Practical Tips: How to Heat a Greenhouse for Free?

Utilize passive solar energy by collecting sunlight during the day and retaining heat with thermal mass, like water barrels or stone, which release heat slowly overnight.

Building a greenhouse is one of the most effective ways to ensure the plants, flowers, and veggies are completely safe from freezing winter nights. Nevertheless, it still needs a heating system to warm the greenhouse.

The most popular way to heat your greenhouse over winter is to install a greenhouse heater. Despite being one of the most effective heating methods, it’s not pricey. So, how to heat a greenhouse for free?

how to heat a greenhouse for free
How to Heat a Greenhouse for Free?

The cheapest way to heat for free is to use natural sources like sunlight to raise the temperature inside your greenhouse. Some also ensure proper air circulation to build up warm conditions from the surroundings.

You can also try thermal mass to set up a greenhouse heating system.

Interested to know more? Find out further details about how to heat a greenhouse for free below!

Key Takeaways

  • Let sunlight in during the day.
  • Use water barrels or bricks to store and release heat.
  • Wrap the greenhouse in bubble wrap for insulation.
  • Place a compost bin inside to generate warmth.
  • Grow plants that do well in cooler temperatures.

What is a Greenhouse?

Before discussing further tips on how to heat a greenhouse for free, you better know the idea of the greenhouse itself.

The greenhouse was first built by a French botanist, Charles Lucien Bonaparte, in the 1800s to grow medicinal and tropical plants in Leiden, the Netherlands.

So, what’s a greenhouse? Well, a greenhouse is a sturdy structure made of fiberglass, plastic, or glass to cultivate crops, vegetables, flowers, and plants in a protected area.

how to heat a greenhouse for free

One of the main goals of a greenhouse is to protect the environmental conditions for growing plants from frost or excessive heat. This structure is also useful for extending the growing and harvest seasons.

Thus, you can pick your fruits and veggies despite freezing temperatures.

To maintain the temperature inside the greenhouse, you must install heat insulation. Generally, people will create an electric heater to heat up the soil. However, it will raise your electric bills.

For that reason, we are here to help you find the best way to heat a greenhouse in winter for free. Keep scrolling to the following sections to find out more about the methods.

Four Main Type of Greenhouse

You’ve probably seen many types of greenhouse structures. Starting from the shape of a house, attached to the wall, to the hoop ones.

However, there are some of the most popular greenhouse structures that people often build to plant their crops or flowers.

How To Heat A Greenhouse for Free
Small Greenhouse in the Garden

Here are the four main types of greenhouses based on the structures you can try building:

1. Lean-on Greenhouse

As the name implies, this type of greenhouse has a structure that attaches to the walls or buildings around it. Thus, it is popular as an attached greenhouse.

Considering its small design, you can quickly assemble it and place it between two buildings.

Then, set up a plant rack where you can grow your plants.

You will also have covers to cover structures and protect your crops from outside temperatures and pests. The advantages of this structure are that it is easy to assemble, inexpensive due to its small size, and has better access to electricity and water.

Also, you can make it as a fun diy greenhouse, thanks to the frame. However, you will have limited space to grow as many veggies as you want.

2. Even Span Greenhouse

We can say that it is the most common greenhouse you can find everywhere. It has an equal structure, where the roof bears the same length, angle, and width.

The shape is similar to a tiny house with a triangular roof.

Compared to other types, it has a flexible design.

You can build a spacious greenhouse in your backyard, thus allowing you to grow more vegetables. And for those with narrow spaces, even span greenhouses can be assembled into a smaller one.

Moreover, its glass material provides adequate sunlight exposure, which is necessary for plant growth and photosynthesis.

Unfortunately, due to its spacious layout, you may need help with the heating system. Also, the assembly costs are more expensive than lean-one greenhouses.

3. Uneven Span Greenhouse

Contrary to the previous type, an uneven span greenhouse has a rooftop with different slopes. One side will be much longer than the other.

Though it may look strange, this structure benefits those with greenhouses in hilly areas. It allows more sun exposure to pass through the greenhouse walls.

To get such a light condition, you can set the longer side in the south-facing area to get the most sun.

In addition to optimizing sunlight, the slope protects the plants from strong winds. Sadly, it only fits mountains or hilly regions.

4. Ridge and Furrow Greenhouse

Another simple and affordable greenhouse you can have in your backyard. It has an A-frame with covers on all sides, making it easy for you to insulate the heat.

You can easily build a greenhouse with plastic film or wood. For a bigger one, you may try to create two or three structures. Then, remove the walls at the end to provide more space for growing plants. Such designs are commonly used in farming fields.

Furthermore, the advantage of the ridge and furrow greenhouse is the even distribution of heat. Apart from that, you can easily assemble it without needing professional help.

In addition, it is cheaper than other types of greenhouses. So, you can rely on it to have one in your garden.

The Benefits of a Greenhouse Farming

If you are a gardener or a farmer who lives in a country with four seasons, you will understand how tricky it is to grow veggies outdoors.

You have to deal with freezing temperatures that can harm the roots.

Low temperatures inhibit water and nutrient uptake due to the frozen soil. As a consequence, your plants will grow slowly and even tend to be stunted.

how to heat a greenhouse for free
Greenhouse in a Farm

But thankfully, you won’t have this kind of problem anymore if you grow your plants in a greenhouse. It will protect your crops from harsh winters due to the hot air heating system. Also, it helps you manage the temperature quickly.

The greenhouse also ensures that wild animals, such as rabbits, weasels, or deer, cannot access the planting area. Thanks to the covers, this farming method also makes it easier for you to control pests and diseases.

Another advantage of greenhouse farming is that it extends the growing period of your plants. Greenhouses generally utilize thermal energy from heating systems, with or without electricity, to maintain stable temperatures favorable for the crops.

Such conditions promote vigorous growth. Thus, they can grow longer and produce bountiful harvests that benefit farmers.

Since you can adjust and keep the warm conditions, gardening will be more fun because you can add to the types of vegetables, fruits, or flowers planted in this area.

Nonetheless, some people against greenhouses argue that the structure makes it difficult for plants, especially flowers, to pollinate. It makes sense since it’s difficult for pollinators to enter the area.

But don’t worry! You can help pollinate manually with cotton rub.

What Temperature is Too Cold for a Greenhouse?

A cold greenhouse is commonly caused by the location where he lives. If you live in the northern hemisphere, it becomes natural that you will experience trouble heating a greenhouse.

Not to mention the duration of daylight is much shorter, reducing your plants’ chances of absorbing the sun exposure they need.

Also, your greenhouse will only have a short time to gather sunlight to warm up the site. Moreover, the winter in cold climates is usually more challenging and extended.

Most of the winter will also be accompanied by clouds and snow that make your greenhouse suffer.

Temperature in The Greenhouse
Temperature in The Greenhouse

In general, daylight temperature in the greenhouse should be around 75°F – 85°F and 60°F – 76°F at night in the summer. However, these temperatures will drastically drop in the winter, reaching around 65°F – 70°F and 45°F at noon and evening, respectively.

Once the temperature in your greenhouse falls below the minimum, you should immediately check the heating system to keep your plants frost-free.

Cold conditions can be detrimental to your plants, especially if you grow tropical. Most of them can only handle temperatures around 50°F. Otherwise, they will go dormant.

In addition, several greens, like spinach and Swiss Chard, cannot survive a hard frost. So, transmitting heat to the greenhouse is necessary to keep your crops thriving during the cold season.

Some people will install a heater as a quick fix to warm up the soil. However, it is not a great way to save money. Therefore, we would love to share tips on how to heat a greenhouse for free.

Check out the information in the next section!

How to Heat a Greenhouse for Free?

Heating a greenhouse with a heater is easy and efficient. However, having a self-heating greenhouse with free energy, like the sun, is more sustainable. Besides, it won’t rob your pocket to pay for electric bills.

Seems a real deal, doesn’t it?

How To Heat A Greenhouse for Free
How to Heat a Greenhouse for Free?

Let’s find out what’s the cheapest method to heat your greenhouse below!

1. Cheapest Way To Heat A Greenhouse

As we previously mentioned, using natural sources is the best and cheapest way to heat your greenhouse for free. If you are new to working with a greenhouse, we highly recommend incorporating plastic covers and sunlight.

You can use transparent plastic to wrap the sides of your greenhouse to optimize sun exposure that your plants can capture. Also, remember to build a greenhouse in a south-facing spot in your garden or backyard since it is the place that gets the brightest exposure.

Apart from these methods, our experts also recommend putting some thermal mass to collect the heat from the sun. It also works great for small greenhouse heating systems whose rooms are not spacious.

Thus can optimally warm the room.

The working principle of the thermal mass is to absorb the sun’s heat when it is hot, providing a cooling effect in daylight. Then, they release the heat to warm the planting site when the temperatures fall at night.

You can place water barrels as water can store heat four times better than soil and twice better than concrete. These materials work as a passive heating system that you can rely on without much checking.

2. How Do You Heat a Greenhouse with a Water Bottle?

Little did you know that water is an excellent heat absorbent. It can absorb heat and release a cooling effect during the day. In contrast, it turns up the temperature when the atmosphere is cold.

Hence, you can include water in your greenhouse plans. How to do it?

  • Find plastic water bottles to fill in with water. Don’t use glass, as it breaks easily during frost.
  • Using a paintbrush, paint a half side with black enamel color. Then, do it for the rest with a white one. Black color absorbs the heat, while white prevents heat transmission. So, the heat will be safely preserved in the water.
  • Prepare a saturated solution of salt and water. Make sure no more salt can be dissolved in the water to indicate the mixture is well-mixed. Salt can increase the boiling point of water, which, consequently, raises the heat.
  • Arrange the bottles in the north area with the black-painted sides facing the sun to allow maximum absorption of sunlight exposure. Instead of placing them in rows, it will be better to stack the bottles to optimize the heat collection.

3. How Do You Heat a Small Greenhouse Overnight?

There is no doubt that installing a heater is the most effective way to make the greenhouse warm through the night. It’s not a problem if you have an extra budget to have one.

On the other hand, it is not an ideal solution for those with limited funds.

Fortunately, you can still protect your crops from freezing temperatures by installing thermal curtains. They are made of thick fabrics to insulate heat in the structure.

You can also grow lights that generate heat and illuminate the area at night.

In addition, arranging water bottles to stack in the greenhouse is a brilliant idea to get heat for free.

Final Thought

Heating a greenhouse can be tricky during the winter months. Apart from having to deal with low temperatures that can damage your crops, you will spend a lot of money because you use a greenhouse heater.

Luckily, there are several methods you can try to heat up the greenhouse for free! One popular way is using plastic wraps to catch the sunlight, filling water bottles as thermal masses, and installing thermal curtains to insulate heat.

If you have to use a heater, replace it with grow lights as they need lower power. Thus, it will not consume much energy.

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FAQs (Frequently Asked Questions)

What should you not put in a greenhouse?

While most plants you grow in the garden are doing fine, thriving on typical garden soil, you will get into trouble if you put the soil in your greenhouse. The garden soil generally has the characteristic that it won’t let water escape easily.

Consequently, it can be very damaging to the roots as the constant damp soil will lead to root rot. Besides, such soil is usually too compact, not allowing good air circulation that the roots need to breathe.

In addition, it will intensely make your plant containers heavier. Thus, they will be tricky to move.

Why is your greenhouse colder than outside?

Your greenhouse is supposed to be warmer than the surroundings. However, if you notice the temperature goes lower, you should check whether there is an air leak around the area.

Or, the greenhouse location is in the southern area of your house, where the sun shines more intensely than in other parts. For that reason, you need additional equipment or materials to raise the temperature.

People usually install an electric water heater to make the greenhouse warm. But it costs you a lot of pennies! It would be better to replace it with hotbeds made of compost.

Besides being cheap, you can also use compost for plants. What’s a win-win solution, isn’t it?

Can solar panels heat a greenhouse?

Instead of using electric heating for your greenhouse, taking advantage of natural resources is way more sustainable, like solar panels. It uses solar radiation to be collected in the panel.

After that, you can use it to heat up the area.

To set up a solar panel, you will need batteries, a solar charger, PV solar panels, a heater, and an inverter. In contrast, heating a greenhouse with solar panels may cost you extra money.

But it will be worth it since this setting can last for up to 20 years if you properly care for it.

Can plants survive in unheated greenhouse?

Some may think it impossible to grow plants or vegetables in an unheated greenhouse. Surprisingly, you can grow greens without problems in winter! Some green vegetables like spinach and lettuce can succeed in this area.

Cool-season vegetables, like Brussels sprouts, celery, peas, cabbage, and broccoli, can also thrive in this greenhouse. Nonetheless, it is always better to provide extra protection.

Wrap the pots with bubble wraps or horticultural fleece about two screens to help sustain the heat.

The materials also prevent clay pots from cracking due to low temperatures.

Does a greenhouse stay warm at night?

Generally, the ideal temperature for greenhouses during the day is 75°F – 85°F, while the temperature drops to around 60°F – 76°F at night during summer.

In contrast, daylight temperature in the winter is similar to even a summer day, which is approximately 65°F – 70°F.

Meanwhile, the temperature in your greenhouses at night can get down to 45°F. So, it is normal to worry about your winter greenhouse. However, you can keep it warm by covering your greenhouse with bubble wrap and ensuring proper ventilation.

Some people also heat the greenhouse by adding compost as it generates heat naturally. The heater would be the best quick fix, but it will rob your pocket money.

Will growing light keep the greenhouse warm?

Besides installing ventilation to ensure good air circulation, you can use grow lights to raise the temperature in your greenhouse. The light generated from the LED bulbs will turn into heat, which your plants can use to stay warm during the night.

The heat generated is constant, thus preventing chilling damage to your plants in the winter.

Instead of installing a heater, it can be the most cost effective way to cut your budget.

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