Winter Share Week 3; Staying Warm!

This week, as temperatures dipped into the teens, we’ve been making a push to increase the energy efficiency of our greenhouses. Technically called “high tunnels” or “hoop houses,” these structures are constructed of arched metal bows covered  in clear plastic film. Sunlight enters the house through the plastic and warms the soil and plants inside, creating a cozy micro-climate. The plastic creates a “greenhouse effect,” trapping some of the heat to keep the plants warm when the sun goes down. However, a single layer of plastic can only do so much in terms of heat retention. We find that our houses can provide a 5-10 degree temperature buffer, which certainly gives our crops a boost in the fall and spring “shoulder” growing seasons. But as we look towards increasing our winter growing and adding heat from our new wood-fired boiler, we’re going to need to increase that buffer significantly. There are 2 ways to improve heat retention: insulation and infiltration.

For the first, we are adding a second layer of clear plastic to our houses and installing an inflation fan that will create a 5″ bubble of air between the two layers of plastic. This layer of insulating air will add about 1.5 units of thermal resistance (R value) to our houses, while still allowing sunlight to shine through to the plants. Yesterday, after a low of 17 degrees, we had the opportunity to see the effect of this new insulation in real time. As the sun peeked over the horizon and warmed the greenhouses, the ones that had already gotten their second layer retained a layer of frost on top that was insulated from the heat inside, while the single layer houses almost immediately began to melt and drip; a sure sign that we were losing some of that precious heat from the inside.  Looking ahead, we will also be installing night curtains to further increase heat retention through insulation.
Meanwhile, we all know that even if your house is well insulated, you can feel cold if your windows are drafty! So we are also working on sealing up any gaps and cracks in the greenhouses to reduce air infiltration. We’ve installed simple but brilliant “corner wind panels” (additional pieces of clear plastic between the first and second bow) at each corner of each greenhouse to reduce air flow, and are hunting down and sealing up any other spots that cold air can sneak in. Gaskets on the doors, woodchips along the kick boards, and strapping to bridge the gap between plastic roof and wooden end wall are all coming into play here, too. With local veggies in high demand and relatively low supply during the winter months, we’re excited to increase our efficiency and up our game in the realm of cold weather growing. I hope you’re staying warm out there, too!
Cheers, Norah and the Sweetland Crew
Week 3 Winter Harvest
Acorn Squash, 1
Sweet Potatoes, 3 pounds
Celeriac, 2
Hakurei Turnips, 1.5 pounds
Napa Cabbage, 1 head
Kale, 1 bunch
Spicy Salad Greens, .25 pound
Garlic, 1 head

What’s Cooking This Week

You can find ingredients for all of these recipes in our farm store! We source meats, dairy, grains, beans, sweets, and more from local and sustainable producers. Don’t forget to use your CSA member discount!