Winter gardening without heated greenhouses
Think you can’t enjoy your winter garden without a heated greenhouse? Think again.
As long as you add layers to keep your crops balmy, you’ll be able to grow food all winter long!
Below is an excerpt Winter Harvest Manual By Eliot Coleman. It has been adapted for exploit on the Internet.
Winter gardening without a greenhouse
As we develop, develop and improve our winter harvesting practices, we have amassed a body of technical research on hardy crops and the impact of freezing temperatures. Copies of scientific articles on all aspects of greenhouse farming fill our cabinets.
Resistant crops
In the natural world, hardy plants like spinach and Swiss chard inhabit niches where frigid resistance is a requirement for survival. Annuals such as mâche and claytonia have found their place to grow, germinating in autumn, growing in winter and sowing seeds in spring.
While the winter climate outside here in Zone 5 in Maine is too harsh for even the hardiest of these crops, the doubly temperate climate beneath the inner veneer of our frigid rooms provides them with conditions within the range for which they are adapted.
Unheated, uninsulated, unreliable!
Even after many years of working with this unheated system, I am still amazed by the daily miracle. The same three words come to mind every winter day – unheated, uninsulated, unbelievable!
When you come under the protection of one of our frigid greenhouses, you may want to take off your parka, as the microclimate you’ll encounter corresponds to a location about one and a half USDA zones south.
Once you get your hand under the row covers, you’ve moved another zone and a half south, where Maine winter definitely isn’t here. Outside, the climate is Zone 5; the inner layer has a zone 8 climate.
Using a frigid house for winter gardening
We started using the phrase frigid house to describe these structures because the word unheated made it seem like we weren’t doing something – heating – that we should be doing.
Furthermore, it may be clearer to exploit the descriptive phrase high tunnel or frigid tunnel and avoid the word greenhouse altogether, since many people assume that unheated greenhouses are exorbitant, super-insulated technological marvels or elaborate heat storage devices. Neither does ours.
Embracing winter forces
The best brief statement to describe our approach is Buckminster Fuller’s epigraph to this chapter from his book Shelter (1932) —“Don’t fight the forces; exploit them.”
Instead of mourning the forces of winter and trying to fight them, we constrained our intervention to the climate protection provided by two translucent layers.
Instead of the usual thinking that sees greenhouses only as a way to grow heat-loving crops in frigid weather, we said, “So it’s frigid. Great! What vegetables grow well in the frigid?” The answer is about thirty hardy vegetables.
Combat power requires energy, and energy costs money. Our frigid storage approach takes everything our two translucent protective layers can get free from the sun, as well as the residual heat of the ground mass, and then works within those limits.
The same applies in reverse in summer. When the protected microclimate inside homes becomes balmy, we do not combat that heat with motorized greenhouse cooling systems. We exploit it to grow thermophilic plants.
Outer covering
When we first started growing crops in frigid storage, we covered all the houses with just one layer of plastic. We made this choice to maximize the amount of lightweight. Using two layers of plastic and blowing air into the space between them to inflate the plastic provides greater protection from the frigid, but also reduces lightweight by an additional 10 percent.
We also prefer to work with systems that are inexpensive and uncomplicated. Therefore, we decided to waive the cost of the second layer and the electric blower needed to inflate the layers.
Plastic greenhouse covers
We are interested in comparing greenhouse materials from different manufacturers to find the type of cover that lets in the most lightweight and retains the most heat. In our frigid climate, we want to raise heat gain and lightweight levels during the day, so we prefer covers that maximize these inputs.
Plastic covers are available with an anti-drip coating that causes condensed moisture to form a lean layer instead of droplets. Roofs with this type of coating not only allow more lightweight to pass through, but the lean layer of moisture also reflects heat waves radiating from the soil at night, thus helping to keep the air in your home warmer.
Growers in southern states where the frigid is not as intense may want to exploit plastics designed to block infrared input and thus prevent the greenhouse from overheating.
Using double covers
For experimental purposes, we tested one compact air-inflated house (17 by 36 feet) without heating. From the data we kept, low night temperatures in an air-inflated house were on average 2.2°C higher than in a cooled house with a single-layer exterior.
For example, on a frigid night when the outside temperature was -22˚ C, the temperature dropped to -17˚ C in a single-layer house and to 20˚ F (-7˚ C) under the interior row cover. For comparison, in the inflatable house the low temperature under the inner row cover was between 7˚ F (–14˚ C) and 24˚ F (–4° C).
Double cover observations
Our crop observations during this study revealed some captivating comparisons between both houses. Although we could not detect any apparent difference in the quality of harvestable-size crops, we did observe faster growth of fresh seedlings in the inflatable house during winter.
This house also warmed up faster on frigid mornings because the layer of sunlight-blocking frost that forms on the inside of the plastic melts more slowly in a single-layer house.
Based on this trial, we began double covering the frigid rooms where we would sow the fresh crops from December 15 to February 15. For other frigid rooms, like the one that protects the leeks from harvesting in mid-winter, we still advocate simplicity and better lightweight, and only exploit one sheet of plastic to cover the house.
Inner layer
The success of our work with frigid frames and then row covers convinced us of the advantages of the inner and outer layer concept. We wondered if we could do even more.
We considered placing smaller tunnel greenhouses inside larger ones, as some Japanese farmers did, but after further consideration we decided that the management and ventilation seemed complicated and the exploit of space unskilled.
Using uncomplicated systems
We considered motorized night shade systems made of reflective material, which are sometimes used in heated greenhouses, but were very exorbitant.
After reading all of the above we returned, as usual, to the simplest and cheapest option – a floating row cover as the inner layer.
If we started our winter business with more complicated systems, we would never know if they were really necessary.
Layering Considerations
Although we were concerned that floating row covers might be much less protective against the frigid than glass cooling frames, the self-ventilating nature of the row covers and their availability in immense sizes were overwhelming advantages.
And further, we didn’t know if we had already pushed our crops to the lowest temperatures that would be tolerated in the protected microclimate.
Our opinion, after many years of practical experience with winter harvesting systems, is that the protected microclimate we have created is effective primarily because it protects against wind (think of wind chill readings and the drying effect of frigid, parched winds on winter vegetation) and secondly because it protects against the variable moist, parched and snowy conditions found outside in winter.
In this microclimate, a few degrees of temperature does not seem to be a key factor in the survival of most of our crops.
Uncomplicated operation
We plan to place row covers over the crops just before it gets frigid enough to freeze in the greenhouse. One of the advantages of using row covers in a greenhouse is ease of management. Since there is no wind, there is no need to bury or weigh down the edges.
Even immense pieces can be easily removed and replaced for harvesting or other purposes without fear of being blown away by a gust of wind.
Covers for immense houses
For immense homes, our indoor covers are 20 feet wide and 50 feet long, which is immense enough to cover one quarter of a 30-by-96-foot greenhouse. The 48-foot long houses are covered by two pieces, each 15 feet wide. The covers are supported 12 inches above the ground by flat-topped wire gates.
The wickets are made from straight lengths of No. 9 wire, 76 inches long. The flat top is 30 inches wide, the same width as the beds, and each leg is 23 inches long. Thanks to this, the installed gates do not block the passage between the beds.
Spacing from the fabric
Wickets are spaced every 4 feet along the length of the bed, providing enough frame to support the fabric covering the rows. Once the fabric is in place, we stretch it and attach it with clips to the end gates of the quarter.
This prevents the fabric from sagging under the weight of condensed moisture, which can be quite significant.
We noticed occasional frost damage where the fabric had fallen and frozen to the leaves below, but no damage occurred where the fabric was not touching the plants. The edges of the material fall over the edge of the gates and rest along the side of the greenhouse or on a path.