12TH IN AN ONGOING SERIES
NUTS & BOLTS & DREAMS: A beginner's guide to farming

Greenhouse 101: Winter Survival Guide
Once you know when to fold ‘em and when to hold ‘em, you, too, may say “let It snow!”

By Melanie & George DeVault

January 12, 2004: It was the heaviest snow of the season in Pennsylvania. Twenty-seven inches of the white stuff covered the ground last February as George crept down the one open lane of our two-lane state road in 4-wheel drive. He was responding to a fire call, but the farmer in him couldn’t help but notice on the way to the firehouse that a neighbor’s greenhouse had collapsed overnight. The middle of the 96-foot structure was smashed flat to the ground. The end walls of the structure slanted inward, warped at odd angles by tons of snow. Ouch!

It was any grower’s worst nightmare.

Heading home a few hours later, George looked at the neighbor’s trashed greenhouse from the opposite direction. What he saw sent another shiver down his spine. A second house lay in ruins.

“Are our four houses still standing?” he wondered.

They were, thankfully. We’ve learned to give Mother Nature a little sass (with a lot of elbow grease). Because while nothing is totally safe from the rages of Mother, be it heavy snow or howling wind, there are certain things you can do to help greenhouses—this includes high tunnels, hoophouses and coldframes—stand up to those rages.

In earlier columns, we’ve addressed what we grow under cover. Welcome to Greenhouse 101, where we share all of the little and not so little things we never imagined we’d have to deal with when we built our first greenhouse in 1995. Some lessons we learned the hard way. Fortunately the process hasn’t been that painful or expensive, for us at least (so far).

We first learned about wind when the 100- by 40-foot plastic skin from a friend’s hoophouse ended up in the treetops 200 yards away from the house’s steel skeleton. (OK, something close to that happened to us once, too. So smile smugly if it hasn’t happened to you—yet—and read on).

Lesson #1: If you live in a wind tunnel, attach greenhouse plastic as firmly as possible all around the structure. Batten down anything that will flap in the wind. And secure those roll-up sides, matey. Use ropes, bungee cords, cement blocks, long stakes, whatever it takes.

Lesson #2: Keeping a greenhouse covered year-round requires year-round management. If it’s a heated structure, you need to keep propane in the tank (or wood or coal in the firebox), whether you have crops in the ground or not, in order to fend off the snow and ice.

Dealing with Snow

We’re starting with snow, since it’s that time of year already. On December 7, 2003, the first snowstorm of the season gave us a whole foot of the white stuff. (We got off lucky; the rest of Northeast wasn’t so blessed.) That’s when we noticed our neighbor’s greenhouse frames that collapsed earlier this year were bare going into this winter. Ah, experience, the great teacher. The neighboring grower farms rented ground and simply lives too far away to deal with greenhouse upkeep when foul weather can make driving dicey.

Lesson #3: If you can’t be there to respond to changing weather conditions, don’t tempt fate; uncover the frame for the winter.

Lesson #4: Plastic is cheap, a whole lot cheaper than greenhouse frames in the grand scheme of things. Be sure to save the old plastic; it’s virtually indestructible. You can reuse it for any number of things, such as covering coldframes, new end walls, storing equipment, or adding an extra layer of protection for ground-planted crops in hoops (inside the greenhouse or outside). We even used old plastic as a ground cloth to keep the new plastic out of the mud when covering our largest greenhouse.

Lesson #5: Don’t buy trouble. The neighboring greenhouses that collapsed were poorly designed. Their shallow-peaked roofs just could not shed snow efficiently; that’s why they now stand uncovered and useless.

In contrast, heavy snow and ice slide fairly easily off of our three gothic-arch high tunnels and even off of our quonset-shaped hoophouse. Of course just to be on the safe side, we often find ourselves helping the process along with a long-handled snow brush, a broom, or by banging a gloved hand on the plastic skin from inside the hoophouse to start an avalanche. The snow slides down from the peak and piles up harmlessly along the sides. We’ve had that hoop up for eight years and replaced the plastic only twice: once because of old age and once because of wind damage; never because of snow.

In our two heated double-poly greenhouses, we also manipulate temperature and inflation to fight snow and ice. This has been a process of classic on-the-job training. Snow, sleet and slop started almost as soon as we covered our first house in March 1998. We sent a frantic email off to our friend and mentor Cass Peterson, who was running Flickerville Mountain Farm and Groundhog Ranch in Dott, Pa. (For the full story of the Groundhog Ranch, visit the bookstore for Truckpatch: A Farmer’s Odyssey, a collection of Ward Sinclair’s award-winning Washington Post columns about the joys and sorrows of producing organic food for body and soul at Flickerville.)

As usual, Cass promptly answered our prayers…with the following email: “When the overnight temperatures are mid to upper 20s and the snow is wet and minimal (less than six inches accumulated), better to leave the inflation on,” she wrote. “Otherwise the snow will settle into the little valleys you have created between the struts with the loose plastic and add even more weight to the house.

“The time to let out the inflation is when the snow is heavy (more than six inches) with temps at 25 degrees or less and especially with no wind.

“Here’s why: If ambient temps are 25 degrees or lower, chances are that the outside layer of your poly is right at freezing. Snow will stick at this temperature. Weight increases. If there’s no wind, none of the snow is likely to fly off. You need to “create” snowslides off your greenhouse by having the plastic temperature higher than 32 degrees. Thus, deflate and let the interior heat warm up the outside layer.

“If the ambient temps are above 25 degrees, chances are that your outside poly layer is above 32, and slides will occur better on the humpy slope of your inflated greenhouse.

“The real bugaboo is sleet/freezing rain,” she warned. “That’s when you jack up the temperature inside and collapse the inflation—to a point. If it’s a light sleet, the higher temp inside will soften it, and then, the next morning, you inflate to push the icy layer harmlessly (no slicing through plastic!) off the house.

“If it’s a hard sleet, you have to cycle between inflation and deflation. Yes, my man, even to the point of arising in the middle of the night. Down for a few hours at maximal heat, then up for an hour or two to slide off the softened slush. Then down again to build up heat, then up again.”

Thanks, Cass. Your sage advice, and that of other helpful growers around the country, helped get us through the past six seasons without any major disasters. (Never mind all of the minor greenhouse gaffes, although you, dear reader, will probably hear about most of them right here eventually.)

Lesson #6: Don’t be afraid to ask for help, whether in the form of long-distance advice or nearby helping hands from family, friends and neighbors.

We can’t stress the “helping hands” enough because this year we will be recovering all four greenhouses. The inside layer of plastic in Melanie’s seed-starting house is sun-rotted along the ridge, we just noticed. That means it is leaking both air and heat. The outside skin is probably not inflating quite as tightly as it could, so we’re also losing heat there. After six full years of use, though, we’ve gotten our money’s worth out of the plastic (it’s only rated for three years).

Plastic sheeting elsewhere around the farm is variously patched, discolored, stretched, stressed, torn and just plain worn out, kind of like the farmers at this time of year. But thinking of the job ahead as a modern-day barn raising—complete with a big brunch and a bunch of warm-hearted friends—already gives us something delightful to look forward to in the new year.

So, let it snow and blow. The propane tanks are nearly full. Brooms and snow brushes stand at the ready (a snow shovel, too, so we can dig our way into the houses). We’ll order and pay for the new plastic by early January—in order to take advantage of an eight percent discount from our local greenhouse supplier—and we’ll be all set to go when we’re pale, rested and ready.