Insulation
Insulation Types for Sub-Zero Greenhouse Structures
A comparison of polycarbonate twin-wall, bubble wrap film, and rigid foam board options — including R-value trade-offs relevant to Ontario and Prairie winters.
Greenhouse Growing · Canada
Growing Leafy Crops Through a Canadian Winter
Practical reference for insulation, supplemental lighting, and humidity management in backyard and small commercial greenhouses operating below freezing.
Greenhouse interior during winter production. Photo: Wikimedia Commons / CC BY-SA
Topics
Three Factors That Determine Winter Yield
In Canadian climates with extended frost periods, leafy crop production in unheated or minimally heated structures depends on managing heat loss, light availability, and moisture levels together.
Lighting
Supplemental Lighting Hours for Leafy Crops in Winter
How day-length extension and photoperiod management with LED and HPS fixtures affects growth rate, bolting risk, and energy cost through December–February.
Humidity
Humidity Control for Leafy Crops in Closed Winter Structures
Managing condensation, fungal pressure, and transpiration rates when ventilation is restricted — passive and active approaches for small operations.
Context
Why Winter Growing in Canada Is Different
Greenhouse operations in Canada face conditions that differ substantially from temperate climates. In many parts of Ontario, British Columbia's interior, Alberta, and the Prairie provinces, outdoor temperatures can drop below −20°C for sustained periods. A structure designed for spring extension may lose more heat than it captures through solar gain when days are short and skies are frequently overcast.
Leafy crops — spinach, kale, arugula, lettuce varieties, and Asian greens — are among the more cold-tolerant options, but they still require night temperatures above freezing and sufficient daily light integrals (DLI) to maintain meaningful growth rates. Below roughly 6 mol/m²/day of photosynthetically active radiation, most lettuce varieties enter near-dormancy.
The three articles on this site address each major variable independently: the thermal envelope of the structure, the light environment, and the humidity regime. Each one affects the others — a tightly sealed, well-insulated structure will accumulate humidity faster, for instance — so reading them together gives a more complete picture of what a small-scale winter operation requires.
Reference
The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) publishes technical notes on protected horticulture relevant to cold-climate operations. Agriculture and Agri-Food Canada maintains research summaries accessible through their publications portal.
Geographic Variation Across Canada
Conditions vary significantly by region. A double-layer greenhouse in the Lower Mainland of British Columbia faces mild but low-light winters, while a similar structure in Saskatoon must handle far greater heating demands but potentially clearer skies and better solar angles in January. Zone 3 and Zone 4 operations in northern Ontario or Manitoba may require fully heated structures rather than passive cold-frames to keep crops alive.
This site focuses on the range of conditions typical for Zones 4–6, where some level of supplemental heat is usually required but the structure can rely on a combination of passive solar gain and insulation rather than continuous mechanical heating.
Send a Note
Questions about specific growing conditions or corrections to the material on this site are welcome.