, Georgia, Louisiana, Missisippi. Riiiight. I beg to differ on the zone itself, because I get single-digit (Fahrenheit) lows every winter, sometimes for weeks at a time. So, lets say I'm zone 7. That's still the hardiness zone for parts of the above-mentioned Southern states, central California, parts of Arizona. Think hot, muggy nights, hotter muggier days. Not my always-sleep-with-a-blanket-and-never-wish-for-air-conditioning climate.
No, it's not the winter cold we are dealing with here, it's the spring, summer, and fall cold. We're past the last freeze date but overnight lows are consistently in the low 40's and will remain below 50 well into July, when they will occasionally inch up into the low 50's, until August, when it cools off again. Daytime highs can be all over the place, from the 60's to the 90's, but the nights stay cold, even in the greenhouse, which provides plenty of daytime heat, but loses it rather quickly when the sun goes down. Not good for most solanums--eggplant, peppers, tomatoes--which refuse to set fruit at temps below 50 degrees.
So, I broke down and purchased heating cables for the greenhouse planting beds. My conscience and I struggled with the contradiction of using artificial heat to grow food when one of the reasons for growing my own food is to reduce our energy consumption. I've finally rationalized (wonderful thing, rationalization) that the increased harvests will more than offset the energy consumption from the heating cables. The cables are thermostatically controlled to shut off at 71 degrees, so they should be working only at night.
A week ago I buried a heat cable and a soaker hose in one of the planting beds, and planted out some sacrificial tomato plants.
The plants were so leggy from living in pots on the windowsill that I had to lay them in trenches, with the roots of each one practically touching its neighbor.
To trap the heat, I draped the bed with grow-therm:
I ran the lead to a min-max thermometer to the center of the bed, crossed my fingers and hoped for the best.
I'm delighted to report that, even with nighttime temperature in the rest of the greenhouse being in the mid-low 40s every night, under the tent it's been consistently 10 degrees warmer, right into the magic numbers needed for my heat-loving plants. The tomatoes are thriving. I've never known them to grow this fast. I can hardly wait to dig over the other bed and plant out my peppers, eggplant, and melons, all of which produce meager crops last summer, just as soon as the lettuce that's growing there begins to bolt.
And I can't help wondering--do you suppose I could grow okra?