Sovereignty Module: Extend the Season
Extend the Season
Complete Greenhouse Construction, Season Extension, and Protected Growing Guide
Complete Greenhouse Construction, Season Extension, and Protected Growing Guide
Greenhouses extend the growing season by months, enabling food production year-round in cold climates. This campaign covers design, construction, heating, and management.
Chapter 1: Season Extension Methods
| Method | Temperature Gain | Cost | Complexity | Season Extension |
|---|---|---|---|---|
| Row cover (floating) | +4-8°F | Very low | Very low | 2-4 weeks each end |
| Cold frame | +10-20°F | Low | Low | 4-8 weeks each end |
| Hoop house (unheated) | +10-15°F | Low-moderate | Low-moderate | 6-10 weeks each end |
| Greenhouse (unheated) | +15-25°F | Moderate-high | Moderate | 8-12 weeks each end |
| Greenhouse (heated) | Controlled (any) | High | High | Year-round growing |
| Underground greenhouse (walipini) | +20-30°F (stable) | Moderate | Moderate-high | Year-round (passive) |
Chapter 2: Greenhouse Design Principles
| Principle | Rule | Reason |
|---|---|---|
| Orientation | Long axis east-west | Maximum south-facing glazing for winter sun |
| Slope (roof) | Perpendicular to winter sun angle (latitude + 15°) | Maximum light transmission in winter |
| North wall | Insulated (not glazed) OR thermal mass | No useful winter light from north. Insulate or store heat. |
| Ventilation | 15-25% of floor area in vents (ridge + side) | Prevents overheating, controls humidity |
| Thermal mass | 2-5 gallons water per sq ft of glazing | Stores daytime heat, releases at night |
| Foundation | Insulated below frost line | Prevents ground heat loss |
| Size | Minimum 8×12 feet (practical minimum) | Smaller = harder to regulate temperature |
| Height | 8+ feet at ridge | Hot air rises — tall = cooler at plant level |
Chapter 3: Glazing Materials
| Material | Light Transmission | R-Value | Lifespan | Cost | Best For |
|---|---|---|---|---|---|
| Single glass | 90% | R-0.9 | 50+ years | High | Permanent greenhouse (cold climates need double) |
| Double glass (insulated) | 80% | R-2.0 | 50+ years | Very high | Cold climates, heated greenhouses |
| Polycarbonate (twin-wall) | 80% | R-1.5 to R-2.5 | 15-20 years | Moderate | Best all-around (light, strong, insulating) |
| Polyethylene film (6 mil) | 85-90% | R-0.8 (single) / R-1.5 (double) | 1-4 years | Very low | Hoop houses, temporary structures |
| Fiberglass (corrugated) | 75-85% | R-0.8 | 10-15 years | Low-moderate | Durable, hail-resistant |
Chapter 4: Heating Systems
| Method | Fuel | Cost to Run | Complexity | Best For |
|---|---|---|---|---|
| Thermal mass (water barrels) | Free (solar) | None | Very low | Mild climates, buffer only |
| Compost heating (hot bed) | Organic waste | None | Low-moderate | Spring start, propagation |
| Rocket mass heater | Wood (small amount) | Very low | Moderate-high | Cold climates, off-grid |
| Wood stove | Wood | Low | Low | Cold climates, available wood |
| Propane/natural gas heater | Gas | Moderate-high | Low | Reliable backup, commercial |
| Electric heater | Electricity | High | Very low | Small greenhouses, backup |
| Underground air tubes (GAHT) | Free (earth heat) | None (fan electricity) | Moderate | Year-round passive heating/cooling |
Compost hot bed: Fill raised bed with 18-24 inches of fresh horse manure + straw. Top with 6 inches of soil. Decomposition generates 120-160°F for 4-6 weeks. Plant directly in soil above. Provides bottom heat for early starts.
Chapter 5: Walipini (Underground Greenhouse)
| Step | Action | Specification | Details |
|---|---|---|---|
| 1 | Excavate pit (6-8 feet deep) | Length east-west, width 10-20 feet | Below frost line = stable 50-55°F year-round |
| 2 | North wall: vertical, insulated or thermal mass | Full height (6-8 feet) | Reflects light, stores heat |
| 3 | South wall: shorter (3-4 feet above grade) | Angled glazing facing south | Maximum winter sun penetration |
| 4 | Roof: glazed (south slope only) | Polycarbonate or polyethylene | Angle = latitude + 15° for winter optimization |
| 5 | Drainage: French drain around perimeter + sump | Gravel + perforated pipe | Underground = water table risk. Drainage critical. |
| 6 | Ventilation: ridge vent + underground air tubes | Passive or fan-assisted | Prevents overheating in summer |
| 7 | Stairs/ramp entry | On east or west end | Access without losing heat |
Advantages: Earth-sheltered = stable temperature (50-55°F year-round without heating). Only needs to add 10-20°F for tropical plants. Minimal fuel. Works in extreme cold climates (-40°F outside, still growing inside).
Chapter 6: Greenhouse Management
| Task | Frequency | Purpose | Method |
|---|---|---|---|
| Ventilation | Daily (open when >80°F inside) | Prevent overheating, control humidity | Open ridge vents + side vents |
| Watering | Daily-every other day | Plant hydration | Morning watering (allows drying before night) |
| Temperature monitoring | Continuous (min/max thermometer) | Track conditions | Record daily highs and lows |
| Pest monitoring | Weekly | Early detection | Inspect undersides of leaves, sticky traps |
| Soil fertility | Monthly | Maintain nutrition | Compost tea, organic fertilizers |
| Glazing cleaning | Seasonally | Maximum light transmission | Wash inside and outside |
| Thermal mass management | Daily (passive) | Heat storage/release | Uncover water barrels during day, cover at night |
Reference Card
- Orient long axis east-west. Maximum south-facing glazing. Insulate north wall.
- Ventilation: 15-25% of floor area. Ridge vent (hot air out) + side vents (cool air in). Prevents overheating.
- Thermal mass: 2-5 gallons water per sq ft glazing. Black barrels on north wall. Free nighttime heat.
- Twin-wall polycarbonate: best all-around glazing. R-1.5 to R-2.5, 80% light, 15-20 year life, lightweight.
- Walipini: dig 6-8 feet deep, glaze south slope only. Earth provides 50-55°F baseline year-round.
- Compost hot bed: 18 inches fresh horse manure + straw under 6 inches soil. 120-160°F for 4-6 weeks.
- Winter growing (unheated): lettuce, spinach, kale, chard, Asian greens, carrots survive to 20°F with protection.
- Overheating kills more greenhouse plants than cold. Ventilate aggressively above 80°F.
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