How do I keep my greenhouse tent warm?

Keeping a greenhouse tent warm enough for plants to thrive can be challenging, especially during cold weather. There are several methods you can use to maintain the ideal temperature in your tent greenhouse so your plants stay healthy and productive all season long.

What temperature do greenhouse tents need to be?

The ideal temperature range for most greenhouse tent plants during the day is 65-75°F. At night, temperatures can drop to 55-65°F. These ranges provide enough warmth for active growth without stressing plants.

Seedlings and young transplants that are still establishing roots often need a warmer environment between 70-80°F. Once matured, plants can withstand slightly cooler temps down to 60°F at night.

Here are some optimal temperature guidelines for common greenhouse tent plants:

Plant	Day Temp	Night Temp
Tomatoes	65-80°F	60-70°F
Peppers	65-75°F	60-70°F
Lettuce	60-70°F	45-55°F
Cucumbers	65-75°F	60-65°F
Herbs	65-75°F	50-60°F
Seedlings	70-80°F	65-70°F

Aim to maintain temperatures in these ranges for optimal plant health and production.

Use an efficient greenhouse heater

A dedicated greenhouse heater is the most effective way to keep your tent warm. Greenhouse heaters are designed to safely and efficiently provide radiant warmth for enclosed growing spaces.

Small electric or propane greenhouse heaters are ideal choices for tent greenhouses. Look for a heater with enough BTUs to warm the total square footage of your tent space. Most tent heaters provide between 5,000-20,000 BTUs.

Position the greenhouse heater near the center of the tent so warm air can efficiently circulate. Have at least 1 foot of clearance around the heater and keep flammable materials away.

Use a thermostat controller to precisely regulate the greenhouse tent’s temperature. Aim to run the heater as needed to maintain your ideal temp range.

Considerations for greenhouse tent heaters:

• Electric heaters require an outdoor-rated extension cord and GFCI outlet.
• Propane heaters need proper ventilation to avoid buildup of fumes.
• Kerosene and natural gas tent heaters are also options but require more safety precautions.
• Choose a fan-forced or convection style heater for the best heat distribution.
• Heaters with automatic shut-off prevent overheating risks if tipped over.

Insulate the greenhouse tent

Insulating your greenhouse tent will help hold in heat and prevent cold drafts. Just like insulating a house, adding insulation to tent walls and roof helps regulate internal temperatures.

For easy insulation, wrap insulating bubble wrap or foam panels around the exterior tent walls. Secure with tape or clips. This provides an extra buffer between the inner tent space and cold outside air.

Using 2-3 layers of heavy-duty greenhouse plastic on the tent walls also improves heat retention. The twin layers of plastic trap heat and limit cold air intrusion.

Installing thermal curtains inside the tent is another good option for boosting insulation. Close the curtains at night to maintain warmer overnight temperatures. Open them during the day so sunlight can penetrate.

Tips for insulating a greenhouse tent:

• Add bubble wrap, foam panels, or straw bales around perimeter of tent.
• Use multiple layers of reinforced greenhouse plastic for tent coverings.
• Hang thermal curtains across interior to hold in heat at night.
• Seal any gaps, holes or openings with caulk or tape.
• Add plastic flaps over entrances to minimize cold air coming in.

Use heat retention materials

Certain materials used inside your greenhouse tent can retain and radiate heat to keep plants warmer at night. This passive solar heating reduces the need for as much active heating from your tent heater.

Stone and concrete blocks: Lining the tent floor with cinder blocks or bricks absorbs heat during the day. The stones release this warmth at night as temperatures drop. This makes the ambient tent air a few degrees warmer.

Water containers: Filling jugs, barrels or tubes with water provides thermal mass. The water absorbs heat which continues radiating out as it slowly cools down. Position water containers around the tent or near particularly cold-sensitive plants.

Black surfaces: Painting surfaces black increases heat retention as dark colors absorb more warmth. Paint the exterior of water containers black or use black propagation trays.

Tips for using heat retention effectively:

• Use rocks, concrete blocks or water tubes on the floor or shelving.
• Paint containers and surfaces black to amplify heat absorption.
• Add thermal mass such as stones or water by vents where cold air enters.
• Use removable materials to avoid overheating tent in warmer seasons.
• Manage water containers to prevent algae growth and mosquito breeding.

Seal air leaks

Sealing any air leaks in your greenhouse tent prevents warm air from escaping and cold drafts entering. This helps maintain steady temps so your heater doesn’t have to work as hard.

Check where the cover meets the frame and seal gaps with tape, caulk or insulation. Make sure Zippered doors close tightly and add flap coverings as needed. Seal vents and openings when not in use.

Also seal gaps around any cords, pipes or fittings that penetrate the tent cover. Stuff areas with insulation or use caulk/tape to close holes where air could leak through.

Tips for sealing a greenhouse tent:

• Apply clear caulk or weatherstripping tape on the tent frame.
• Check zippers and entrances for tight closure.
• Use flap door coverings with Velcro seals.
• Seal vents, ducting connections, and fittings.
• Check inside for gaps and seal with tape or caulk.

Manage the greenhouse tent ventilation

Proper ventilation is crucial in a greenhouse tent to maintain the ideal temperature range. While ventilation allows some cold air in, it’s needed to prevent overheating and provide air circulation.

Use vents, windows, or exhaust fans to manage ventilation. Close vents at night and on cold days to retain more warmth. Open vents just enough on sunny days to refresh the air without allowing too much cold air flow.

Aim for good air exchange but avoid having direct cold drafts blow on plants. Manage ventilation based on each day’s weather conditions.

Installing an evaporative cooler can provide necessary ventilation while also cooling the tent a few degrees in hot weather. The cooler blows air over water-saturated pads which has a natural chilling effect.

Tips for managing greenhouse tent ventilation:

• Open vents/windows fully during hot days, just crack open when cold.
• Close up tent at night to retain warmth.
• Use exhaust fans sparingly in cold weather to avoid sucking out too much heat.
• Adjust ventilation openings based on temperature readings each day.
• Consider adding an evaporative cooler to provide cooling airflow.

Use row covers and blankets

Adding an extra layer of protection over plants or along tent walls helps capture warmth inside your greenhouse. Floating row covers or thermal blankets limit heat loss from evaporation.

Drape fabric row covers directly over plants overnight to hold in warmth near the foliage. Support covers with hoops or frames to keep weight off of plants.

Insulated bubble wrap or weed blocking fabric can also attach to tent frames to create an insulating blanket around the inner walls. Remove during daytime hours.

Tips for using row covers and blankets:

• Use hoops to keep floating row covers from touching plant leaves.
• Secure tightly around edges to retain more warmth.
• Choose breathable fabric row covers to prevent moisture buildup.
• Use lightweight blankets that allow sunlight penetration during the day.
• Check that covers are not resting on or rubbing foliage.

Add supplemental heat sources

Small supplemental heating devices can provide an extra boost of warmth. When used with an electric or propane tent heater, extra heat sources help create a cozy greenhouse environment.

Portable space heaters: A space heater with automatic shutoff can add heat near plants that need a little extra warmth. Position safely away from plants and tent walls.

Heating mats: Placing seed trays or pots on a propagation heating mat helps maintain warmer soil temperature. This stimulates root growth.

Light bulbs: Stringing incandescent light bulbs over plants generates radiant warmth from the bulbs. Use the lowest wattage suitable for the covered area.

Tips for using supplemental heat sources:

• Only use portable electric or propane heaters with auto shutoff safety features.
• Place space heaters on stands so they are not risks for knocking over.
• Check that heating mats are designed for seed starting and propagation.
• Keep light bulbs a safe distance from tent walls, leaves or other flammables.
• Monitor closely to avoid overheating or fire hazards.

Use a backup power source

Power outages during cold weather can be detrimental for greenhouse tent plants. Having a backup power source keeps your heater and other electrical devices running if the power goes out.

Gasoline generators offer an affordable backup power option for most tents. Size the generator to handle the starting wattage of your heater and other connected devices.

Installing a small rechargeable battery bank with inverter provides backup power without the noise, fumes, and refueling of a generator. Hardwire an RV or marine battery bank to power critical equipment if the grid electricity fails.

Tips for using backup power:

• Choose backup systems capable of running your heater for several hours.
• Test that backup power seamlessly takes over during grid outages.
• Make sure exhaust from gasoline generators vents safely away from tent.
• Monitor battery charge level if using solar charged batteries.
• Run occasional maintenance tests to ensure readiness of backups.

Conclusion

Keeping your greenhouse tent warm doesn’t have to be difficult or energy-intensive. Using the right heater and insulation techniques allows you to maintain ideal conditions for thriving plants. Test different methods to find the best heating, insulation, and heat retention solutions for your unique tent setup and climate.

With the right preparations, you can continue growing a productive greenhouse garden even through cold weather. Pay close attention to conditions in your tent each day and make adjustments as needed. A cozy, warm tent environment will keep plants healthy while saving you time and money over having to replace frost-damaged plants.