December 21 Journal: Growing Greens in An Unheated Greenhouse


We are extremely excited about the results so far of our experiment to grow greens in cold, unheated greenhouses. Step into our greenhouse on freezing winter day is like entering a temperate haven from the harsh outdoor environment. Even on a grey day, with outside temps of 32, the thermometer in the greenhouse registered 45 F. Hats and gloves come off. When the sun is out, temps inside the greenhouse climb into the high 60s and even 70s, and off come the coats as well!

 The past couple of weeks in December brought night temps to a low of 8 degrees F. These conditions are a true test of how greens will grow in our unheated greenhouse. The greenhouse beds, planted outdoors in September long before the greenhouse was even up, are now well tucked in under hoops and reemay cloth. This shelters not only from the cold, but also from wind, which is most destructive to plants. In an unheated greenhouse such as this one, each layer of covering gives us temps as though we are one zone south, so under the reemay, it’s like we’re in Georgia two zones south of here.

While it may also be cold in Georgia this time of year, the varieties we’ve planted here are cold-loving greens like super hearty winter lettuces, spinach, and mache, a gourmet green grown and eaten all winter long in France. The plants do indeed freeze at night underneath their covers. But as the sun warms the greenhouse, the plants almost miraculously revive to vibrant green life. On the shortest day of the year, December 21, there’s a very brief window to harvest — between about 10 a.m. and 2 p.m. , with sunset around 3:30 p.m. We can harvest only on days that the temperature inside the greenhouse climb above freezing.

The lettuce and spinach are now baby size, perfect for eating. Harvesting involves cutting the tender leaflets to make a nice salad mix. We leave the emerging tiny heart to continue growing. This way, once the days begin to get longer, the plants will slowly grow well into March, when it will be time to plant the next crop in the greenhouse.

If you’re lucky enough to find mache, also known as ‘Vit’, or corn salad, in the supermarket, it is usually very expensive. It’s a lovely, nutritious, nutty-tasting green that adds a new dimension to a salad, or it can be eaten on its own. The tender whole plant is harvested and left intact until food preparation for maximum freshness.

The lettuce really seems to thrive in this environment. The lettuce actually squeeks with freshness and vitality when I cut it!

Bill cuts individual spinach leafs, leaving the rest of the plant to continue growing.

Here is the final share of the season, just a few days before Christmas. Butternut squash, potatoes, fresh lettuce mix, two dozen eggs, and a special treat:

Delicious honey maple hickory-smoked salmon to serve our holiday guests.

Bill has also been preparing lots of smoked cheese which shareholders got in a previous share. These make great gifts from the farm.

 We’re looking forward to a short couple of months of “cave time” indoors, while we pore over seed catalogs, crunch our numbers and create our plans and marketing materials for next spring’s harvest. We also have a new baby to look forward to by the end of January.

Happy Holidays to all! May you be surrounded, as we are, by the love and warmth of family and friends.

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9 Comments

Filed under Greenhouse

9 responses to “December 21 Journal: Growing Greens in An Unheated Greenhouse

  1. Kristen Herrick

    Maggie! This is so awesome good for you guys! I am curious though, did you plant a variety of spinach that does keep growing for sure? The varieties we had were supposed to be cut as a plant because they don’t come again and I thought that was how all spinach is. Also, what is the deal with the cheese????

    • maggiemehaffey

      Kristen, I don’t mean to mislead. Very little growing takes place by December in the greenhouse. We got everything to harvestable size before the days got too short. After the early part of Dec., growth sloooows, and the greenhouse serves as kind of a refrigeration unit for the greens. However, I did notice there is some growth happening even then. Spinach is one of those hearty greens that thrives in cool. The goal is to protect from wind not water so cells don’t burst, and nudge the temps up enough to keep them alive. I’m not sure, but I imagine the nutritional value is higher too!

  2. Very interesting! I am trying to figure out how to grow lettuce in an unheated hoop house now. I figure if I start them indoors now and put them out there in February it might work. I would love to try what you have done this year as well. Thanks for the info 🙂

    • maggiemehaffey

      Hi Leslie, Yes, as long as you choose cold tolerant varieties: esp. spinach, and winter hearty lettuces, you should definitely try it starting from seed indoors. We are going to try direct seeding arugula, mache and more lettuce in the greenhouse starting February 1, when we get about 10 daylight hours…what plants need to grow. Will let you know how that works out.

  3. hi,
    did you ever try planting Boc choy or Tot soi (bad spelling) in the fall?
    i planted them with the rest of my greens in my unheated greenhouse in the fall. all doing well this spring but the 2 chinese greens bolted soon. they never produced the stir fry greens i hope to get from them as i did when i did a spring planting. although i ate the fresh leaves as they were bolting and they were quite nice but not like the huge stalks i wanted to stir fry with.
    i planted them in mid fall so i am surprised they bolted this early spring.
    any experience w/ this?

    • maggiemehaffey

      Hi Jim — We have not planted those in our greenhouse. Bok Choi and Tat Soi are definitely cool-weather crops and most likely it’s now too warm during the day in the greenhouse for them, so they’re bolting. It sounds like they’re behaving like the spinach we planted last fall, which started to bolt in mid-March, so we pulled it out. Incidentally, the Giant Winter spinach we had planted bolted less quickly than the regular variety we grew alongside it. We are getting ready to pull the greenhouse on to the next plot, as the carrots, lettuce and other greens planted there can now survive on their own under Reemay and hoops.

  4. Hi and how exciting to find you! Our John is endlessly looking for ways to extend his harvest times but we have the most terrible winds and storms here and he is afraid a plastic hoop house will be ripped apart. Do you have this problem at all?.. So looking froward to following what you are doing! We are just aiming for self sufficiency and sharing. c

    • maggiemehaffey

      Yes, the plastic hoops might be too flimsy for you. You can also use galvanized electrical conduit instead of the plastic. It’s sturdier. You have to bend it into hoops, but you can use a pipe bender to get them into shape. Or create some sort of form to bend the hoops around. We use sandbags to hold the cloth down. We’re giving out our last Late Season Share on Wednesday. We’ve had unusually warmer weather until now, and no snow as yet. Once that happens, we will take the hoops down and take a break for a month…whew!

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