Greenhouse glazing for short seasons
How glass, twin-wall polycarbonate, and film compare for heat retention, snow load, and light in cold regions.
Read the guide
Greenhouse & cold-frame gardening
Stretching the growing season where summers run short.
Across much of Canada the frost-free window is brief and unpredictable. These notes collect working methods for greenhouses, cold frames, and low tunnels that hold heat, shed snow, and buy gardeners extra weeks at both ends of the season.
Three structures, three jobs
Choosing the right shelter for the climate you have
Season extension is rarely about one big greenhouse. Most short-season gardens rely on a mix of structures, each suited to a different stage of the year.
Cold frames
Low, glazed boxes that sit directly on a bed. They harden off seedlings in spring and protect cold-tolerant greens well past the first frosts.
Polytunnels & low tunnels
Hooped plastic over beds or paths. Inexpensive to build, quick to ventilate, and effective for spreading planting dates across several weeks.
Greenhouses
Glazed standing structures that hold warmth into the evening. The glazing choice matters more than size in regions with heavy snow load.
Guides
Field notes and how-to references
Each guide is written for gardeners working with limited frost-free days, drawing on publicly available horticultural references.
Building and using cold frames
Sizing, siting, and venting a cold frame so it works as both a spring nursery and an autumn salad box.
Read the guide
A season-extension calendar for Canada
A month-by-month framework for sowing, protecting, and harvesting under cover from late winter through the first hard freeze.
Read the guideWhat separates a good cover from a frustrating one
Heat, ventilation, and snow are the recurring constraints
A structure that warms quickly on a sunny March afternoon can cook seedlings by noon if it cannot vent. The same structure has to shed wet spring snow without buckling. These guides return to the same practical levers.
- Thermal mass. Water barrels and masonry inside a structure smooth out the swing between day and night temperatures.
- Ventilation. Roof and side vents, or simply rolling up tunnel sides, prevent overheating and reduce condensation disease.
- Snow load. Roof pitch and glazing strength decide whether a structure survives a heavy, wet snowfall.
- Orientation. Facing the longest glazed side toward the low winter sun captures more usable light.
Contact
Questions about a structure or a planting date?
Send a note using the form and we will read it. This is an editorial reference site, so replies are not guaranteed, but reader questions help shape future updates.
- Email: editor@localandshore.org
- Phone: +1 (204) 555-0148
- Mail: Local And Shore Garden Notes, 218 Portage Avenue, Winnipeg, MB R3C 0B9, Canada