Cold Frames & Season Extension
Written by David Rodgers β Updated March 2026
Extend your growing season by four to six weeks in both spring and fall β with simple structures that cost almost nothing to build.
A cold frame is one of the most practical investments a vegetable gardener can make: a simple bottomless box with a transparent lid traps solar heat, raises soil temperature, and protects plants from frost β often enough to grow salad greens through winter in Zones 6 and warmer. Cold frames can be built from scrap lumber and an old storm window for under twenty dollars, or purchased as ready-made kits. Beyond cold frames, season extension encompasses row cover fabric, low tunnels made from wire hoops and floating row cover, and full hoop houses β each offering progressively more warmth and weather protection for progressively more investment.
What This Guide Covers
The most important principle of season extension is ventilation β a cold frame in direct March sun can overheat to seedling-killing temperatures within an hour if not propped open. Cold frames work best for cool-season crops: lettuce, spinach, arugula, kale, mache, radishes, and overwintered scallions. They are also the ideal tool for hardening off seedlings started indoors, gradually acclimating them to outdoor conditions over seven to ten days before final transplanting. The full guide covers cold frame construction options and sizing, siting for maximum solar gain, crop selection by protection level needed, hoop house basics for larger plantings, and how to time plantings for each structure type across different zones.
A comprehensive, in-depth guide covering cold frame construction and siting, row cover types and uses, hoop house basics, crop selection for season extension, and hardening-off schedules by zone is currently in development. Subscribe to the Planting Atlas newsletter to be notified when the full guide publishes.
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About the Author
David Rodgers is the Founder & Head Gardener of Planting Atlas. With over 40 years of hands-on gardening experience in Oklahoma's Zone 7 climate, he researches, writes, and personally tests every guide on the site.
David draws from real backyard trials, soil testing, and trusted sources like Oklahoma State University Extension and USDA data to deliver practical, zone-specific advice that actually works.
Read more about David and Planting Atlas β