Four-Season Growing & Season Extension
In a temperate climate, the traditional growing season is 5-6 months. That leaves half the year eating only stored food. Season extension techniques can push fresh food production to 9-12 months, dramatically reducing pressure on preservation and storage systems.
Cold Frames
A cold frame is the simplest season extension tool: a bottomless box with a transparent lid. It traps solar heat and blocks wind, creating a microclimate 10-20°F warmer than outside air.
Building from Salvage Materials
Materials needed:
- Old windows, glass doors, or clear polycarbonate sheets for the lid
- Lumber, cinder blocks, straw bales, or earth walls for the frame
- Hinges (or just lay the lid on top)
Construction:
- Build a rectangular frame, back wall 18-24 inches tall, front wall 12-14 inches tall (creates slope for rain/snow runoff and sun angle)
- Face the glass south (Northern Hemisphere)
- Size to match your salvaged glass — a standard old window makes a perfect lid
- Seal gaps with straw, soil, or old rags — but leave the ability to prop open for ventilation
Critical rule: On sunny days above 40°F, you must vent cold frames. Interior temperatures can spike to 100°F+ and cook your plants. Prop the lid open 4-6 inches. Close before sunset to trap daytime heat.
Automated Venting (No Electricity)
A wax-cylinder vent opener (sold pre-collapse as “Univent” or similar) uses thermal expansion of wax to automatically open and close the lid. If unavailable, a simple prop stick and daily attention works.
What to Grow
Cold frames are not for growing tomatoes in December. They protect cold-hardy crops from the worst of winter:
- Greens: spinach, mâche (corn salad), claytonia, arugula, kale, lettuce (winter varieties)
- Roots: carrots (sown in fall, harvested all winter), radishes
- Alliums: scallions, garlic greens
Plant these crops in late summer/early fall (August-September). They grow to near-maturity before short days slow growth, then the cold frame keeps them alive for harvest through winter.
Low Tunnels and Row Covers
Construction
Low tunnels are hoops of bent material covered in fabric or plastic, creating a mini-greenhouse over a garden bed.
Hoop materials (in order of preference):
- Wire: 9-gauge or heavier, bent into arcs
- PVC pipe: 1/2 inch, flexible enough to bend (salvageable from plumbing)
- Willow or hazel rods: fresh-cut green wood bends easily, lasts 1-2 seasons
- Rebar with PVC: pound short rebar stakes, slip PVC over them for a sturdy arch
Covering materials:
- Greenhouse plastic (6 mil): best heat retention, lasts 1-4 years
- Row cover fabric (spunbond): breathes, lets rain through, less heat gain but no venting needed
- Double layer: plastic outside, fabric inside = best insulation
Dimensions: Hoops every 4 feet, 3-4 feet tall at peak, cover a standard 3-4 foot bed. Secure edges with sandbags, boards, or buried edges.
Temperature Gains
- Single layer row cover: +4-8°F
- Single layer plastic tunnel: +10-15°F
- Double layer (plastic + fabric): +15-25°F
- Cold frame: +15-25°F
- Cold frame INSIDE a low tunnel: +25-35°F (this combination can keep crops alive to -20°F outside)
Succession Planting
Succession planting means sowing the same crop multiple times at intervals, ensuring continuous harvest rather than a single glut.
The Basic Schedule
For a community of 50-100 people needing continuous salad greens:
- Sow lettuce every 2 weeks from early spring through late summer
- Each sowing produces for about 3-4 weeks before bolting or being harvested out
- By the time sowing #1 is finished, sowing #3 is ready
Sample Year-Round Schedule (Zone 6, Cold Frames + Tunnels)
| Month | Sow | Harvest | Notes |
|---|---|---|---|
| January | Nothing (too dark) | Cold frame greens from fall sowing | Harvest-only mode |
| February | Onion starts indoors, early spinach in cold frame | Winter greens | Days lengthening |
| March | Peas, lettuce, radish under cover | Overwintered spinach, scallions | Remove covers on warm days |
| April | Potatoes, beets, carrots, more greens | Spring greens picking up | Succession sow greens every 2 weeks |
| May | Beans, squash, corn after last frost | Radishes, lettuce, spinach | Start warm-season crops |
| June | Succession beans, more lettuce (shade it) | Peas, early potatoes, greens | Heat-sensitive crops may bolt |
| July | Fall brassicas (broccoli, cabbage), more beans | Beans, squash beginning, garlic | Start fall garden |
| August | Critical: sow winter greens, carrots, turnips | Tomatoes, corn, beans, cucumbers | Winter garden establishment window |
| September | Cold frame greens, garlic (for next year) | Fall harvest: potatoes, squash, roots | Begin preservation push |
| October | Cover crops on empty beds | Late greens, root crops, brassicas | Close cold frames at night |
| November | Nothing outdoors | Cold frame greens, stored crops | Transition to winter mode |
| December | Nothing | Cold frame harvest + storage | Shortest days, minimal growth |
August is the most important month for four-season growing. Miss the August sowing window and you will have no fresh greens from November through March.
Greenhouse Construction (Post-Collapse)
Design Priorities
Forget the hobby greenhouse. For community food production, build a high tunnel (also called a hoop house):
- Size: 20-30 feet wide, 50-100 feet long, 10-12 feet tall at peak
- Frame: bent metal conduit, cattle panels, or heavy wire hoops
- Cover: salvaged greenhouse plastic, or multiple layers of clear plastic sheeting
- Orientation: long axis east-west for maximum winter sun
- Endwalls: framed with lumber, doors at both ends for airflow
Thermal Mass Heating
No electricity means no heaters. Use thermal mass instead:
- Water barrels: Line the north wall with black-painted 55-gallon drums filled with water. They absorb daytime heat and release it at night. Each barrel holds ~460 BTU per degree F of temperature change.
- Stone/brick north wall: a masonry wall 8-12 inches thick on the north side absorbs and radiates heat
- Soil itself: raised beds inside the greenhouse store significant heat
- Compost heating: a fresh hot-compost pile inside the greenhouse generates 100-160°F heat for weeks. Run water pipes through the pile to create radiant floor heating.
A well-designed passive solar greenhouse with thermal mass can maintain above-freezing temperatures down to 0°F outside air temperature — no fuel required.
Winter Gardening: What Actually Works
Winter gardening in cold climates is not about growing — it is about harvesting. Plants grow very little when day length is under 10 hours. The strategy is:
- Plant in August-September when days are still long
- Crops grow to near-maturity before the solstice
- Cold protection (frames, tunnels) keeps them alive but dormant
- Harvest as needed through winter — the cold frame is a living refrigerator
The Hardiest Crops (Survive to 10°F/-12°C Unprotected)
- Kale (especially ‘Winterbor’, ‘Red Russian’)
- Spinach
- Mâche / corn salad
- Claytonia / miner’s lettuce
- Leeks
- Parsnips (sweeter after frost)
- Carrots (under heavy mulch)
- Brussels sprouts
- Collard greens
Indoor Sprouting
When nothing else grows, sprouts provide fresh nutrition in 3-7 days with no soil, no light, and minimal water:
- Mung beans, lentils, alfalfa, radish, broccoli seeds
- Soak overnight, drain, rinse twice daily
- Ready to eat in 3-7 days
- Extremely nutrient-dense: vitamin C, folate, enzymes
A community should maintain a continuous sprouting rotation through winter — 3-4 jars started on staggered days ensures daily fresh greens.
Integration with Community Calendar
Four-season growing intersects directly with the harvest labor calendar. Key labor peaks:
- Late July/August: most labor-intensive period — harvesting summer crops AND establishing winter garden simultaneously
- October: closing cold frames, final harvests, meat processing for winter
- March: opening cold frames, starting transplants, preparing beds for spring
Assign dedicated greenhouse/cold frame managers — these structures need daily attention (venting, watering, monitoring) that is easy to forget when other farm tasks are pressing.