Greenhouse Ventilation in Winter: How to Protect Your Plants

Why Winter Ventilation Matters

Proper greenhouse ventilation isn’t just for the summer months. In winter, fresh air is just as important for preventing mold, fungal diseases, and stagnant humidity. Without it, plants can grow slowly, become weak, or even die, especially in heated greenhouses where warm, moist air tends to build up.

How to Ventilate Without Losing Heat

The key in winter is to introduce fresh air gradually so you don’t shock plants with freezing drafts. Plan at least 2–3 short ventilation sessions a day rather than one long airing. Monitor humidity and temperature, and open vents just enough to exchange stale air.

Where and How Cold Air Should Enter

Install or use vents placed high up, near the roofline. This allows incoming cold air to mix and warm before it reaches plants. Whenever possible, use a small fan heater or duct to pre-warm the incoming air, it keeps leaves and fruit from frost damage and helps circulate oxygen evenly through the greenhouse.

Balancing Heat and Fresh Air

Always turn on your heating system before you ventilate. Keep it running as you open the vents so the fresh air is tempered. After ventilation, you can let the temperature drop slightly; well-built greenhouses hold heat, so running heaters 24/7 isn’t necessary. Use a thermometer and hygrometer to monitor conditions and switch heaters on only as needed.

Energy-Saving Tips

• Pre-warm incoming air with a fan heater or radiant unit to avoid temperature spikes.
• Use short, frequent airing instead of one big ventilation to minimize heat loss.
• Seal leaks and insulate non-vent areas to keep warm air where it belongs.
• Track temperature and humidity: modern greenhouse sensors make this easy and prevent overuse of heaters.

With these practices, you’ll maintain healthy air circulation, control humidity, and keep energy costs down, even in the coldest months.