Season extension
Keep crops thriving when temperatures tumble
Winter production rewards growers who balance insulation, targeted heat, and disciplined airflow. Use this guide to layer those systems, select resilient crops, and build a repeatable cold-season routine.
Set a winter mission statement
Decide whether you want consistent greens, experimental fruiting crops, or a frost buffer for nursery stock. Your equipment choices should match that mission. Document targets for minimum temperatures, humidity, and light hours so everyone on your team understands the threshold for taking action.
- Define the coldest outdoor temperature you expect and design equipment that handles ten degrees colder.
- Use our heating cost calculator to estimate fuel budgets for worst-case nights.
- Create response playbooks: when sensors hit warning thresholds, log the fix and note how long it restored setpoints.
Layer insulation before adding more heat
The cheapest BTU is the one you do not lose. Seal drafts, double up on glazing, and add internal thermal curtains to hold warmth overnight.
Structural upgrades
- Glazing: Switch to multi-wall polycarbonate or inflate double polyethylene layers to boost R-value.
- Sealing: Use foam gaskets around vents and weather-stripping on doors to stop cold infiltration.
- Thermal curtains: Deploy retractable energy curtains at dusk to keep radiant heat inside while allowing morning sun to warm the space.
Passive solar tactics
- Thermal mass: Line the north wall with black-painted water barrels or masonry to store daytime heat.
- Reflective insulation: Add foil-faced insulation to the north wall or behind benches to redirect light back to crops.
- Snow management: Clear accumulated snow quickly to maximize light penetration and prevent structural strain.
Balance heating with airflow
Heating alone is not enough. Stale, humid air invites mildew and reduces CO₂ levels. Maintain airflow even in freezing weather.
Heating game plan
- Use sealed-combustion gas heaters for efficiency and plant-safe exhaust.
- Stage electric radiant mats under propagation benches for spot heating.
- Install smart thermostats with night-setback modes to conserve energy while staying above crop minimums.
Ventilation and circulation
- Crack ridge vents or cycle exhaust fans for a few minutes every morning to release condensation.
- Run horizontal air flow fans around the clock to mix warm ceiling air with cooler floor air.
- Monitor humidity with connected sensors; maintain 60–75% for greens and 50–65% for fruiting crops.
Choose crops that match winter conditions
Align crop selections with achievable light and temperature levels. Use the quick reference below to balance production goals with resource demands.
| Crop group | Examples | Temperature targets | Notes |
|---|---|---|---|
| Cut-and-come-again greens | Spinach, mâche, claytonia, tatsoi | 45–65 °F daytime, 35–45 °F nighttime | Harvest outer leaves frequently; stagger sowings every 10–14 days to maintain succession. |
| Cold-hardy herbs | Parsley, chives, cilantro | 50–70 °F daytime, 40–50 °F nighttime | Use supplemental lighting to prevent bolting when day length drops below 10 hours. |
| Root crops in beds or bags | Carrots, hakurei turnips, beets | 45–65 °F daytime, 35–45 °F nighttime | Mulch soil with woven blankets to buffer temperature swings; ventilate to control condensation. |
| Fruit and blossom crops | Dwarf tomatoes, peppers, citrus | 60–75 °F daytime, 55–60 °F nighttime | Require active heating plus supplemental lighting; pollinate by hand or with oscillating fans. |
Sow successions every two weeks for leafy greens and store extra trays near the warmest zone to fill gaps quickly.
Build a winter monitoring routine
Frequent, lightweight checks prevent minor issues from becoming crop losses. Create a shared log and track the readings that matter most in cold weather.
Daily checklist
- Record min/max temperature and humidity readings from connected sensors.
- Inspect glazing seals, door latches, and frost buildup on vents.
- Scout for condensation on leaves and deploy fans or venting to dry the canopy.
- Verify automation schedules (vents, heaters, irrigation) and note any manual overrides.
Weekly tune-ups
- Calibrate thermostats and sensor probes; replace batteries before cold snaps.
- Flush irrigation lines to prevent mineral build-up from slower winter transpiration.
- Review energy consumption and adjust night-setback temperatures if crops allow.
- Update your seasonal playbook with lessons learned.
Bring it all together
Use the equipment blueprint to verify that your structure and climate systems can hit winter setpoints. Pair it with zone-specific crop plans, and you will move from emergency response to confident, year-round production.
Frequently Asked Questions
How warm should I keep a winter greenhouse?
Match temperature targets to your crop mix. Leafy greens stay productive at 45–60 °F, while fruiting crops need consistent temperatures above 60 °F. Use a min-max thermometer to confirm overnight lows and add thermal mass if dips fall below target.
Do I need grow lights during winter?
Supplemental lighting becomes essential once natural day length drops below ten hours or when you grow fruiting crops that demand high light intensity. Use full-spectrum LEDs to hit 200–400 µmol/m²/s for greens and 500+ for fruiting varieties.
How do I stop condensation and disease?
Ventilate daily, even on cold mornings. Open roof vents a few inches or cycle exhaust fans to purge moist air, then run horizontal air flow fans to keep leaves dry. Pair that airflow with sticky traps and weekly scouting for early pest detection.