How Greenhouses Stay Warm on Their Own

• Natural heat retention: Greenhouses trap sunlight during the day, and the warmth gets stored in the soil, water, and structures inside. At night, this heat gradually releases and helps maintain a higher internal temperature than the outside air.
• Boosting passive heat: Adding thermal mass like barrels of water or concrete blocks helps store extra warmth. Using double-glazed windows or twin-wall polycarbonate panels can also make a big difference in insulation. Make sure your greenhouse is facing the sun for most of the day to maximize heat gain.

What Affects the Need for Heating?

• Your local climate: If you live in a place where freezing nights and frost are common, your greenhouse will probably need a heater. In milder areas, you might get by with insulation and smart design.
• What you’re growing: Tropical crops like peppers and orchids need a warm environment year-round. Cold-hardy greens like kale or spinach can survive in much cooler conditions. Seedlings are more fragile and generally require stable, warm temperatures to grow well.
• The growing season: Greenhouses used only in spring, summer, or fall might not need extra heat. But if you want to grow during the winter months, especially in colder regions, a heating solution becomes important.
• Greenhouse design: Materials like thick glass and polycarbonate insulate better than thin plastic. Watch for any cracks or gaps where warm air might escape. Vents are great for airflow but can let out heat if not sealed properly during cold months.

When You Definitely Need Heat

• Freezing nights: If your local temperatures often dip below 32°F at night, you’ll need a heater to prevent frost damage.
• Starting seeds early: Seeds germinate best in a warm and stable environment, so a heater helps give them a strong start in late winter or early spring.
• Protecting sensitive plants: Tropical or subtropical plants won’t survive long cold spells. Heating lets you keep them healthy through winter.
• Growing for early harvests or flowers: If you’re trying to beat the season or produce flowers early for market, keeping the temperature steady is key.

Popular Heating Options for Greenhouses

• Electric heaters: These are user-friendly, reliable, and great for small to medium-sized greenhouses. Many come with thermostats and timers for easy control. Keep in mind they can be costly to run if electricity is expensive in your area.
• Gas or propane heaters: These provide strong, fast heat for larger spaces. Just make sure your setup has proper ventilation and that you’re using a greenhouse-approved model.
• Wood stoves: A wood-burning stove gives off solid radiant heat and is a great choice for larger setups. However, you’ll need to manage the fire and make sure there’s good smoke ventilation.
• Solar heating systems: Solar water or air heaters can be pricey upfront but are efficient in the long run. If your area gets good sunlight, this is a sustainable way to heat your greenhouse.
• Heat mats and soil warmers: Instead of heating the whole greenhouse, you can focus on the root zone. These tools are great for seed starting and use less energy overall.

Saving Money While Keeping Warm

• Use insulation: Greenhouse-grade bubble wrap works well to trap heat. Cover the walls and ceilings to reduce heat loss.
• Seal gaps and cracks: Prevent warm air from leaking out by sealing any holes or joints with weatherproof materials.
• Install thermostats: A programmable thermostat helps regulate heat more efficiently and avoids wasting energy.
• Cover plants at night: Thermal blankets or floating row covers can hold in extra warmth during cold nights.
• Group plants together: Warmth-loving crops benefit from being clustered, creating a mini microclimate that holds heat better.

Off-Grid Heating Ideas

• Composting inside or nearby: Compost gives off heat as it breaks down. A pile placed inside or next to the greenhouse can help keep temperatures up naturally.
• Thermal water barrels: These absorb heat during the day and release it at night, helping regulate the internal temperature.
• Cold frame inside the greenhouse: Adding a small insulated cold frame inside your greenhouse provides an extra layer of warmth for delicate plants.
• Digging into the ground: Walipinis, or partially underground greenhouses, take advantage of the earth’s steady temperature. They’re more work to build but can significantly reduce heating needs.

Wrapping It Up

So, do greenhouses need to be heated? It really depends on your goals, your local weather, and what you’re growing. Some gardeners can manage just fine with smart design and passive heat techniques, while others need heaters to get through the winter months. The good news is that there are options for every budget and setup—from electric heaters to compost-powered warmth.

The key is to stay aware of your greenhouse’s temperature, know your plants’ needs, and make sure everything is sealed up tight. With the right planning and tools, your plants can thrive all year long.

FAQs

Can I use a regular space heater from my house in my greenhouse?

It’s not recommended. Regular space heaters aren’t made for moist greenhouse environments and can pose safety risks. Use a heater rated for outdoor or greenhouse use.

What’s a good temperature range to aim for in winter?

Aim for 50°F to 75°F depending on the plants. Hardy crops can go lower, while tropical plants need it consistently warm.

How can I keep an eye on the temperature in my greenhouse?

Use a digital thermometer with high-low memory or a wireless setup that sends updates to your phone so you can monitor remotely.

Is summer overheating a problem for greenhouses?

Yes, it can be. Even in cooler climates, temperatures can skyrocket inside a greenhouse. Use roof vents, side vents, and shade cloth to keep things manageable.