Shall I Compare Thee To a Summer's Day?

Mrs. Havisham’s high tunnel

When I was in seventh grade, my very old school English teacher required us to memorize and recite Shakespeare’s 18th Sonnet, Shall I Compare Thee To a Summer’s Day. I’ve forgotten most of it (sorry Mrs. Warren!) but as I looked out the window on yet another cool and blustery day this weekend, leading into yet another terrifyingly frosty night, the lines “Rough winds do shake the darling buds of May” surfaced unbidden, and I reflected on how vivid those words are to me now.

We are no strangers to rough winds on this farm.

One year, over-eager to spread out a large sheet of landscaping fabric for early spring bed-prep, I took what was essentially a magic carpet ride, when one particularly robust gust lifted the fabric (and me atop it) and carried us both about twenty feet. I returned to Earth unharmed but ready to concede that task to a calmer day. Only now, after five winters at this farm, can I reliably fall asleep when the winter winds are rattling our windows.

So I’ve seen some long, cold winter nights, and some intensely blustery spring days, but when I looked at the forecast last week and saw two nights in a row of sub-freezing temperatures (followed, Monday and Tuesday, with decidedly chilly lows, albeit not definitive frosts), my heart sank. A late frost can spell disaster for a vegetable grower like me, as the tender summer crops like tomatoes, peppers, eggplants, basil, squash, and cucumbers all cannot survive even a short time below 32 degrees. I see it every fall—the next-day sun hitting the stiff, frost-dusted plants, which swiftly blacken, and wilt, and decay. I’m ready for that by the fall—sick of the bugs, sick of harvesting, just plain sick of squash.

But not now, in May! My plants were only just beginning their green little lives! I surveyed my high tunnel and counted—nearly half of the space was occupied by frost-tender plants: beans, basil, tomatoes, and squash. I thanked my lucky stars that I had not planted my eggplants, peppers, and cucumbers yet, though they were large enough to go out. They would have to wait in the heated greenhouse, that much was clear.

If I lost my beans, it would be no great thing—they had just begun to come up and I could replant. Same with my squash; I’d start harvesting later than I would like, but would not loose the season entirely. But my tomatoes? My grafted tomatoes were seeded back at the end of January, at a nursery in North Carolina. They needed weeks to grow big enough to graft, then time to heal from grafting, then further time to become large enough to go in the ground. Even if I reordered last week, I wouldn’t be able to expect a tomato any earlier than August, at best. That would not do at all.

Pause now and consider the miracle of weather forecasting. Weather systems are vast, complex, and unruly. Remember the idea of a butterfly flapping it’s wings in Brazil and rain falling over Beijing? That’s not much of an exaggeration. It is only with the advent of super-computing that scientists can run sufficiently detailed simulations to be able to tell us, with even moderate confidence, that there might be a bad frost six days from now. Until fairly recently, weather forecasters could not predict beyond 2-3 days out. Before that, the best you could do was to read the evening’s clouds as calling foul weather or fair to come. On Friday, a dreary, damp, but not particularly cold day, I could not help thinking that it did not feel like a frost was coming. It was not until the evening that the wind picked up, and our tiny polar vortex rolled in. Without the advanced notice of modern weather forecasting, there is no way that we would have been ready.

As it was, though, I had been strategizing all week. Most of our plants could be easily covered with reemay—a light and water transmitting fabric that provides a few crucial degrees of frost protection. We hooped the beds of squash, basil, and beans, draped them with reemay, tiny high tunnels within our larger tunnel. The tomatoes presented more of a challenge, however. Because I aim for an extra-long, highly productive tomato season, I plant my tomatoes early and they soon need supports to keep from flopping onto the ground. I clip the stems to strings, which hang down from overhead wires that run the length of the tunnel about ten feet off the ground. But those overhead wires and strings prevented me from simply hooping the tomatoes, and I worried that if I detached them and let them fall over they would start to grow poorly, and possibly get trompled. But I had a plan. We began by installing a line of wooden posts down either side of the bed, spaced every 4 feet. Next, we strung trellising twine in three levels along each side of the bed, forming a string fence to hold the tomatoes loosely up. Then we undid all of our trellising work, and ever so gently covered the whole enormous assembly with a particularly large sheet of extra heavy duty winter reemay. I tucked a high/low thermometer under the cover, down by the roots, curious to find out just how well my reemay would protect my plants. I also unearthed a remote temperature monitor that had fallen by the wayside the year before when a software glitch caused it to malfunction. After some rebooting and reloading I discovered that the extreme limit of its transmitting range was the corner of the tunnel nearest to the shop (where our router is located). A reading from that corner was likely to be unrepresentatively cold, but still a useful data point as I monitored my tunnel after dark.

The idea of reemay and similar products is simple. Floating row covers (as they are also called) act as a barrier for insects, but also help to hold the heat of the day, stored in the soil, in with the plants as the air temperature drops at night. While my high tunnel heats up quickly from sunlight, it is not particularly weather tight, and once the sun goes down it rapidly cools off. In a late frost situation such as we were anticipating, I could hope to score a couple degrees from the structure of the tunnel, but not much more than that. The addition of reemay would hopefully put us over the top, and keep everything from freezing even with a potential low of 29.

I had good reason to feel like our plants would pull through, but a nagging fear kept pushing at the back of my mind. Our farm usually runs a couple of degrees colder than the local forecast, and in this instance a couple of degrees could be the difference between tomatoes and blackened husks. Even beyond that, I knew that each night below 50 degrees was slowing down the tomatoes’ growth, and I worried that the cumulative stress of so many cold nights could negatively impact the whole season, even if the tomatoes pulled through these two bad nights.

I had a eureka moment.

Rentals Unlimited! Leafing through their catalogue I quickly found the heaters section and the equipment I had been hoping for: a portable, propane Salamander heater, capable of putting our ____ BTUs per hour. That ought to keep the tunnel 40 degrees even as everything outside froze. I was game.

Unfortunately, I was also stupid. With all other preparation completed, I took our minivan to Frederick and walked into Rentals Unlimited at about 4:15. I rented my equipment inside, then drove around back to pick up my 100 pound propane tank and the small heater. But as you perhaps already knew (and as I now will always remember) it is illegal (for good reason) to transport a 100 pound propane cylinder within an enclosed vehicle. Even if it weren’t illegal, it is very hard to fit one into a minivan and keep the cylinder upright. Several crazy schemes flashed to mind (van home, truck back? Andrew comes in the truck with all the kids?) before I realized that there was no way to accomplish my mission before Rentals Unlimited closed at 5. Cursing my lack of foresight, I drove home, heaterless.

As I mentioned, the wind picked up that night and the cold rolled in. From our kitchen, I could watch the temperature drop on the brand new weather station we recently installed in the yard. Wind gusts: 30 mph. Temperature falling: 40, 39, 37… I checked my remote monitor, which sent readings directly to my phone. The tunnel was cooling too, albeit two degrees behind the outside air. There was nothing left to do. I went to bed.

I checked my phone with trepidation the next morning. The sun was up, and it was above freezing in the tunnel. Then I scrolled back to see the low temperature history—31.6. But what did it look like under the covers? I had to go see. The green was still green. My plants had pulled through. But I was not ready to declare victory over the weather—Saturday night was supposed to be fractionally warmer than Friday, but windier too, and I know that forecasts still have a margin of error. Back to Rentals Unlimited I went (this time in the truck).

We set up the heater in the middle of the tunnel, careful to give all of the row covers a wide berth. I build up a platform out of cinder blocks and a metal sheet, to level the surface and avoid roasting whatever was growing beneath the heater. Then I tested it. Success! Heat poured forth, and the flames leapt up. And up…and I looked up and thought suddenly of the plastic covering my tunnel, and wondered what kind of heat it was rated to withstand. I held my hand several feet above the heater—hot, but not unbearable. Was the treatment worse that the disease? Belatedly, I decided to do some research.

During combustion sulfur in the fuel is combined with oxygen to form sulfur dioxide. Levels as low a ½ part per million (ppm) can cause injury on some plants. Once the sulfur dioxide enters the plant through the stomates, it reacts with water to produce sulfuric acid that will cause leaf burn, flecking and general chlorosis. Tomatoes and white petunias are very sensitive to this and will show signs in as little as one hour. They therefore make good indicator plants.

Was I about the burn down my whole tunnel or poison my tomatoes with the by products of propane combustion? Uneasy, I turned the heater off. That night, I set my alarm for 2 AM and 4 AM. When it rang, I checked my remote monitor, reasoning that as long as the temperature had not dropped below 31.6, my plants would pull through. If it did, I decided that I would turn on the heater for no more than 1 hour, and wait, in the cold outside. As a mentor of mine once said, you either stop worrying, or you stop farming.

It got cold Saturday day night. It killed the flowers Alice and Sylvan had planted; it burned my potatoes, uncovered in the field (Forgot about them! But they’ll be fine). But inside the tunnel, under reemay, it never sank below 34 degrees, and now, on Wednesday the strings are back, the fence is down, and we can all continue on with our lives.