Cold frames, greenhouses, and techniques for year-round growing.
Why Extend the Season
| Benefit | Description |
|---|
| Earlier start | Plant weeks before last frost |
| Later harvest | Grow weeks after first frost |
| Year-round growing | Fresh food all year |
| Expand options | Grow warm-season crops in cool climates |
| Better quality | Protect from weather damage |
Understanding Frost and Cold
Frost Terminology
| Term | Temperature | Effect |
|---|
| Light frost | 29-32°F | Tender plants damaged |
| Hard frost | 25-28°F | Most plants damaged |
| Killing frost | Below 25°F | Season-ending |
Cold Tolerance
| Category | Examples | Tolerance |
|---|
| Tender | Tomatoes, peppers, basil | Killed by any frost |
| Semi-hardy | Lettuce, chard, celery | Light frost OK |
| Hardy | Kale, spinach, cabbage | Hard frost OK |
| Very hardy | Garlic, leeks, parsley | Can overwinter |
Simple Season Extension
Row Covers
| Type | Temperature Boost | Light Transmission |
|---|
| Lightweight | 2-4°F | 85-95% |
| Heavyweight | 4-8°F | 50-70% |
| Frost blankets | 6-10°F | 30-50% |
Uses:
- Frost protection
- Pest exclusion
- Wind protection
- Earlier planting
Mulch for Protection
| Method | Application |
|---|
| Heavy mulch | Cover cold-hardy crops for winter harvest |
| Straw bales | Windbreak, insulation |
| Leaf cover | Insulate root vegetables |
Water and Thermal Mass
| Technique | How It Works |
|---|
| Water-filled containers | Absorb heat by day, release at night |
| Wall-o-Water | Ring of water tubes around plants |
| Plastic jugs | Simple DIY thermal mass |
| Dark containers | Absorb more heat |
Microclimates
| Location | Temperature Effect |
|---|
| South-facing walls | Warmer, reflected heat |
| Under evergreens | Less frost |
| Low areas | Frost pockets (colder) |
| Near structures | Heat from building |
| Raised beds | Warmer, better drainage |
Cold Frames
What Is a Cold Frame
A low structure with a transparent top that traps solar heat.
| Component | Purpose |
|---|
| Frame | Insulated sides (wood, straw bales) |
| Top | Glass, polycarbonate, or plastic |
| Back | Higher than front (angled lid) |
| Orientation | Faces south |
Cold Frame Uses
| Use | Timing |
|---|
| Hardening off transplants | Before planting |
| Starting cool-season crops | Late winter |
| Extending fall harvest | Into winter |
| Overwintering | Cold-hardy crops |
| Early seed starting | Spring |
Building a Basic Cold Frame
| Dimension | Recommendation |
|---|
| Width | 3-4 feet (reach from one side) |
| Depth | 2-4 feet |
| Back height | 18-24 inches |
| Front height | 12-14 inches |
| Angle | 30-45 degrees toward sun |
Materials Options
| Frame Materials | Top Options |
|---|
| Lumber (2x12) | Old window |
| Straw bales | Polycarbonate sheet |
| Brick/concrete blocks | Greenhouse plastic |
| Recycled materials | Plexiglass |
Cold Frame Management
| Factor | Management |
|---|
| Ventilation | Open when above 45-50°F inside |
| Watering | Check weekly, don't overwater |
| Heat | Can add thermal mass or heat cable |
| Snow | Clear off or let insulate |
| Pests | Watch for rodents |
Low Tunnels
Structure
| Component | Description |
|---|
| Hoops | Wire, PVC, or conduit bent into arcs |
| Cover | Row cover, plastic, or shade cloth |
| Height | 2-4 feet |
| Width | Width of bed |
Low Tunnel Types
| Cover | Use |
|---|
| Plastic | Maximum heat, needs venting |
| Row cover | Frost protection, breathable |
| Shade cloth | Summer cooling |
Building Low Tunnels
| Step | Instructions |
|---|
| 1. Insert hoops | Every 4-5 feet along bed |
| 2. Secure bases | Push into ground or use stakes |
| 3. Drape cover | Over hoops |
| 4. Secure edges | Bury, weight, or clip |
| 5. Provide access | Open ends or clips for lifting |
Caterpillar/Quick Hoops
Simple, movable low tunnels:
- 10-foot EMT conduit bent into hoops
- Row cover over top
- Easy to move between beds
- Inexpensive and effective
High Tunnels/Hoop Houses
What They Are
Walk-in structures with plastic covering, no supplemental heat.
| Dimension | Typical Size |
|---|
| Width | 14-30 feet |
| Length | 48-96 feet |
| Height | 10-14 feet at peak |
Benefits
| Benefit | Details |
|---|
| Extended season | 4-6 weeks longer |
| Weather protection | Rain, wind, hail |
| Better quality | Less disease pressure |
| Earlier tomatoes | 2-4 weeks earlier harvest |
| Year-round greens | With proper management |
Considerations
| Factor | Details |
|---|
| Cost | $2-5 per square foot DIY |
| Permits | Check local regulations |
| Orientation | East-west or north-south |
| Ventilation | Roll-up sides, end vents |
| Irrigation | Essential (no rain inside) |
| Snow load | Consider your climate |
Greenhouses
Greenhouse Types
| Type | Features | Use |
|---|
| Cold greenhouse | No heat | Season extension |
| Cool greenhouse | 45-50°F minimum | Overwintering |
| Warm greenhouse | 55-60°F minimum | Tropical plants |
| Hot greenhouse | 65°F+ minimum | Tropical year-round |
Greenhouse Considerations
| Factor | Details |
|---|
| Location | Maximum sun, protected from wind |
| Foundation | Varies by type |
| Glazing | Glass, polycarbonate, plastic |
| Heating | Propane, electric, solar |
| Cooling | Vents, fans, shade cloth |
| Benches | Maximize growing space |
Greenhouse Management
| Factor | Management |
|---|
| Temperature | Monitor daily, vent/heat as needed |
| Humidity | Ventilate to prevent disease |
| Watering | More critical (no rain) |
| Pests | Can be worse (no natural predators) |
| Fertilizing | Regular feeding necessary |
DIY Options
| Type | Cost | Skill Level |
|---|
| Plastic-covered wood frame | Low | Moderate |
| PVC pipe structure | Low | Easy |
| Greenhouse kit | Moderate | Easy-Moderate |
| Attached to house | Moderate | Moderate |
| Recycled materials | Low | Creative |
Indoor Growing
Windowsill Growing
| Crops | Requirements |
|---|
| Herbs | South window, 4+ hours sun |
| Microgreens | Any window, short duration |
| Sprouts | No light needed |
| Lettuce | Bright window or lights |
Grow Lights
| Type | Pros | Cons |
|---|
| Fluorescent | Cheap, good for seedlings | Limited intensity |
| LED | Efficient, full spectrum | Higher initial cost |
| High-intensity (HPS, MH) | Professional results | Expensive, hot |
Light Requirements
| Plant Type | Hours of Light |
|---|
| Seedlings | 14-16 hours |
| Leafy greens | 12-14 hours |
| Fruiting plants | 14-18 hours |
| Herbs | 12-14 hours |
Indoor Growing Setup
| Component | Purpose |
|---|
| Lights | Replace sunlight |
| Timer | Consistent day length |
| Shelving | Maximize space |
| Trays | Catch water |
| Fan | Air circulation |
| Heat mat | Seed germination |
Winter Harvest Techniques
What to Grow for Winter
| Crop | Notes |
|---|
| Spinach | Very cold tolerant |
| Kale | Sweeter after frost |
| Mâche/corn salad | Extreme cold tolerant |
| Claytonia | Very cold tolerant |
| Asian greens | Many are cold tolerant |
| Carrots | Mulch heavily, harvest all winter |
| Leeks | Very hardy |
Planting for Winter Harvest
| Key Principle | Details |
|---|
| Plant in late summer/early fall | Plants must reach maturity before days shorten |
| Count back from first frost | Add 2-3 weeks (slower fall growth) |
| Protect established plants | Easier than growing through winter |
Succession of Protection
| Temperature | Protection Level |
|---|
| Above freezing | Light row cover |
| Light frost | Heavy row cover |
| Hard frost | Cold frame or low tunnel |
| Deep winter | Covered cold frame |
Season Extension Calendar
Spring (Before Last Frost)
| Weeks Before | Action |
|---|
| 8-10 weeks | Start seeds indoors |
| 6-8 weeks | Cold frame for cool-season crops |
| 4-6 weeks | Low tunnels for soil warming |
| 2-4 weeks | Transplant cold-hardy crops |
| 0 weeks | Remove protection after frost danger |
Fall (After First Frost)
| Weeks After | Action |
|---|
| Before frost | Cover tender crops |
| First frost | Harvest tender crops, protect hardy |
| 2-4 weeks | Cold frames for ongoing harvest |
| Hard frost | Heavy protection for remaining crops |
| Winter | Harvest from under protection |
Key Takeaways
- Start simple - Row covers provide significant protection cheaply
- Know your crops - Some handle cold better than others
- Ventilation matters - Cold frames and tunnels need venting
- Plant at the right time - Winter crops need to mature before days shorten
- Layer protection - Multiple layers as temperatures drop
- Monitor temperatures - A min/max thermometer is invaluable
- Build gradually - Start with row covers, progress to cold frames, then tunnels