Season extension techniques
Extend the growing season with cold frames, row cover, low tunnels, and thermal mass to protect crops from frost and capture heat.
11 min · advanced
You will learn
- Select season extension methods matched to crop hardiness
- Install and ventilate row cover and low tunnels
- Use cold frames to buffer temperature swings
Degrees of protection
Season extension ranges from a few degrees of frost protection with lightweight fabric to longer gains with insulated structures. Match protection level to crop hardiness and your climate. Hardy greens tolerate light frost; tender crops need more insulation. Over-protection on warm days causes heat stress, so ventilation is as important as coverage.
Row cover and low tunnels
University of Minnesota Extension describes floating row cover draped directly over crops or over wire hoops as a low tunnel. Lightweight cover traps a few degrees of warmth and can exclude insects. Secure edges against wind. Remove or ventilate on sunny days to prevent overheating.
Cold frames
A cold frame is a bottomless box with a transparent sloped lid that captures solar heat. Sited against a south-facing wall, it hardens off transplants and grows salad greens into late fall and early spring. Open the lid on warm days and close before afternoon heat escapes. A thermometer inside guides ventilation decisions.
Planning for your climate
University of Minnesota Extension season extension guides list structures appropriate for Minnesota conditions, adaptable to other northern climates. Record minimum temperatures inside structures to learn what each setup achieves in your microclimate. Combine row cover inside a polytunnel for marginal nights when extra protection is needed.