6 Best Heating Covers For Small Greenhouses That Prevent Frost Damage
Shield your small greenhouse from frost. We review the 6 best heating covers, from thermal blankets to insulated films, for ultimate plant protection.
You check the forecast and your heart sinks; a late spring frost is rolling in tonight, threatening the tender seedlings you’ve nurtured for weeks. Protecting a small greenhouse from a sudden cold snap is a challenge every grower faces, and having the right tools on hand makes all the difference. The goal isn’t just to cover your plants, but to create a stable microclimate that shields them from damaging ice crystals.
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Key Features in Greenhouse Frost Protection
When you’re looking at frost protection, it’s easy to get bogged down in options. The first thing to consider is the material’s weight and light transmission. A heavy, opaque tarp will block frost, but it will also block precious morning light and can crush delicate plants if not supported.
Look for materials specifically designed for horticultural use. These are often called "floating row covers" or "frost blankets." They are lightweight enough to rest directly on many plants and are permeable, allowing air and some moisture to pass through while trapping a crucial layer of insulating air. The key is finding the right balance between insulation and letting the plant breathe and receive light.
Finally, consider ease of use. Are you trying to cover a 4×8-foot raised bed inside your greenhouse or the entire structure? A giant, unwieldy sheet might be great for insulation but a nightmare to deploy quickly on a cold, windy evening. Sometimes, having a few smaller, manageable pieces is far more practical than one massive cover.
Agfabric Floating Row Cover for Versatility
Protect plants from frost, pests, and sun with this breathable, lightweight 10 ft x 30 ft garden fabric. Use it directly over plants or with hoops to extend your growing season.
The Agfabric floating row cover is the jack-of-all-trades in the frost protection world. Think of it as a lightweight, breathable bedsheet for your plants. It comes in various weights, typically from 0.5 oz to 2.0 oz per square yard, which determines the level of frost protection it offers.
This cover’s main advantage is its versatility. You can drape it directly over low-growing crops like lettuce or strawberries, or you can support it with simple wire hoops to create a low tunnel inside your greenhouse. This "greenhouse-within-a-greenhouse" effect is incredibly effective. Because it’s so light, it allows a high percentage of sunlight to penetrate, so you can often leave it on for a few days during a cold spell without starving your plants of light.
The tradeoff, of course, is heavy-duty protection. A lightweight Agfabric cover might give you 2-4 degrees of frost protection, which is perfect for a light frost. It won’t save your tomatoes from a hard freeze in the low 20s. It’s a tool for managing the shoulders of the season, not for overwintering in a blizzard.
Sun Master Greenhouse Film for Heat Retention
Your first and most important "cover" is the skin of the greenhouse itself. Not all greenhouse films are created equal. Upgrading to a 6-mil, 4-year film with an infrared (IR) additive is one of the smartest investments you can make for heat retention.
Standard greenhouse plastic allows heat to radiate out and escape as soon as the sun goes down. An IR-additive film acts like a one-way gate for heat. It lets shortwave solar radiation in during the day, but it blocks the longwave infrared radiation (heat) from escaping at night. This simple feature can keep your greenhouse several degrees warmer overnight without any active heating.
This isn’t a blanket you throw on; it’s a foundational choice. When you’re building or re-covering your structure, choosing the right film is your primary defense. A well-sealed greenhouse with IR film is a passive heat sink, dramatically reducing the need for supplemental covers or heaters. It works silently in the background every single night.
Bio Green PAL 2.0/US Palma Greenhouse Heater
Sometimes, a passive cover just isn’t enough. When temperatures plummet, you need to add heat, and a small electric heater designed for greenhouses is the safest and most effective way to do it. The Bio Green Palma is a workhorse for small structures, combining a heater with a fan.
The fan is the critical component here. It circulates air throughout the greenhouse, preventing cold spots from forming and ensuring the heat is distributed evenly. Without a fan, the heat simply rises to the peak of the greenhouse, leaving your plants at ground level in the cold. A good thermostat is also non-negotiable; you want the heater to kick on only when it drops below a set temperature, like 35°F, saving electricity and preventing your greenhouse from overheating.
Of course, this requires a reliable power source and adds to your utility bill. It’s not a set-it-and-forget-it solution for an unpowered hoop house far from the house. But for a backyard greenhouse, a small, thermostatically controlled heater is the ultimate insurance policy that makes all your other covers more effective. It turns your protected space into a truly climate-controlled environment.
Planket 10’x20′ Frost Protection Blanket
If the Agfabric cover is a bedsheet, the Planket is a comforter. It’s a thicker, heavier frost blanket designed for a bit more protection. While still breathable, its primary function is insulation during a more significant cold snap.
Because of its weight, you wouldn’t typically float this directly on top of very fragile seedlings. It’s better suited for draping over sturdy plants like kale or rosemary, or for covering a cold frame or a low tunnel structure. The included grommets make it easy to secure against wind, which is a major plus. A flapping cover can do as much damage as the frost itself.
Think of this as your second line of defense. On a night with a predicted light frost, the Agfabric might be enough. When the forecast calls for a harder freeze, you’d pull out the Planket to lay over your most valuable or vulnerable plants inside the greenhouse, giving them that extra layer of insulation right where they need it.
VIVOSUN Soil Heating Cables for Root Zone Warmth
Give your seeds and plants a warm start with this 100ft soil heating cable. The built-in thermostat maintains a consistent 131°F/55℃ temperature, ideal for indoor or outdoor use in cold weather.
We often focus on protecting leaves from frost, but cold soil can be just as damaging, especially for young roots. Soil heating cables are a brilliant tool for providing targeted warmth directly to the root zone, which is far more efficient than trying to heat the entire air volume of a greenhouse.
These are essentially waterproof, insulated wires that you bury a few inches deep in your raised beds or lay underneath seed trays on a propagation bench. Controlled by a thermostat, they gently warm the soil to a desired temperature, promoting root growth and protecting plants from the shock of cold soil even when the air temperature is low.
This is a game-changer for starting seeds early in the season. Warm soil encourages rapid germination and strong root development, giving you a huge head start. For overwintering tender perennials like citrus or figs in pots, placing the pots on a surface heated by these cables can be the difference between survival and death. Protecting the roots is often the most critical battle.
Gardman 4-Tier Mini Greenhouse as a Cold Frame
Sometimes the best way to protect your most vulnerable plants is to give them their own little house. A small, tiered greenhouse unit like the Gardman model serves as an excellent cold frame, especially when placed inside a larger, unheated greenhouse.
This "nesting doll" approach creates multiple layers of insulation. The outer greenhouse blocks the wind and traps some solar gain. The inner mini-greenhouse traps another layer of air, significantly buffering the plants inside from the coldest temperatures. This is the perfect spot for hardening off tender seedlings before they go into the garden or for protecting a collection of prized succulents.
The clear plastic cover on these units is thin, so it doesn’t offer a huge amount of insulation on its own. Its real power is in creating that still, protected air space. On a truly frigid night, you can easily drape a frost blanket (like the Planket) over the entire unit, creating a super-insulated pod for your most precious plants.
Combining Covers and Heaters for Best Results
The most resilient frost protection strategy doesn’t rely on a single product. It’s about creating a layered system that you can adapt to the specific threat. No single cover or heater is a silver bullet; they work best as a team.
Your first layer is a well-sealed greenhouse with a high-quality IR film. That’s your passive defense. Your second layer is internal covers, like draping Agfabric over sensitive greens or using soil heating cables under your seed trays. This is targeted, efficient protection.
The final layer is active heating. A small, thermostatically controlled heater is your emergency backup. You set it to 35°F and hope it never has to turn on. But if a polar vortex dips south unexpectedly, that heater will be the hero that saves your entire season’s work. By combining passive heat retention, targeted insulation, and an active heat source, you build a robust system that can handle whatever the weather throws at you.
Ultimately, preventing frost damage is about proactive planning, not reactive panic. By understanding the strengths and weaknesses of different tools and layering them into a cohesive system, you can face a dropping thermometer with confidence. A little preparation ensures your hard work in the greenhouse pays off, season after season.
