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Easy Ways To Maximize The Harvest In Your Unheated Greenhouse

Easy Ways To Maximize The Harvest In Your Unheated Greenhouse [1]

Image source: Pixabay.com

Read part 1 in this series here [2].

For those of us living in northerly regions, using an unheated greenhouse in the winter may seem far-fetched. And yet, it’s perfectly feasible. Even way up north in hardiness zone 3, a simple greenhouse covered with flimsy plastic sheeting can give you a winter harvest. Greenhouse “glazing” (be it plastic sheeting, or polycarbonate or glass panels) can help replicate the climate 1.5 zones to your south; and further coverings inside the greenhouse (such as floating row covers) can give you the leeway of another 1.5 zones. In this way, a zone 3 winter becomes a zone 6 winter. While zone 6 isn’t exactly tropical, its climate supports the growth of cold-hardy vegetables.

The key here is “cold-hardy.” An unheated greenhouse won’t do for heat- and sun-loving plants like tomatoes, peppers or melons. But with a little thought, planning and experimentation, you should be able to harvest salad greens, leeks, hardy root vegetables, and cool-weather Chinese greens during the winter months.

Building the Best Greenhouse

The location of your greenhouse and how it’s constructed will have a huge impact on your harvests. Before you start building, consider the following:

How Cold is Too Cold?

Depending on your hardiness zone, you may be able to get by solely with passive solar and ambient heating. In colder regions, you may need to supplement some warmth. There are a number of ways that you can generate and/or trap heat without resorting to electricity or fuel.

Get The All-Natural Fertilizer That Doubles Garden Production! [4]

Especially if you are setting a foundation below the frost line anyway, a sunken greenhouse can provide the warmth plants — especially root vegetables — need. As the Cold Climate [3]Greenhouse Resource [3] explains, soil located 4 feet below the surface stays at a steady 40-50 degrees Fahrenheit regardless of air temperature.

Alternately, a trench or hole in the center [5] of your greenhouse, filled with manure, will generate heat as the manure breaks down; and as a bonus, you will always have fertilizer easily at hand! Another option is to create heat sinks by filling black 55-gallon drums with water [6]. The barrels absorb heat from the sun during the day and slowly release that heat at night. If you’re up for it, more complicated systems include solar heating and circulating water heated with solar power.

Regardless of how — or even if — you provide supplemental heat to your greenhouse, keep in mind that plants also need sunlight to thrive. During the shortest days of the year, growth will come to a standstill regardless of how warm your greenhouse is.

Choosing the Best Vegetable Varieties

As noted above, it’s essential to focus on cold-hardy vegetables for your unheated winter greenhouse. It may take some experimenting to find which varieties work best in your zone and your greenhouse’s microclimate, but to help you get started, consider these:

Timing Your Seedlings

It’s best to start your seeds in late summer or early fall so that your seedlings are well-established before extreme cold hits. However, you can sow throughout the winter. If you choose to plant during the coldest months, start your seeds indoors or use a heat mat for seed propagation. Tender seedlings are more sensitive to the cold and need a solid start before they’re left 24/7 in an unheated greenhouse.

Why Bother?

You’re not alone if you’re wondering whether digging a four-foot “basement” for a greenhouse and calculating the optimal roof slant is more work than it’s worth. But, if you’re reading this, it goes without saying that you already know the benefits of gardening, whether in winter or summer: the joy of dirt under your fingernails; putting tasty, nutrient-dense produce on your table; cost-savings compared to purchasing bland supermarket vegetables; and self-sufficiency. Using an unheated greenhouse in the winter brings extra benefits, including the cost-savings over a heated greenhouse, supporting the environment, and the joy of proving those folks wrong, who think it’s impossible to grow fresh vegetables in the depths of winter.

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