Cooling a greenhouse in Texas requires a mix of passive design, active systems, and careful plant management. Texas summers can produce prolonged days above 95 F (35 C), intense solar radiation, and varying humidity depending on region. That combination stresses plants, accelerates water loss, and increases disease pressure. This article outlines practical, proven strategies — from low-cost retrofits to system-level solutions — so you can keep plant temperatures and stress levels under control while managing water use and operating costs.
Texas is large and climatically diverse. Western Texas is arid and hot, central Texas is hot with moderate humidity, and eastern/gulf-coast Texas is hot and humid. Cooling approaches that work well in dry climates (evaporative coolers) are less effective in high-humidity zones. Before committing to equipment, clarify:
Answering these lets you choose the right mix of shading, ventilation, evaporative cooling, and automation.
Passive measures reduce incoming solar energy and improve airflow. These are low-tech, cost-effective, and should be the first upgrades you implement.
Orient long sides of the greenhouse east-west to reduce midday solar load on sidewalls. Use glazing materials that balance light transmission and heat control: twin-wall polycarbonate provides better insulation than single-pane glass and cuts radiant heat gain.
Seal gaps to avoid uncontrolled hot spots, but ensure vents remain operable. Add insulating covers for nights when cooling isn’t needed but that can be retracted in the early morning to allow heat to escape.
Install shade cloths over the structure or on the roof. Shade cloth is rated by percent light reduction:
Use retractable shade systems when possible so you can adapt to seasonal needs. Exterior shading is more effective than internal because it prevents heat from entering the greenhouse in the first place.
Whitewash or reflective roof paint (shade paint) is an inexpensive option. Apply in spring; it reflects sunlight and reduces peak temperatures. It is temporary and often reapplied annually.
Thermal mass (water barrels, concrete benches) moderates temperature swings by absorbing heat during the day and releasing at night. In Texas heat, thermal mass reduces daytime peaks and can help avoid plant heat stress during sudden spikes.
Pair thermal mass with night ventilation: if nighttime temperatures drop significantly, open vents and run fans to dump accumulated heat before morning.
Ventilation moves hot air out and draws cooler air in. Properly sized ventilation is critical.
Ridge vents and sidewall vents use stack effect and wind to exchange air without electricity. For new builds or retrofits, install continuous ridge vents and adjustable side vents. Use thermostatic vent openers for automatic operation.
Exhaust fans provide reliable, controllable air exchanges. Select fans based on greenhouse volume. Use this formula to calculate air exchanges per hour:
exchanges per hour = (CFM * 60) / greenhouse volume in cubic feet
Aim for 30-60 air exchanges per hour on very hot Texas days; 40-60 is a practical target for reducing peak daytime heat. Choose intake louver placement low on the opposite wall to ensure full airflow across plants.
Consider fan staging and variable-speed drives so fans ramp up as temperature rises rather than running full-speed constantly.
Place fans high on hot walls to expel warm air and have intake louvers low to draw cooler air across plant canopy. Use circulation fans inside to eliminate microclimates and prevent pockets of stagnant, hot air. Cross-ventilation is far more effective than single-point exhaust when natural breezes are present.
Evaporative cooling reduces air temperature by evaporating water. Performance depends heavily on ambient humidity.
Pad-and-fan systems pull air through wetted pads, lowering temperature via evaporation. They are highly effective in dry interior Texas but less useful near the Gulf where humidity is already high.
Pad maintenance is essential: replace pads seasonally, keep pumps clean, and treat water to avoid scale and algae. Design pad area and fan capacity so intake air velocity through the pad is in the manufacturer-recommended range; undersizing reduces cooling, oversizing wastes water.
Fogging produces very fine droplets that cool air with minimal canopy wetting, making it better where foliar disease is a concern. Misting delivers larger droplets and can wet foliage, increasing disease risk.
Use fogging sparingly in humid zones and ensure droplet size and cycle programming are appropriate. Excessive humidity from any evaporative system increases fungal and bacterial disease risk.
Evaporative cooling uses significant water. Monitor water quality: high-salinity water leaves residues on pads and foliage and reduces pad life. Consider filtration and periodic pad flushing.
Internal thermal screens reflect infrared radiation and reduce incoming heat. Use aluminized screens to reflect heat during the hottest parts of the day, and retract them to maintain light levels when needed.
Dual-purpose screens (shade + insulation) reduce daytime heat and improve nighttime heat retention, cutting energy costs if you use supplemental cooling/heating.
Cooling always involves plant management choices. Some practical tactics:
Temperature and humidity sensors, wired or wireless, are indispensable. Use a control system to automate:
Program set-points with hysteresis to avoid rapid cycling. Logging data helps you refine strategies season-to-season.
Regular maintenance keeps cooling systems effective and safe.
Small hobby hoop house (10 x 20 ft): Start with a 24-30 inch circulating fan and passive shade cloth (30-50%). Add a small exhaust fan if temperatures exceed target frequently.
Medium hobby greenhouse (20 x 40 ft): Install ridge vents, side vents with thermostatic openers, two circulation fans, and an exhaust fan sized to achieve 30-50 air exchanges per hour. Consider a pad-and-fan only if your location is dry and water is available.
Commercial greenhouse: Professionally sized exhaust fans and pad systems, integrated controllers, and automated shade screens. Expect higher capital costs but greater control and crop yield consistency.
Costs vary widely: shade cloth and paint are low-cost (hundreds of dollars), fans and vents are mid-range (hundreds to a few thousand), and full pad-and-fan or automated systems can be several thousand to tens of thousands depending on scale.
Cooling a greenhouse in Texas requires layered solutions: reduce heat entry first (shading, reflective coatings), then maximize controlled air exchange (ventilation and fans), and use evaporative cooling only where humidity and water make it effective. Combine passive and active approaches with automated controls and good maintenance to protect crops and manage operating costs. Tailor measures to your specific Texas region, greenhouse size, and crop needs — the right mix will keep daytime peaks manageable and crops productive even in extreme heat.