6 Best Space Heaters For Small Greenhouses In Spring to Beat Late Frosts
Safeguard your small greenhouse from late spring frosts. This guide reviews the 6 best space heaters to keep your tender plants warm and protected.
There’s nothing quite like the gut-punch of seeing a week’s worth of beautiful, green seedlings turned to mush by a single unexpected frost. We’ve all been there, pushing the season just a little too early, only to be reminded that Mother Nature has the final say. A small greenhouse provides a buffer, but it’s not a magical forcefield against a late-season cold snap.
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Why Late Frosts Threaten Spring Seedlings
A greenhouse feels like a safe harbor, but its thin walls only offer a few degrees of protection on their own. Young seedlings, especially heat-lovers like tomatoes and peppers, have not yet developed the hardy cell structures to withstand freezing temperatures. A frost doesn’t just chill them; it freezes the water inside their cells, causing ice crystals to rupture the cell walls from the inside out.
The real danger is the false sense of security. You spend weeks nurturing these plants indoors, then move them to the greenhouse where they thrive in the daytime sun. But as soon as the sun goes down, that stored heat radiates away quickly. A clear, calm night is often the coldest, and it can drop temperatures below freezing inside the greenhouse, wiping out your entire season’s start in just a few hours.
Bio Green Palma Heater for Precise Control
When you’re trying to keep tender plants within a very specific temperature range, precision is everything. The Bio Green Palma is an electric heater built specifically for this job. Its main advantage is a highly accurate remote thermostat you can place right at plant level, ensuring the heater kicks on exactly when your seedlings need it, not when the air near the ceiling gets cold.
This level of control is perfect for preventing overheating, which can be just as damaging as a frost and wastes a lot of electricity. The downside, of course, is its reliance on power. You need a reliable, outdoor-rated electrical hookup. But for a greenhouse close to the house filled with valuable starts, the investment in precision pays off by eliminating guesswork and creating a perfectly stable environment.
Mr. Heater Buddy for Off-Grid Greenhouses
Not every greenhouse is conveniently located next to an outlet. For hoop houses at the back of the property or any off-grid setup, a propane heater like the Mr. Heater Buddy is a lifesaver. It’s portable, powerful for its size, and runs off common one-pound or larger propane cylinders, making it incredibly versatile.
The tradeoff for this freedom is responsibility. Propane heaters consume oxygen and produce carbon monoxide, so you absolutely must ensure adequate ventilation. Cracking a roof vent and a lower side vent is non-negotiable. It also requires manual oversight; you’ll be checking fuel levels and monitoring the temperature yourself, as its built-in controls are basic. Think of it as a powerful, portable tool for actively saving your plants, not a set-and-forget solution.
Dr. Infrared Heater for Efficient Radiant Heat
Most heaters warm the air, which then warms everything else. An infrared heater works differently. It emits radiant heat, which travels through the air and directly warms the objects it hits—your benches, your soil, and your plants. This is a far more efficient way to protect your seedlings, as you’re heating the things that matter most.
The Dr. Infrared Heater is a great example of this technology. It can make your plants feel warm even if the ambient air temperature is still quite cool, saving energy. The key is placement. Since it works by line-of-sight, you need to position it so it can "see" as many of your plants as possible. It won’t circulate air, so it’s best paired with a small fan to prevent cold spots from forming in the shadows.
Comfort Zone CZ442E for Micro-Greenhouses
Sometimes, all you need is a little bit of warmth in a very small space. If you’re working with a cold frame, a small 4×6 foot hobby greenhouse, or even just a covered shelf unit, a massive heater is overkill. A small, inexpensive ceramic fan heater like the Comfort Zone CZ442E is often the perfect tool for the job.
These little units are simple: they have a basic thermostat and a fan to push out a surprising amount of heat for their size. They are great for taking the edge off a frosty night in a well-sealed, tiny structure. Their limitation is power. Don’t expect one to heat a larger greenhouse; it simply can’t do it. But for targeted protection in a micro-environment, its simplicity and low cost are hard to beat.
iPower Electric Heater for Set-and-Forget Use
For a reliable, all-around workhorse, a dedicated electric greenhouse heater with an integrated fan and thermostat is an excellent choice. The iPower heater is a classic example of this design. It combines heating with crucial air circulation, which is a major advantage.
The built-in fan ensures that warm air is distributed evenly throughout the greenhouse, preventing the hot and cold pockets that can stunt or damage plants. This constant air movement also helps strengthen seedling stems and reduces the risk of fungal diseases like damping off, which thrive in still, damp conditions. It’s less precise than the Bio Green, but its combination of heating and air circulation makes it a fantastic, low-maintenance option for most small greenhouses with power.
Dyna-Glo Kerosene Heater for Power Outages
Your best-laid plans can be ruined by a power outage during a cold snap. This is where a fuel-burning emergency heater comes in. A kerosene heater like a Dyna-Glo can pump out an immense amount of heat, making it the ultimate backup plan for saving your crops when the electricity fails.
This is not a heater for everyday use. Kerosene heaters require significant ventilation to deal with fumes and oxygen depletion. They also lack precise temperature control, so your goal is simply to keep the greenhouse from freezing, not to maintain a perfect 65°F. It’s a powerful, loud, and smelly tool of last resort, but one you’ll be incredibly thankful to have when the lights go out on the coldest night of spring.
Key Safety Tips for Greenhouse Heating
Using any heater in a small, often plastic-walled structure requires serious attention to safety. Overlooking these basics can lead to a melted greenhouse or worse. No matter which heater you choose, these rules are fundamental.
Always remember to:
- Provide ample ventilation for any fuel-burning heater (propane or kerosene) to prevent carbon monoxide buildup. A CO detector is a wise investment.
- Place the heater on a stable, level, non-flammable surface like a concrete paver, not directly on soil or a wooden bench.
- Keep the heater a safe distance from flammable materials, including the greenhouse’s plastic sheeting, shade cloth, and dry plant matter.
- Use only heavy-duty, outdoor-rated extension cords for electric heaters. A standard indoor cord is a fire hazard.
- Ensure any electric heater has a tip-over safety switch that automatically shuts it off if it gets knocked over.
Ultimately, the "best" heater is the one that fits your specific greenhouse size, power situation, and budget. The goal is to have a reliable plan in place before the forecast turns sour. Because a little preparation is all that stands between a thriving spring garden and the hard lesson of a late frost.
