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How To Heat Greenhouses In Winter

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Are you that gardener who is always reluctant to store away your gloves and trowel come winter? Or better yet, do autumn’s chilly days and nights get you mulling over what to plant come spring? Learning to heat greenhouses in winter will keep you on the path if this is the case.

A plethora of greenhouse heating options might make building one in your backyard a justifiable prospect.  See, you can never put a price tag on the feeling of satisfaction you’ll garner whenever you bring flowers and fresh veggies to your table in sub-zero weather. Besides, you need not necessarily indulge yourself in a high-priced project.

For every gardener looking to maximize efficiencies, even when cooler temperatures spark slower growth, you might want to read on for insight into the easy and affordable greenhouse heating techniques and heat retention tips. But let’s first have a quick introduction to greenhouses.

Overview

Each of our world’s climate zones is set apart by native plants that adapt to the local day span and air temperature ranges. That said, a greenhouse is a man-made ingenuity to create a micro-climate that is disparate from the outdoors, enabling a gardener residing in a locality with cold winters to grow delicate plants natively adapted to a warmer region.

Picture of tomatoes growing in commercial greenhouse

With a greenhouse, you’re bringing bits of the tropics into your backyard. Once you grasp the basic principles of greenhouse heat retention and their airflow and lighting management, your gardening prospects are practically infinite.

What is a Greenhouse?

It’s an enclosed environment that constitutes partial translucent material constructs. Greenhouse walls made of glass or plastic constructs tolerate the permeation by the sun’s electromagnetic rays into the structure to raise air temperature while retaining this warm air.

Brief History of Greenhouses

Since the invention of translucent materials, people have been relentlessly seeking more and more ways of using them to help grow delicate plants. The first recording of heating greenhouses was in Korea – dating back to the 1400s.

The cold Korean climate drove the populace to find ingenious ways to supplement the sun’s heat to open up more gardening possibilities.

Greenhouse heating in winter

The comprehension of winter greenhouse technology improved through the centuries until farmers could accurately control the humidity, temperature, and chemical constitution of the greenhouse atmosphere.

Today, the global agricultural industry relies on contemporary greenhouse heating systems; these first-rate upfront investments have automated digital controls with carefully regulated air circulations for guaranteed dividends during harvest time.

Advantages of a Greenhouse

The food demand in the vast European region relies greatly on greenhouse technology. Huge greenhouse complexes make it possible for fresh veggies and flowers to be flown worldwide. On the flip side, here are some of the basic benefits that you’ll get as a home gardener when you have access to a greenhouse in winter:

Extended Growing Season for Native Plants

If short cool summers typify your current locality, it can be difficult to watch your homegrown tomatoes ripen. Fortunately, a greenhouse lets you start seedlings when it’s still frosting outdoors.

Later on, the hoop house will also protect your delicate plants from becoming ‘mildewy’ over the drizzly summer days. Your greenhouse will allow you to keep harvesting ripe red tomatoes after the winter days have blackened the outdoor vines.

Wide-ranging Variety of Plants to Grow

Most veggie gardeners residing in northern regions find it challenging to ripen warm-weather crops such as eggplants and melons. What’s more? Growing citrus trees in regions with cold winters are pretty much out of the question.

Luckily, it might interest you that you can have them flourish in containers in your greenhouse over the winter season. What of those who hold a unique botanical interest? You can grow summer flowers all year round. See, it doesn’t matter if you’re a herbalist or an orchid fancier; a greenhouse presents expansive opportunities for your floral repertoire.

Precipitation and Wind Protection

Nearly all gardeners have felt the pinch of having tender plants destroyed due to extreme precipitation. Case in point – downpours can bend your tulips to the ground, and a coat of snow can ruin a garden of your delicate spring flowers.

A greenhouse presents you with the opportunity to take charge of the surroundings. You can install an electric heating system or work with solar energy and variant heating sources to realize the desired growing conditions for your plants.

3 Ways to Keep Your Small Greenhouse Warm

  • Direct Solar Energy
  • The Sun as a Passive Heat Source
  • Electric Heaters
electric heater

Electric Heaters

parafin heater

Kerosene Heaters

Want to start small with a vision of supplying your family with garden-fresh, year-round greens? You might be delighted to know that there several modern energy-conscious greenhouse heating alternatives as there are greenhouses. So, why not kick it off by simply turning the individual beds in your garden into cold frames?

With such an ultra-simple greenhouse set-up, some glass windows or plastic sheets resting on top of the bed will protect your tender seedlings from a cold winter. You might want to ensure that these roofing constructs are built so they can be lifted when the sun gets awfully warm. Here are a couple of techniques you can use to heat such a greenhouse come winter:

Direct Solar Energy

Now… full disclosure – this might work. You can position your small greenhouse, so its north wall aligns with your home’s south end. This way, the greenhouse will be more of a south-facing extension of your house.

You might want to remember that this is an attempt to make the most of what little sun you have to garner some solar-generated warmth. Plus, it will help keep your home’s heating bills low because it creates a heat sink for your house.

The Sun as a Passive Heat Source

The chief and most vital heat source for any glass or plastic greenhouse is solar energy, the direct sun rays that infiltrate through the walls of your greenhouse. The sun’s electromagnetic radiation will warm up all of the objects you have in your hobby-sized greenhouse, including any thermal mass there.

A good example of a thermal mass to use is a huge black-painted 55-gallon barrel filled with water (or whatever is conveniently available). You should strategically position the thermal mass in your greenhouse to create a heat sink that’ll absorb energy during the daylight hours to give it up slowly in the cold dark.

Using bubble wrap during winter as an insulation technique for the translucent walls of your greenhouse is yet another way to maximize the use of the captured warm air. You probably have bundles of this greenhouse insulation commonly lying around in your home – the inexpensive material from mail-order parcels.

Electric Heaters

These are probably the most popular ways to keep a winter greenhouse warm overnight. They are safe and don’t populate the atmosphere of your greenhouse with emissions as compared to their paraffin and propane counterpart systems. Fan heaters reduce the possibility of cold spots developing in your micro-climate setting through even warmth dispersal. 

The simplicity of an electric heater with an automatic timer or thermostat makes it easier for gardeners who have to be away from their greenhouse on workdays to grow delicate plants. All you have to do with this type of heating system is set the thermostat on the small-space heater and be on your way; it will only turn on when needed.

Moreover, today’s heaters have integrated safety features for reliability and convenience. For example, they have an automatic shut-off function in case they get too hot or tipped over. Making the most of the contemporary and ingenious greenhouse heater technology lets you approach your gardening endeavor with a real farmer’s savvy.

4 Tips to Heat Your Greenhouse for Free

When considering the variant greenhouse heating alternatives, you might consider it wise to consider the free options first. Once you make the stride to take advantage of all of the sustainable techniques to trap the warm air in your greenhouse, you can include an electric heater as a supplementary option for use when needed. Below are a couple of tips you might want to apply to keep your greenhouse warm for free:

Strategic Positioning of Your Greenhouse

As aforementioned, the best way to trap solar energy is to erect your greenhouse with its south end facing direct sunlight. You might want to remember that the winter sun in the northern hemisphere always is in the southern region of the sky.

Use a Thermal Mass to Store Warmth

Once you have your hobby-sized greenhouse strategically positioned – to capture all that available free winter sunlight – your next move ought to be finding the most sustainable ways to trap the warmth you gather.

In the section above, we discussed that one of the most common ways gardeners avoid unexpected temperature drops is by including an ideal thermal mass object in their greenhouses; they take up and hold a considerable amount of heat.

Another ingenious way to curb these abrupt temperature dips is to use insulating constructs, like cinder blocks, to erect the north end of your greenhouse – that doesn’t get direct sunlight. These cinder blocks will absorb warmth from the hot atmosphere in your greenhouse during daylight and slowly dissipate it overnight.

You might want to remember that, even on some cloudy days, heat sinks like stone walkways, huge volumes of water, concrete grow boxes, and so on will help condense heat loss during cold nights.

Proper Insulation Practices

Ever heard of the adage ‘did you grow up in a barn?’ Well, the same applies to a greenhouse. What do you do right after generating your hard-earned heat through the various ways we discussed above?

Your next step should be making every possible attempt to hold on to that warmth. To achieve this, you might want to survey your greenhouse for any gaps or cracks. Wherever you find either, smear silicone caulk to curb heat loss. Duct tape can also be a good alternative for a quick fix.

Even though a certain degree of air circulation is much needed in your greenhouse, you should keep the airflow in check through deliberate openings or vents. Remember, your aim isn’t to have it inadvertently leak out only to have cold patches in your greenhouse.  

As aforementioned, bubble wrap is a good insulation option for greenhouse walls made of clear glass or when you aim to double up plastic sheeting. You might want to know that the air in the bubbles has impeccable insulation properties, just like your puffy down parka is great for your body’s insulation.

What’s more? Adding horticultural fleece over your delicate plants as row covers is another good insulation approach. You might want to remember to remove the layer of fleece during daylight to ensure that the plants get enough ventilation and light.

Passive Heat Sources May be Enough

The greenhouse heat retention techniques we reviewed in the sections above can be amazingly effective. You might not have to include tangible heat sources if you reside in a fairly temperate climate.

Just a couple of full water barrels and bubble wrap insulation use may be enough to protect your delicate plants if your locality doesn’t experience sub-zero conditions. If anything, you might even have to let the warm air out by opening the vents.

blue plastic barrel
Bluewater Barrels used as passive heating. Available from Amazon

Cheap Techniques to Heat Your Greenhouse

In today’s high-cost fuel age with a budding desire to garden a whole lot more sustainably, the attention of most gardeners concentrates on operating their greenhouses with the least possible cost in contrast to energy usage. Let’s review some of the cheap heating techniques that best suit modest greenhouses rather than commercial spaces:

How to make a 100 Hour Candle.

Compost Pile Use

Compost is undeniably a gardener’s best friend. Here’s the key twist: finding the desirable blend for your crops might take years to perfect. Nevertheless, there’s another beneficial use to compost beyond feeding your plants with essential nutrients: heat!

If you’re that serious enough grower considering erecting a small greenhouse, you surely already are composting kitchen waste and other organic material. The chemical decomposition that occurs in compost dissipates energy from heat.

Cornell University plans are underway to help farmers in the commercial sector adopt compost as a major source of heat for barns and huge greenhouses. In your case, a fairly casual compost pile can benefit your heat-starved plants during the winter season. A compost pile of merely 10 gallons (two large plastic buckets when full) can dissipate heat, rising well over 120 degrees Fahrenheit.

What if I am concerned about bringing contaminants into my greenhouse? You might be delighted to know that weed seeds, fly larvae, and thermo-sensitive pathogens should all die out at temperatures exceeding 104 degrees. You should remember that their initial thermophilic phase can last for weeks or months.

Therefore, you might want to turn your compost pile at least once a day for a few days to ensure that the cooler peripheral sections of the compost get to be at the center of the pile for some time. Your compost pile will dissipate heat to the surroundings through convection, conduction, and radiation.

Also, you can expect the moisture from your properly wetted compost to contribute valuable humidity to the humidity of your greenhouse. To understand the composting process better, check out this post called: Composting For Beginners The Complete Guide

Combustion

Considering the various winter greenhouse heating alternatives, it’s difficult to look past the fuel-burning ones. Even so, you ought to remember that when you use any of these combustion options, you will have to deal with carbon monoxide. That said, you might have to seek out construction experts to erect a safe chimney or vent. Let’s have a look at some of the fuel-burning greenhouse heating options for you:

Gas Heater

Unless you have to convert your house’s sun porch to integrate your home with the greenhouse, it’s highly unlikely that your utility company will grant you access to their natural gas supply.

Nevertheless, you can always purchase propane tanks to hook them up to your greenhouse’s propane heater. The key takeaway from using propane as a heat source is that you need a sufficient supply of oxygen for it to burn properly and safe ventilation for the expelled gases.

Check Current Amazon Prices Here.
Butane heaters are fantastic for larger greenhouses. Check out current prices on Amazon

Wood Stove

This is a greenhouse heating alternative that doesn’t rely on fossil fuels. If you have easy access to firewood, this might be a sustainable way to heat your greenhouse occasionally.

Then again, they might not be your best greenhouse heating option if you reside in a locality with cold winters because they’re labor-intensive; you not only have to procure and haul the firewood, but you also will have to tend the fire to keep the flame alive. What’s more? You’ll have to ensure that your greenhouse’s chimney is insulated properly because it can get extremely hot.

Rocket Mass Heater

Most homesteaders who design huge greenhouses as a bridge to a sustainable way to live are impressed with the rocket mass heater as an energy-efficient heat source. A high-temperature combustion compartment is infused into the architectural design of a building; the wood-burning chamber is integral to this particular masonry mass.

Combustion gases make their way through the masonry, consequently heating up the thermal mass, which radiates the heat outwards for hours.

Paraffin or Kerosene Heater

With these heaters, you have to light a wick that draws the liquid fuel from its holding tank. Luckily, they’re strapped with some safety feature that extinguishes the heater in case it’s tipped over. That said, it might be unwise to look past the fact that they still pose a noteworthy fire risk.

Because these heaters dissipate air pollutants like nitrogen oxides, sulfur dioxides, carbon monoxides, and polycyclic aromatic hydrocarbons, you might want to ensure sufficient air circulation in your greenhouse.

Check Current Prices On Amazon
Kerosene is fantastic heaters for small greenhouses

3 Energy-Efficient Tips to Keep Your Winter Greenhouse Warm

The ideal greenhouse heating system for you will surely be responsive to in-the-moment temperature requirements. Growing delicate green gold in your greenhouse year-round implies that you’ll only need the heat occasionally.

You’ll find that passive solar energy, a warm compost pile, and bubble wrap insulation often present sufficient warmth for your backyard greenhouse. When you protect your tender plants from the chilliest of nights, you can look to the electric heater as a reliable and energy-efficient solution.

No Need for Winter-Time Ventilation

In sub-freezing weather conditions, using a gas heater to heat up an indoor setting like a greenhouse is somewhat counterproductive. Why? Your greenhouse will need venting.

Such outdoor heat solutions are perfect for open-air settings like campsites. Then again, they’re less practical when you intend to create an indoor micro-climate. You might be better off opting for affordable electric fan heaters. Some of these come with sensitive thermostats to ensure they only run if the temperature dips below a specified point.

Fan Heaters for Healthy Air Flow

Each greenhouse gardener faces the challenge of air circulation. Overly still air in your backyard will encourage mildew and mold growth. How? The moisture in your greenhouse atmosphere collects on the foliage and other surfaces and fails to evaporate easily in the humid surrounding – especially if there’s no breeze.

So, how do you solve the issue? In the warmer seasons, you have to open up the vents on the roof to release the warm air and draw in cooler air through the vents that are close to the floor. However, during cold winters, you ought to have all the vents tightly closed up to trap the much-needed warmth inside. This is when molds can be a major issue.

Therefore, an electric fan heater is the best option to guarantee healthy airflow in your setting, even in the coldest of winters.

You should place the electric fan heater in an open and pivotal spot in the greenhouse, away from water. Plus, it’s wise to angle its airflow projection to be above the close plants; this way, you’ll avoid the desiccation of foliage by the warm air from the heater.

Safe Greenhouse Heating Practices

If you own a backyard greenhouse, you must be confident that whatever heat source you rely on is completely safe. You might find it wise to opt for an electric greenhouse heater strapped with automatic shutoff features in case its engine overheats.

If your area of residence is rural, you are at risk of having animals make their way into your greenhouse. You need the assurance that your electric heater will turn off if it’s tipped over or an object is pushed against it. So, the ingenuity behind these advanced thermal cut-off systems is vital for your peace of mind.

Problems

No matter how carefully you water your delicate plants, dampness, associated molds, and rots can be challenging. Therefore, you ought to ensure that you shed off the surplus moisture in your greenhouse on sunny days. You might have to use some heat to dry out your backyard setting to avoid losing your plants.

You have to ensure that some of the crops – for example, alpines and winter lettuce – get as much light as they possibly can during winter because they’ll suffer if your greenhouse’s insulation casts too shade on them. You might find it wise to avoid using materials like bubble wrap for plants that are quite hardy enough to outlive the winter season.

Conclusion

All things considered, a greenhouse is a wonderful setting for any garden enthusiast; especially in the spring season when your benches are full of gleaming green starts, and also in the summer when you prop open the roof vents and door with your nurtured cucumbers sprawling from the ceiling, and your tomato fruits ready to be picked.

How about the coming winter? Not quite as much. This is when your potted plants and the overwintering herbs agree to cluster together. You have a couple of brown, leafless vines hanging from the overhead trellis – with several planted seeds yet to sprout too.

As we’ve discussed, keeping your hobby-sized greenhouse warm and well-ventilated is vital to seeing your tender plants overcome a harsh winter. Hopefully, this guide has persuaded you not to abandon your garden when winter approaches.

This winter, you might need a solar-focused backyard greenhouse build and a safe, energy-efficient heating alternative to growing sustainable green gold, fresh flowers, and fruits. 

I hope that this post has given you all the information you require, but if you want further clarification, then check out this post: The Insider Secrets On Greenhouse Heating