Cold Frames
Heat Retention in Cold Frames: What Actually Works
A look at the thermal physics behind glass versus polycarbonate lids, soil thermal mass, and how frame depth affects overnight temperatures.
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Northern Canada Gardening
Cold frames and low tunnels for short-season growing
Notes on heat retention, venting, and frost-hardy greens for northern gardens where the season ends before you expect it.
Articles
Recent topics
Three focused pieces on extending the northern growing season with simple, low-cost structures.
Venting
Venting Cold Frames on Sunny Days: Timing and Methods
Temperatures inside a closed cold frame can exceed 40°C on a bright March day while overnight frost still threatens. This covers how to manage the swing.
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Hardy Greens
Hardy Greens That Survive Late Frost in Northern Gardens
Kale, spinach, mâche, and a few less-common varieties that hold up when temperatures drop below freezing after transplanting.
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Key topics
What this site covers
Short-season gardening in Canada's northern regions involves specific constraints. These are the practical areas this site focuses on.
Cold-frame construction
Frame depth, glazing materials, orientation relative to slope and prevailing wind, and drainage — the decisions that determine whether a cold frame is useful or marginal.
Low tunnels and row covers
Wire hoops, PVC arches, and floating row cover for shorter-term frost protection. When they're appropriate and what their limitations are compared to a rigid cold frame.
Frost timing in northern zones
Canada's northern regions face last-frost dates well into May and first-frost dates in August or September. Understanding local frost patterns is more useful than generalized zone maps.
Soil preparation under cover
Soil inside a cold frame behaves differently from open-bed soil. Moisture retention, compaction from condensation, and the effect of mulch on heat storage all change.
Crop selection
Which greens, root vegetables, and alliums are realistic for short northern seasons, and which commonly listed "cold-hardy" crops struggle in practice above the 55th parallel.
Season extension limits
Cold frames extend the season by weeks, not months. This site tries to be honest about what a cold frame can and cannot accomplish in a zone with persistent late frost.
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British Columbia, Canada