Updated at: 15-06-2022 - By: Sienna Lewis

If you have a greenhouse and reside in a colder climate, you may be interested in learning how to heat a hobby greenhouse without spending a penny. When it comes to heating your greenhouse, nothing beats making the most of the available sunshine. In the end, it’s both cost-free and effective.

On the other hand, there are instances when the sky is overcast or it is pouring rain. In addition, the amount of sunlight you get in the winter is much reduced. The good news is that there are a number of ways to keep your greenhouse warm without breaking the bank.

Here are three simple methods for getting free heat for your greenhouse:

Quick Intro to Greenhouses

Native plants in each climate zone are adapted to the local day duration and temperature ranges. Growing delicate plants that are native to warmer regions can be done successfully in a greenhouse if you reside somewhere with harsh winters. Your yard becomes an exotic tropical paradise when you have one of these structures in your yard. Your planting options are nearly limitless once you grasp the fundamentals of heating greenhouses and controlling lighting and air flow.

How to Heat a Hobby Greenhouse for Free in 3 Easy Ways - Krostrade

What is a Greenhouse?

An enclosed greenhouse is one that has at least some of its structure made of translucent material. Although electromagnetic radiation from the sun can enter through the greenhouse’s walls and boost the air’s temperature, warm air cannot escape through the greenhouse’s walls. To help tender plants develop, mankind have been utilizing translucent materials since they were invented.

It wasn’t until the early 1400s in Korea that people learned they could increase the sun’s heat and open up more agricultural options by using heated greenhouses. Farmers have been able to accurately manage the temperature, humidity, and chemical composition of the greenhouse atmosphere for generations because to advances in winter greenhouse technology. The agriculture industry throughout the world relies significantly on automated greenhouse heating systems with digital controls and precise air circulation.

Greenhouses Can Be Any Size

Cold frames and hoop houses are also known as greenhouses, even though they don’t have movable walls. If a springtime cold snap is forecast, even the most casual gardener may cover a fresh lettuce seedlings with row covers. Miniature greenhouses, or “cold frames,” are produced by covering a single planting bed with a glass or plastic canopy.

Where to start

There are several ways to keep your greenhouse warm in the winter without spending any money.

However, the most crucial step is to ensure that any heat generated or received in your greenhouse is not lost.

Bubble wrap is an inexpensive and effective way to insulate your greenhouse. There is nothing better than a large number of bubbles. It’s better to use horticultural bubble wrap because it’s more durable than most other bubble wrap, but if you have some bubble wrap lying around, you can use it. You’ll simply have to replace it more frequently.

To insulate your greenhouse using bubble wrap, place the bubble wrap on the greenhouse’s inside surface.

There are several free ways to heat your greenhouse when it has been properly insulated, including:

  • Sunlight-generated heat
  • Thermogenic Mass
  • Compost

These are all free ways to keep your greenhouse warm over the winter. It’s possible to boost the temperature in your greenhouse using any of these methods, although some of them are more effective than others.

Advantages of Greenhouses

Greenhouse technology has a significant impact on northern countries’ food supply, as produce from vast greenhouse complexes is flown throughout the world. Having access to a greenhouse in the winter has two primary advantages for a home gardener:

  • It allows native plants to have a longer growing season. It can be difficult to mature home-grown tomatoes in the Pacific Northwest because of the short, chilly summers. You can start seedlings in a greenhouse even though it is still frosty outdoors. So they won’t get mildewed in the summertime when it’s raining and they’ll keep producing juicy red tomatoes even after October’s freezing temperatures has browned the outdoor plants.
  • A greenhouse allows you to cultivate a greater range of plants from around the world. It’s always a problem for northern vegetable gardeners to ripen summer crops like melons and eggplant. In a chilly climate, most citrus trees are out of the question, but they can survive in a greenhouse. Moreover, we haven’t even mentioned the flowers that you’ll be able to enjoy throughout the winter. If you build a greenhouse heating system with grow lights, you’ll be able to grow summer flowers at any time of year. A greenhouse’s enlarged possibilities can benefit anyone with a particular botanical interest, whether you’re an orchid enthusiast or a herbalist.

Protection from Precipitation and Wind

It’s a common occurrence for gardeners to see sensitive plants damaged by torrential rains. You may find that your tulips have been drooped to the ground by heavy rains, and a covering of snow can ruin an entire spring garden. Greenhouses let you control the climate. A solar heater or a variety of other natural heat sources can be used in conjunction with an electric heater to provide the ideal growing conditions that you desire.

Tip #1. Take advantage of the sun and make sure to insulate

The sun, as previously stated, is the most straightforward approach because it is a free source of energy and will always provide you with heat. It is easier to use the light to heat your greenhouse in summer, but it is more difficult for gardeners to get enough sun in the winter.

Place your greenhouse in a sunny, un-shaded location to get the most out of the sun’s heat during the colder months. Adding insulation to your greenhouse is also essential.

Transparent acrylic is an excellent choice for insulating your greenhouse while still allowing sunlight to pass through. You can use horticultural plastics to insulate your workspace, but bubble wrap will suffice.

Tip #2. Add thermal mass

Adding thermal mass to your greenhouse is one of the most cost-effective ways to generate heat. Thermal mass stores heat during warm weather, and once the weather cools, the mass will slowly release the heat is stored.

This is one of the most cost-effective ways to generate heat in your greenhouse. When the weather is warm, thermal mass stores heat, and when the temperature drops, the mass slowly releases the heat it has stored.

Heat can be stored in dark water barrels. When the temperature dips at night, the water barrels in your greenhouse will transfer the heat into your greenhouse, keeping your plants warm and toasty. Natural heaters can also be made from darker stones. During frigid nights, they discharge the heat they’ve stored up from the sun’s rays. Straw can be used to insulate the ground or soil in your greenhouse, making it even more energy-efficient.

Water barrels offer the greatest heat capacity of all thermal mass alternatives. Adding as many thermal mass options as you like to your greenhouse will yield the best outcomes. However, keep in mind that an overheated greenhouse is the absolute last thing you want.

Tip #3. Use Compost

As well as being able to absorb heat, compost may also produce heat. Now that we’ve established what compost is, how do we use it? Adding organic items, such as food scraps, animal products, dried leaves, etc., to the soil is a common practice for gardeners. As it decomposes, compost releases heat into the soil.

In addition to providing heat for your greenhouse, compost improves the quality of the soil, resulting in a more nutritious crop. Your compost pile should be situated centrally in the building’s greenhouse. As a result, your greenhouse will be heated from the center.

Compost has the drawback of attracting rats and odor (particularly if animal products are used). Use compost in an enclosed greenhouse if you intend to do so.

Why Use a Mini Greenhouse for Your Plants?

For those who want to grow a variety of crops, a compact greenhouse is ideal. If you’re still undecided about purchasing a micro greenhouse, here are some of the benefits:

Shield your plants from unwanted pests and blight

There are a variety of creatures and insects that would love to devour your leaves. Your neighbor’s plants may also be infected with contagious plant diseases, which can then spread to yours. Plants can be protected from undesired pests and plant diseases if they are housed in an enclosed tiny greenhouse, though.

Protect your crops from bad weather

Plants are readily destroyed by storms, heavy rain, strong winds, and hot temperatures. Growing your plants in a greenhouse is a good idea if you live in a region with erratic weather. Your plants will be safe and toasty no matter what the weather is like outside.

Great for gardeners with limited space

You can grow practically any kind of plant in a hobby greenhouse, even if you don’t have a garden because of your passion for growing. A hobby greenhouse can be placed on a patio, deck, or balcony.

Extend the growing season

Your crops can be grown all year round in a compact greenhouse, allowing you to start planting before the cold season arrives. When the weather improves, you can move your plants into your garden and begin harvesting earlier than you had originally planned.

How to Heat a Small Greenhouse

The good news is that there are several simple choices for greenhouse heating if you want to start out modestly with year-round horticulture. If you have just a few delicate plants to preserve, you can easily turn your garden beds into cold frames. Simple plastic sheeting or glass panes can be placed on top of the bed to provide adequate protection from the cold during the winter months. If the sun gets too hot, it’s a good idea to build these so that the roof or row cover can be raised up.

Heat Your Greenhouse with Direct Solar Energy

The north wall of your little greenhouse should face your house’s south side if you want to keep it warm. By building an addition that faces south, the greenhouse doubles as a source of heat to keep your home warm and saves you money on heating costs. An object that absorbs heat and gently releases it over time is called a “heat sink.”

Using the Sun as a Passive Heat Source

The primary source of heat for a greenhouse made of plastic or glass is the sun’s rays illuminating the walls. Every thing inside the greenhouse, including any huge thermal mass you may have placed inside, will be heated by the sun’s electromagnetic radiation. Many gardeners utilize 55-gallon barrels filled with water as a form of thermal mass. The translucent walls of your greenhouse can also be insulated with bubble wrap to capture as much warm air as possible during a cold winter. This common, low-cost material is great for greenhouse insulation and is probably lying around your house from packages you’ve received via mail order.

A Beginner's Guide to Using a Hobby Greenhouse ~ Homestead and Chill

Electric Heaters for Your Small Greenhouse

Small greenhouse heating costs are low, and you may only need it for a few hours on chilly nights if you have a thermostat or an automatic timer. Gardeners who have to be away from their plants during the day will appreciate how easy it is to use this heating system. You can leave a tiny space heater on a thermostat and not worry about it turning on until you need it. Automatic shut-off features, such as those that activate if the heater tips over or becomes excessively hot, are also standard on today’s heaters. The ability to approach your gardening endeavor like a farmer by utilizing latest digital greenhouse heater technology is an invaluable asset.

How to Heat a Greenhouse for Free

It’s a good idea to start with the free options when deciding how to heat greenhouses. As a last resort, you can use an electric heater if you’ve exhausted all other sustainable options for keeping your greenhouse warm.

Positioning Your Greenhouse

As previously indicated, the ideal strategy to capture solar energy is to position your greenhouse so that the south facing side faces directly into the sun. Throughout the northern hemisphere, the winter sun never rises over the horizon in the north.

Store Warmth in a Thermal Mass

Having positioned your greenhouse to take advantage of all that free winter sunlight (when it’s available), the next step is to figure out how to keep the heat you’ve accumulated in your greenhouse. An object that can absorb and store a lot of heat is called a thermal mass. Gardeners commonly use 55-gallon water drums in their greenhouses to prevent sudden temperature dips after sunset. Another option is to utilize cinder blocks to construct the greenhouse’s north wall, which does not receive much direct sunlight. During the day, these blocks will absorb heat from the greenhouse’s heated air, and at night, they will gently radiate that heat back out. On chilly evenings, using massive heat sinks like water, stone, cement, and the like is a smart idea.

Pay Attention to Insulation

The next stage in achieving energy-efficient heating is to check for any air leaks. In spite of the fact that a greenhouse requires some level of air circulation, you want to be able to regulate the flow by adding a number of strategically placed vents or holes. You don’t want to create chilly areas in your greenhouse by allowing it to leak accidentally. When it comes to insulating transparent glass greenhouse walls or doubling up against plastic sheets, bubble wrap is an excellent choice. Like a puffy down jacket, the air in the bubbles acts as an excellent insulator.

Row covers of horticultural fleece can also be used to insulate your greenhouse’s plants.

Passive Heating May be Enough

If you’re lucky enough to live in a mild environment, you won’t need to add any additional heat sources after using the techniques described above to keep your greenhouse toasty. If you live in a region where temperatures don’t fall below freezing, bubble wrap insulation and a few water buckets may be enough to preserve sensitive plants. In order to prevent your plants from being overcooked, you may need to open up vents and let hot air out. Even on a mild day, imagine how hot an automobile becomes when left parked in the sun.

How to Heat a Greenhouse for Cheap

Compost piles produce natural free heat, which can be used in your greenhouse as a secondary heating source. If you’re considering a tiny greenhouse because you’re a serious gardener, you’ve probably already started composting your kitchen scraps and other organic waste. If you’ve got a backyard compost pile, you’re already ahead of the game. Cornell University is working with commercial farmers to help them use compost as a primary heat source for barns and large greenhouses. One 10-gallon pile, or two large plastic buckets, can reach temperatures of exceeding 120 degrees Fahrenheit if left alone for too long.

To be on the safe side, keep in mind that fly larvae, weed seeds, and thermosensitive diseases will all perish at temperatures above 104 degrees Fahrenheit. “Thermophilic phase” describes this first, intensely hot stage, which can endure for weeks or even months. Every day, for a few days, rotate your compost pile so that the cooler, outside sections have a chance to warm up before re-entry. Through conduction, convection, and radiation as well as moisture from a sufficiently wet compost pile, a compost pile can provide a substantial humidity boost to the greenhouse environment.

Greenhouse Heating Through Combustion

The next heating method to consider as we go over the numerous greenhouse heater alternatives are heaters that utilize some form of fuel. C02 management is made more difficult in a closed greenhouse setting by combustion heaters. In order to build a safe vent or chimney out of a greenhouse’s plastic or glass framework, one must have construction experience. Fuel-burning heaters are available from the following manufacturers:

  • A natural gas heater is unlikely to be available from your utility company unless you’re creating an integral greenhouse (such as converting a sunporch). Your greenhouse can be heated by a propane tank that is connected to a propane heater. It is vital to safely burn propane that it be vented to the outside using a safe method that ensures the gas is not combustible.
  • Using kerosene or paraffin, these heaters suck liquid fuel up through a wick that’s lit. Even though they normally have a safety device that extinguishes them if they fall over, they’re still considered a major fire hazard because of that. They are. This type of heater must be used in an area with adequate outside airflow because it emits pollutants into the air (such as carbon monoxide, nitrogen oxides, sulfur dioxide, polycyclic aromatic hydrocarbons, and phthalates).
  • Small wood burners can be used to heat greenhouses without using fossil fuels. If you can get your hands on some firewood, this is a great method to supplement your greenhouse’s heating system on a more regular basis. When it comes to heating your greenhouse, wood burners aren’t the ideal option because they require a lot of time and effort. In addition to gathering and transporting firewood, maintaining a well-burning fire takes frequent attention. The chimney (which can get extremely hot) must also be suitably insulated where it goes through the greenhouse’s framework.
  • A lot of homesteaders who want to grow food in huge greenhouses as part of a sustainable lifestyle are enthusiastic about the energy efficiency of the rocket mass heater. Rocket mass heaters are incorporated into a building’s original design. A massive mass of brick or masonry is embedded with a high-temperature combustion chamber where wood is burned. Combustion gases are routed through the masonry, which heats and radiates the entire thermal mass for a long period of time.

Energy-Efficient Ways to Heat Your Greenhouse

The finest greenhouse heating system is one that can adapt to changing temperatures on-the-fly. Because you can keep sensitive plants in your greenhouse throughout the year, you won’t have to use the heaters as often. Passive solar energy and perhaps a heated compost pile, paired with bubble wrap insulation, are typically enough to keep a backyard greenhouse warm practically constantly. An electric heater is a safe and energy-efficient choice for those extra-cold evenings when you need to keep your delicate plants from freezing.

Avoid the Need for Venting in Winter

Trying to utilize a gas heater that needs to be vented to warm an enclosed environment like a greenhouse in subzero temperatures can be counterproductive. If you want to create an inside microclimate, don’t rely on such external heat solutions. They work great in open settings like campgrounds. When the temperature dips below a specific level, thermostat-controlled electric heaters are activated.

Electric Heaters with Fans Promote Healthy Air Flow

It is a problem that every greenhouse owner has to deal with. Mold and mildew thrive in a greenhouse if the air is too quiet. When there is no breeze, moisture accumulates on vegetation and other surfaces, making it difficult for it to evaporate. It is possible to alleviate this problem in the summer by opening roof vents and allowing heated air to rise and escape, while bringing cooler air in through floor vents. To keep warm, you’ll need to keep your home sealed during the winter, which increases your risk of mold growth. On the coldest days of the year, an electric heater with a fan can keep the air moving in your greenhouse. Large greenhouses can benefit from garage and workshop heaters, which circulate warm air evenly throughout the structure and help eliminate cold patches.

Heating Your Greenhouse Safely

Any heat source you use in your backyard greenhouse must be completely safe, if you have such a greenhouse. Choosing an electric greenhouse heater that has automatic shutoff characteristics in case the motor overheats is essential. Having an electric heater that shuts off if it’s knocked over or is pushed against is essential if you live in a rural region where animals wander into your greenhouse. It’s crucial to have advanced thermal cut-off mechanisms in place for your safety.

Can a Greenhouse Get Too Hot?

“Yes!” is the unambiguous response to this query. You run the risk of essentially roasting your plants when the south and west sides of a greenhouse are exposed to direct sunshine. This is why every greenhouse (and even the smallest cold frame) has openings at the bottom and top to enable hot air to escape. Even if the calendar says it’s winter, your greenhouse might still get too hot if it’s sunny outside. When temperatures change, large commercial greenhouses utilize computerized controls to open and close vents, but if you run a tiny greenhouse, you’ll have to do the checking yourself. To avoid overheating your plants and flowers, especially in conditions like California’s, you may want to consider installing an electric fan even in the dead of winter.

Greenhouses Provide an Alternative Year-Round Environment

If you have a backyard greenhouse, you may create a cooler, more humid microclimate for your thirsty plants by gardening inside during the dry summer days. Using a misting fan and a shade cloth will help keep the greenhouse cooler, while a misting system will keep the humidity levels high enough for tropical plants to thrive.

You don’t have to give up on your garden when the weather gets colder. Fresh flowers, greenery, and fruit may be yours year-round thanks to a solar-focused greenhouse design and energy-efficient supplemental heating.

Sun and Insulation

Because the sun is a free source of heat, using the sun and insulation is an easy way to keep your home warm. This might be a challenge, but not insurmountable, when it comes to getting the most out of your solar power in the winter months. When compared to the height of summer, the length of daylight hours and the strength of the sun’s rays are diminished.

7 Tricks for Keeping the Greenhouse Warm Without Using Electricity - One Green Planet

Make sure your greenhouse is positioned in a location that isn’t shady in order to maximize the quantity of heat it receives from the sun. In addition, make sure your greenhouse is well insulated.

To get the most sunshine into your greenhouse, you’ll want to locate it in areas that aren’t heavily shadowed. When insulating your greenhouse, utilize semi-opaque or opaque materials like as aluminum or translucent plastic. Regular bubble wrap can be used instead of horticultural plastics for greenhouse insulation.

Using thermal mass to heat a greenhouse

The utilization of thermal mass in a greenhouse allows you to retain heat generated by the sun, a heater, or any other source.

Heat-absorbing devices can be placed in your greenhouse as thermal mass. When the temperature drops, the heat from those objects will be released.

A few degrees of extra heat can make a tremendous difference for your plants in your greenhouse.

In order to keep your greenhouse from freezing at night, you’ll need thermal mass.

Objects and materials with a high heat capacity are the best candidates for thermal mass. In this manner, the mass can store more heat throughout the day and release it at night when the air temperature decreases to release the heat.

There are a number of simple ways to add thermal mass to your greenhouse, such as:

  • Soil
  • Buckets of water (to maximize heat absorption, paint the buckets black)
  • Sand, gravel, or stones in a dark color
  • Porcelain ware
  • Blocks of concrete
  • For use as paving stones or bricks

These items retain more heat than the air does. So, make sure to place them in the most direct sunlight possible.

Make sure to place any plants that are particularly sensitive to heat near the thermal mass. The sun’s heat is absorbed more efficiently by items that are darker in color. In other words, whether you’re going the stone or pottery path, go with the darker one.

The chart below shows the heat capacity of several items compared to air, which might help you choose the best thermal mass for your project.

Thermal mass of various greenhouse materials

The heat capacity of water is shown in the graphic to be more than four times that of air. So, water is the best option for thermal mass, but the other materials are beneficial and can absorb some heat. Even if you could, a greenhouse would be impossible to construct entirely out of water.

Compost to heat a greenhouse

Compost does more than only absorb heat; it also produces heat.

Compost can be a pile of organic debris that decomposes to produce rich soil for your future plants that is rich in nutrients. For the time being, we won’t dive into the chemistry of compost breakdown.

In a nutshell, compost decomposes organic matter into soil, which generates heat.

As well as warming your greenhouse, compost supplies you with nutrient-rich soil for your spring plantings.

It is best to place the compost heater in the middle of the greenhouse if you intend to use it for heating. As a result, the greenhouse’s interior will be warmer and the heat will radiate forth.

Compost has the disadvantage of being unsuitable for use in indoor greenhouses due to its ability to attract mice and generate unpleasant odors.

Using a thermometer

In order to keep track of the temperature in your greenhouse, you’ll need a thermometer if you don’t already have one.

You can keep track of your greenhouse’s highest and lowest temperatures, and then compare those values to what your plants require. You’ll be able to examine how well the greenhouse’s heating system works and how warm it becomes. Your greenhouse’s insulation will be evaluated, and if necessary, changes will be made to the structure to accommodate the desired temperature change.


The greenhouse must be ventilated, even if the plants are insulated, in order to prevent any disease from spreading to the plants. Fans or holes in the ventilation can be used to allow air to flow. Open the holes in the morning so that some air may go in throughout the night when it’s the coldest. Make sure to seal all the holes before the sun sets in order to retain some of the heat.

Recommended plants

Winter is a tough time for many plants, but not all of them will be successful. If you don’t have a lot of money and time to invest in your greenhouse, some plants will suffer.

However, gardening can still be done even in the dead of winter. The key to having a greenhouse that is productive throughout the year is choosing plants that are cold-tolerant or require less sunshine.

In frigid climates, a decent greenhouse can sustain a temperature of 50 degrees Fahrenheit, despite the fact that you might assume otherwise.

Temperatures in this range are suitable for a wide range of plants, including several vegetables.

Even after a frost, some plants thrive even more (i.e. parsnips and brussel sprouts). If temperatures begin to fall, don’t let that discourage you.

It’s a good rule of thumb to look at a plant’s native climate to see if it can thrive in a cold or winter greenhouse. Potatoes, for example, can survive the winter in a greenhouse since they grow in colder climes (e.g. northern Europe, high elevations in South America). A greenhouse in Minnesota isn’t the best place to produce oranges because of their preference for warmer temperatures, such as the Mediterranean region.

Cold-climate veggies that can thrive include:

  • Broccoli
  • swiss chard
  • Kale
  • Onions
  • Garlic
  • Carrots
  • Beets
  • Potatoes
  • Strawberries
  • Cabbage
  • Turnips

Flora suitable for cooler climates includes:

  • Amaryllis
  • Azaleas
  • Pansies
  • Cactus decorated for the holidays
  • Larkspur

Outdoor versus indoor greenhouses

Both indoor and outdoor greenhouses have their advantages and disadvantages.

If you have an outside greenhouse, you’ll be able to grow a lot more food. However, they are more susceptible to freezing and the damage that results from frost. Maintaining heat will necessitate experimenting with thermal mass as well as having excellent insulation throughout the greenhouse.

Because they are smaller and easier to heat, indoor greenhouses are more common. Use your home’s existing heat source and supplement it with additional insulation to create an indoor greenhouse. Tomatoes and peppers, which require a higher level of heat, can be planted in this manner. There’s a lot of work involved in selecting spots that get the most sun. Direct sunlight is best received close to a clear window.

Related questions

Do greenhouses need to be heated in the winter?

Yes. Despite the fact that certain plants are able to endure the harsh winter, the vast majority of plants require heat in order to grow and thrive.

What temperature do you cover plants?

When the temperature drops below freezing, your plants are at risk of death from frost. Cover your plants if the forecast calls for temperatures to fall below 32 degrees Fahrenheit.

Can you plant plants year round in a greenhouse?

Yes. When given the correct conditions, some plants can produce flowers and vegetables all year long. If you buy a plant, you may be able to find out when it is best to plant it and what kind of climate it needs.

Final Thoughts on How to Heat a Hobby Greenhouse for Free

During the winter, the cost of heating a greenhouse might be prohibitive. Freely heating your greenhouse might save a lot of money in the long run. Even if it’s cold outside, you can keep your plants warm by using compost, thermal mass, and the sun.