Row covers, tunnels, and progressive shelter levels
Row covers (lightweight fabric) lay directly over plants, trapping heat and protecting from wind and pests while allowing water and light through. They raise soil temperature 2-3 degrees and extend spring and fall seasons by 2-4 weeks each.
Low tunnels (6-foot-high plastic-covered frames) create mini-greenhouses. Cold frames (glass-topped boxes) work similarly but are stationary. Low tunnels cost less than greenhouses but require manual ventilation on warm days. They extend season by 4-8 weeks at each end.
Greenhouse and heated infrastructure
Unheated greenhouses (glass or rigid plastic walls) raise temperature 10-15 degrees above outside air by trapping solar heat. They allow year-round production of cool-season crops in temperate climates. Heated greenhouses add heaters and ventilation, enabling tropical fruit and vegetable production in cold regions.
Operating costs scale with heating and ventilation. Unheated structures use free solar energy but limit production to cooler-season demand. Heated greenhouses maintain steady production but depend on fuel costs and climate reliability.
Sequencing and crop timing
Farmers stage shelter types by crop need. Tender seedlings get row covers or cold frames. Established greens and roots use low tunnels or unheated greenhouses. Heat-loving crops like tomatoes and peppers move outdoors into open ground once frost risk passes.
Progressive shelter allows 2-3 growing cycles in protected space per year. Spring seedlings germinate in heated space, move to low tunnel for hardening, transplant to unheated greenhouse for final growth. Fall crops reverse the sequence, building cold tolerance before full exposure.