Greenhouses, by their very design, are excellent heaters in and of themselves...

The science of the greenhouse effect itself (which, obviously, took its name from the greenhouse) allows these plastic-covered structures to trap heat generated by the sun’s rays - creating ideal environments for growing plants, where they wouldn’t have been possible otherwise.

For thousands of years, this has been a genius way to protect sensitive plants during the coldest times of year, and even extend one’s seasons. In turn, it can boost possible yields, increase product availability at certain times of year, and even rev up one’s profits! Still, these structures can be limited in how much heat they can trap and maintain, especially the colder temperatures get.

After all, plastic has a very low R value (insulation potential). But it has to – plastic coverings must be thin and translucent enough to create the greenhouse effect in the first place. Unfortunately, this means that heat can eventually be lost through these thin membranes, especially the colder it gets outside and heat is drawn out and away. For the most professional, ambitious, and daring of greenhouse growers in the coldest of climates (or those in the business of year-round hot weather plant growing), you’re going to need a little help in the realm of heating capability!

Luckily for you, there are tons of heating options out there. Trying to master cold climes and work harmoniously with the natural fluctuations of the seasons to your benefit? Do you want to heat your structure in the most sustainable way you can, or even in the most cost-effective way possible? Regardless of what you’re after, here are some excellent heating options that you absolutely shouldn’t skip, and which can help you achieve any or all of the above.

NATURAL GAS HEATERS

Natural gas is a likely option you’ll find in the line of greenhouse heaters available out there. It uses burned natural methane to raise your structure’s internal temperatures a few degrees, helping it maintain the environment you need for your stock.

You can use direct natural gas heaters, though there are also gas-fired heaters very similar to what you’d find as part of the central heating furnace in your home. Some of these are quite energy efficient!

Some advantages to natural gas: it’s very clean burning. In fact, it off-puts carbon dioxide and even some water vapors, which in the long run are very beneficial to your plants. Because you’re not using electricity, accidental power outages will not affect your plants whatsoever. A definite plus! Keeping a uniform ambient temperature in your structure can be one of the biggest struggles for greenhouse growers. Especially in hoop or gothic arch shapes, heat generated can raise to the top and sit there, instead of remaining near floor level where all your plants that need the warmth happen to be.

Some heating models come with aluminum reflectors which help distribute heat from the greenhouse floor and up, keeping the air temperature the same throughout, no matter the height. You can also get excellent control of your inside temperatures with the use of a built-in thermostat.

On the other hand, you will have to install or construct a ventilation system to aid with the effects of off-gassing, and prevent them from being too trapped in your greenhouse and thus bringing harm. For those wanting to run an environmentally sustainable business too, these growers should know that the use of natural methane gas does contribute to greenhouse gases in the atmosphere, and can affect the environment.

PROPANE HEATERS

What makes a propane gas heater different than using a natural gas heater? On the plus side, propane is not labelled as a greenhouse gas. Though you will need to think about a ventilation system to prevent trapping of gasses inside, it won’t be bad for the environment or the planet.

Still, natural gas is persuasive in that it is cheaper and more cost effective than propane. Simply put, propane is a more expensive gas-type heater to invest in. Is propane more dangerous to use than natural gas? The answer is no – they’re actually both about the same.

Your choice between the two really comes down to how much you are able to spend, and the environmental impact you want to have. Do you want to run an environmentally sustainable business? Then propane may be better. If you need cheaper costs for your startup, on the other hand, then natural gas will be your best bet.

WOOD STOVES

This may be considered the ultimate sustainable, environmentally-friendly, and even cost-effective heating option all in one. The only hang up: you’ll have to be a rather resourceful grower to keep one of these running!

Getting a wood stove set up and installed to heat your greenhouse is quite a cinch, but that’s not the hard part. The real challenge will be sourcing all the wood you need to fire it up, which can be a lot of extra work: whether chopping down your own wood or buying it from a logger or other source.

It’s also much more difficult for growers to fine-tune and have complete control over the temperatures in their greenhouses with a wood stove. They require a lot more supervision to prevent temperatures from getting too hot, and the air too dry – though it is the perfect model for cost efficiency and sustainability in one.

ELECTRIC HEATERS

Electric heaters are a very simple, straightforward, and elegant option, especially for the busiest growers. Their unfortunate downside, however, is their enormous drain on power. Compared to other options, they certainly aren’t as cost effective – nor are they environmentally friendly if they run on the grid. If power outages ever do happen, you’re out of luck during cold times when your plants completely depend on the extra heat.

Further, electric heaters are notorious for their potential to dry the ambient air instead of moistening it, as is the case with gas heat sources. For that reason, using an electric heater may require you to keep a sharper eye on air moisture, and perhaps even invest in humidity controls for the welfare of certain plant species you might want to grow. Still, these can be an excellent choice for smaller greenhouses that don’t need as much circulating heat to function throughout colder times.


HOT WATER HEATERS

While hot water unit heaters (also called horizontal steam or hydronic unit heaters) are not the first option you might think of among the available heaters out there, nonetheless they number among the most efficient – and are quickly becoming the most popular. Hot water heaters are far superior to other methods in some big ways. They provide more uniform temperature changes throughout a space, so you won’t have issues with heat rising away from your plants and to the top of a greenhouse structure.

The warmer air produced by hydronic units is also clean and damp, instead of having a tendency to dry out or carry around impurities, like with other options. This makes it much more ideal for your plants and their health, too – which in the end leads to a better crop. Best of all, however, are the efficiency and cost benefits. These heaters require hardly any electricity or other power to work, and their upfront costs are sometimes much lower than other options.

Last but not least? They have some of the lowest environmental impacts out there, making it an excellent sustainable option. Grow in your greenhouse with a sound mind – and that’s priceless!

PASSIVE HEATING

Resourceful growers of all kinds have found ways to passively heat their greenhouses during cold weather. In other words, they create heat for their structures with as little power (and cost) as possible. Solar-powered passive heated greenhouses are one option. However, it does require some substantial up-front investment.

Similarly, radiant heating is becoming a popular and sustainable option. Akin to hydronic unit heaters, they instead use passively-heated water pipes to generate some heat while using minimal power. This method can be tied into either a solar or hydronic heating system. In addition to more complex systems though, there are some more affordable and more low-key, clever tricks that some greenhouse owners have gotten the hang of to give their structures just a little bit more heat.

Using the addition of fresh or hot compost – or moving your compost pile into and under your actual greenhouse structure, for example – can boost the inside temperature up by a degree or two if you really need it.

Others have used black barrels filled with water or even lined the floors of their buildings with black stones, which absorbs and re-radiates heat outward to keep the air above freezing. While some of these can elevate the temperatures of your greenhouse just a few degrees in a pinch, more sophisticated and powerful heating units may be needed for the coldest of regions: such as in the Midwest, Alaska, and any or all northern states.

In generally warm climates where winter doesn’t create drastically cold temperatures, however, some of these passive options can be real money savers and perfect solutions.

STAY WARM!

There are so many options to choose from for heating your greenhouse. Depending on what factors you find the most important – efficiency, costs, environmental impacts, or the welfare of your plants – you’re bound to find something that’s absolutely perfect for you and your growing needs, even during the coldest times of year, or in the coldest parts of the country.

Contributer: Adrian White

Adrian White is an organic farmer and gardener of 8 years, and a food, health, and agricultural writer of over 5 years. Now living in Iowa, she has administrated CSA’s as well as farm packing operations, fueled by a passion for being a young organic farming presence in an ag state that sorely needs a new generation of farmers.