Steps To Prepare A Texas Greenhouse For Winter

Preparing a greenhouse for winter in Texas requires a mix of region-specific planning, practical retrofit work, and an operational checklist you can follow when cold weather approaches. Texas is a large state with very different winter patterns from the Gulf Coast to the Panhandle. Still, the same basic principles apply: conserve heat, protect plants and infrastructure from cold, manage humidity and pests, and have contingency plans for unexpected freezes. This article walks through concrete, actionable steps, with numbers and timelines you can follow.

Understand Your Local Winter Risks

Winter in Texas ranges from mild nights in the Rio Grande Valley to occasional subfreezing events in North Texas and prolonged hard freezes in the Panhandle. Know your USDA hardiness zone and your average first and last freeze dates. Also factor in unusual events: Texas has experienced rare but severe freezes that can last multiple days.

Quick regional guidance

Coastal South Texas and the Lower Rio Grande Valley: rare frosts, focus on light protection and windproofing.
Central Texas and the Hill Country: occasional freezes; expect a few nights below freezing.
North Texas and Northeast Texas: more frequent freezes and short-duration cold snaps.
Panhandle and the Texas Panhandle region: frequent hard freezes and heavy cold risk; move to more aggressive insulation and heating.

Timeline: When To Start Winter Prep

Start in late summer to early fall. A staged approach avoids last-minute panic when a cold front hits.

August to September – plan, inspect structure, order supplies.
October – install insulation upgrades, clean and reorganize interior, start moving sensitive plants.
November – finalize heating, test systems, set up thermal mass and backups.
When a freeze warning is forecast – add row covers, circulate air, reduce irrigation frequency, monitor closely.

Structural Inspection and Repairs

A sound structure retains heat and reduces heater sizing and fuel costs. Walk around the greenhouse with a checklist.

Check for gaps and drafts at doors, vents, corners, and where panels meet the frame.
Inspect framing for rust, rot, or loose fasteners and tighten or replace as needed.
Verify glazing panels (polycarbonate, glass, polyethylene film) are intact; replace torn film or cracked panels.
Confirm that vents open and close and that latches and seals function.

Practical tips: use weatherstripping for doors and windows, apply silicone caulk around joints, and install a door sweep. For plastic film greenhouses, a new layer of plastic can save substantial heat loss.

Insulation and Thermal Retention

Insulation is the most cost-effective way to reduce heat loss. In Texas winters, adding a second layer of film and sealing gaps often yields big returns.

Covering and glazing options

Double-layer inflated polyethylene: creates an air gap that raises insulation value. Inflate to manufacturer guidelines and check regularly for leaks.
Rigid twin-wall polycarbonate: higher R-value and durable; good long-term upgrade.
Bubble wrap horticultural insulation: inexpensive for benches, walls, and odd-shaped areas; remove if humidity becomes an issue.
Thick horticultural foam board: useful for blocking wind on the north side or covering low vents.

Thermal mass

Water stores heat and releases it slowly overnight. Use dark-colored barrels or tanks and place them on the north side to avoid daytime shading.

Recommended: 55-gallon drums painted black; about one drum per 50 to 100 square feet can materially buffer temperature swings.
Placement: elevate slightly to allow air circulation; group drums for efficiency.

Heating: Sizing, Options, and Safety

Select a heating method appropriate to your greenhouse size, insulation level, and plant tolerance.

Heat loss estimate and heater sizing

A basic rule of thumb for greenhouse heat load is to calculate BTU per square foot based on insulation level:

Single layer polyethylene: 30 to 40 BTU per square foot for temperate to cold nights.
Double layer film: 20 to 25 BTU per square foot.
Insulated/good glazing: 10 to 15 BTU per square foot.

Example: a 400 square foot single-layer greenhouse might need 12,000 to 16,000 BTU of continuous heating capacity to keep above freezing during a cold night. These are estimates; use local climate data and consult an HVAC contractor for precise sizing.

Heating options

Propane or natural gas unit heaters: common for larger greenhouses; efficient but require ventilation and CO monitoring.
Electric resistance or infrared heaters: easy to install and safer indoors; higher operating cost but good for smaller spaces or supplemental heat.
Solar heating and passive solar: glazing, dark thermal mass, and insulated north walls reduce fuel needs, but rarely sufficient on their own during prolonged cold snaps.
Wood stoves: useful in rural setups but require care with ventilation and fire safety.

Safety and control

Use thermostats with minimum temperature set points and separate safety high-limit control.
Install a carbon monoxide detector if using combustion heaters.
Route exhaust outdoors, and ensure fresh air intake to avoid oxygen depletion.
Have a plan for fuel outages: portable electric heaters with a backup generator can save plants during sudden failures.

Ventilation, Air Circulation, and Humidity Control

Winter management is not just about heat. Humidity and stagnant air can increase fungal disease. Keep air moving and control humidity without losing excessive heat.

Install circulating fans to maintain even air and temperature distribution; run intermittently to avoid cold drafts on plants.
Manage humidity by reducing evaporative surfaces and removing standing water from trays and floors.
Use dehumidifiers if available, but balance energy costs. Vent briefly on warmer daytime hours to flush moist air.
Keep vents and louvers operable for quick purging if humidity spikes or pests increase.

Plant Care: Moving, Pruning, and Watering

Protecting plants is the single biggest goal of winter prep.

Move sensitive plants to the warmest area, usually near the heater and away from north-facing glazing that is coldest at night.
Group plants with similar temperature needs together to create microclimates.
Reduce watering frequency: plants use less water in cooler months; water in the warmest part of the day to allow roots to warm.
Prune dead or weak foliage to reduce pathogen pressure and improve air flow.
Harden off greenhouse-grown plants before putting them outside for cold snaps; sudden exposure can shock them.

Frost Protection Strategies

When a hard freeze is forecast, add layers of protection.

Row covers and frost cloths: drape over benches and frames. They add a few degrees of protection and reduce radiational heat loss.
Insulate ground-level pots with mulch or insulating boards to protect root zones.
Close vents and reduce openings as temperatures drop, but ensure some circulation to prevent CO buildup if using combustion heat.
Use space heaters or electric heating cables under benches for critical seedlings.

Irrigation and Plumbing Winterization

Pipes and hoses can freeze and burst. Take preventive measures.

Drain above-ground irrigation lines or blow them out with compressed air.
Insulate exposed pipes and use heat tape in areas that drop below freezing.
Install a frost-proof hydrant or locate valves inside the heated area.
For automated systems, winterize controllers but maintain occasional run cycles to prevent stagnation.

Pest and Disease Management for Winter

Cold weather does not eliminate pests; it can change pressure and increase disease risk.

Sanitation: remove dead plant material, clean benches and trays, and disinfect tools.
Monitor for pests: aphids, whiteflies, spider mites can persist; treat early with low-toxicity methods like insecticidal soaps or beneficial insects if possible.
Reduce overhead watering and manage humidity to prevent fungal outbreaks like botrytis and powdery mildew.
Rotate crops and avoid planting new susceptible crops immediately after an outbreak without cleaning.

Lighting and Supplemental Light

Short days reduce growth. For winter production or overwintering seedlings you may need supplemental light.

LEDs are energy-efficient, produce less heat, and can be targeted to crop spectra and intensity needs.
Time supplemental light to extend photoperiods for long-day crops; use timers and aim for consistent daylengths.
Position lights to avoid heat damage to leaves; maintain recommended distance from plant canopy for the chosen fixture.

Emergency Plan and Monitoring

Have a written and practiced emergency plan.

Keep a freeze kit: extra blankets, row covers, thermal tarps, portable heaters, fuel, extension cords rated for outdoor use.
Monitor temperature with remote sensors and alarms that alert you when temperatures approach critical thresholds.
Establish priorities for plant salvage: which species or beds are most valuable and what you will do first in a crisis.
Keep contact information for local suppliers, HVAC technicians, and emergency services.

Checklist: Practical Items to Buy or Prepare

Weatherstripping and door sweeps.
Double-layer poly film or bubble wrap insulation.
Thermal mass containers (55-gallon drums) painted black.
Heater sized for your greenhouse plus thermostat and CO detector.
Circulation fans and thermostatic controllers.
Row covers and frost cloths.
Insulation for pipes, heat tape, and a shop vacuum or compressor for line blowout.
Timers and LED supplemental lights if production requires.
Sanitation supplies: bleach or horticultural disinfectant, pruning shears, sticky traps.

Final Practical Takeaways

Start early: many insulation tasks are easiest in dry, warm fall weather.
Seal first, then heat: fixing drafts and adding thermal mass lowers long-term heating needs.
Use layered protection: combine insulation, heaters, row covers, and thermal mass for best results.
Monitor continuously: remote sensors and alerts save plants during unexpected cold snaps.
Prioritize safety: ensure combustion heaters are vented and monitored, and have CO detection in place.

Winterizing a greenhouse in Texas is manageable with planning and a few concrete upgrades. Whether you operate a small backyard structure or a larger commercial greenhouse, these steps will help you protect plants, reduce energy use, and maintain production through the cooler months.