Everyone wants to know the cheapest way they can heat a greenhouse over the colder Autumn and Winter months. There are quite a few common sense, cheap, easy and efficient ways which you can try and that should enable you to keep your greenhouse frost free and your plants protected from the Great British weather. The main objectives are basically:
- Keep the cold out
- Keep the heat in
- Increase the current temperature.
Keep The Cold Out
The first step is to check your greenhouse and make any necessary repairs. This should include:
Replacing or repairing broken glass or ripped polythene or plastic
Ideally you should replace broken panes of glass, polycarbonate or acrylic but if there is only minimal damage then you could carry out a cost-effective repair using our All Weather Tape.
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All Weather Tape When there is a small crack or split in your greenhouse glazing, by covering with this tape - ideally on both sides of the glass, polycarbonate or acrylic - will help to prevent further damage. Click here to see full details.
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This tape is also perfect for covering rips in polytunnel covers - again cover the rip on both sides and hopefully this should mean that you don't need to replace the whole cover and the rip won't become longer.
If the crack in the greenhouse glazing is too large to be repaired in this way or a piece has fallen out, then you will need to replace it. So it is now a case of deciding whether to replace glass with more glass or using a sheet of polycarbonate. If the appearance of the greenhouse is important to you then you will want the replacement to be the same material. However, if you are happy to have a repair that will be more obvious, then replacing the broken pane of glass with a piece of polycarbonate has many advantages.
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Advantages Using Polycarbonate
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If you need to replace a polytunnel cover then the first thing to check is whether you currently have a ‘fitted’ or ‘shaped’ cover (often found on smaller polytunnels) or whether it is a flat sheet of polythene which is shaped and tensioned by fixing it over the hoops of the structure.
For a replacement shaped cover it’s often best to go back to the supplier you purchased the polytunnel from to see if they offer replacement covers. If this is not possible, you will need to take good measurements and consider the shape of the structure – for example whether it has curved or straight eaves – before looking around for a new cover. A good example of a shaped cover is shown in the image below which shows the Gardman Grow It Polytunnel.
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The frame of this polytunnel is powder coated tubular steel so you could expect it to potentially last for up to 20 years. Over that length of time you will need a replacement cover so unless you can get an exact replacement from the original manufacturer then there will be lots of measurements to take to ensure a different cover would fit. Click here to see details of this cover.
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The other alternative would be to purchase a length of polythene to then drape over the structure and create your own cover. This definitely requires more DIY skills but would mean you did not have to purchase a whole new structure.
On larger polytunnels when the cover is damaged beyond repair then you will need to purchase the correct width and length of polythene to cover the frame.
Keep The Heat In
Just like your house, to heat a greenhouse economically it is important that you retain any heat generated – there is little point heating an area if the heat is then allowed to escape through open doors or windows – or simply through the fact that if your greenhouse is glazed with glass then glass allows heat to escape more readily than many other materials. However, we wouldn’t expect you to completely reglaze your greenhouse or not allow fresh air into it, so here are our tips on keeping the heat in your greenhouse for as long as possible.
Adding Insulation
Just like lagging a loft to prevent heat from escaping through the roof of your house, by insulating your greenhouse you can keep the heat where it should be – inside your greenhouse! Ideally you would apply insulation to any areas of your greenhouse which are glazed – as you are then preventing the heat from escaping through the glass.
The easiest and most efficient material to use to insulate your greenhouse is bubble wrap – just make sure that you purchase the type which has been specially designed for greenhouses, such as our Heatsheets, as unlike ordinary packaging bubble wrap, that designed for greenhouses will be UV stabilised so will last longer.
We are often asked whether small or big bubble bubble wrap is better. We prefer the small bubble version as it’s easier to fit and you shouldn’t see any difference in its insulation properties when compared to the larger bubble.
When fitting bubble wrap insulation to your greenhouse we recommend attaching it so the bubbles are facing the glass – bubble wrap will be in place for quite along time so putting the smoother side to the inside of the greenhouse means there are less places for dirt or moisture to get trapped and the surface is easy to wipe clean. Also, try to have as few joins as possible – you can either start at the base of the greenhouse, run the bubble wrap up the side of the greenhouse to the ridge then down the other side. Or you could start at the door, running the bubble wrap down the side, across the back, along the other side and back to the door. Where you have joins it’s best to overlap the bubble wrap and cover the joins with all-weather tape to ensure there are no gaps.
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For attaching bubble wrap to an aluminium greenhouse specially designed, reusable fixings are available. Suiting most makes of greenhouse these clips simply slot into the channel in the glazing bars. You then turn the clip to ‘lock’ them in place. |
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When you’re ready to remove your insulation simply turn to unlock and remove. These same clips can also be used to hold your shade netting in the summer months.
When fixing the bubble wrap in wooden greenhouses it’s trickier as although in the past you used to be able to purchase ‘woodpins’ to hold the insulation in place, these are no longer manufactured. The best alternative would be to use map pins or drawing pins – you just need to make sure that their spike is long enough to go through the insulation and then push into the wooden frame of your greenhouse.
Control Ventilation
To allow fresh air to continue to flow into your greenhouse through the colder months we suggest you use your louvre window rather than opening your roof windows or leaving your door open.
If you have automatic openers fitted to your roof windows you can prevent these from opening by either removing the cylinder from the Bayliss XL openers or removing the adjustment pin from the Bayliss MK7 models – just remember where you’ve put them when it comes time for removing the insulation and putting the window openers back into operation.
If you don’t have a louvre window in your greenhouse, then it is possible to add one by using a Louvre Kit.
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Essentially a louvre kit provides you with the right- and left-hand fitments which hold your glazing. What you must do is remove the glazing from the area where you want to fit the louvre and cut the glazing to form the blades of the louvre. The fitments are then attached onto the frame of your greenhouse, the blades fitted, joining the right- and left-hand fittings together. Click here to see full details.
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You can now adjust the louvre open slightly, to allow some air without allowing too much of the warmer air in the greenhouse to escape.
Increase The Temperature
So far you have repaired your greenhouse and insulated your greenhouse. If the temperature in the greenhouse is still too cold for your plants, then you need to add some heat. To heat a greenhouse cheaply you want to make sure you use the right product to generate the heat and that you don’t waste money heating areas which you don’t need to.
Make The Area To Heat Smaller
The smaller the space you need to heat the cheaper it will be. So if all the plants you are caring for in your greenhouse over winter can be kept close together, rather than spread all around the greenhouse, then you could ‘divide’ your greenhouse up and only heat the section where the plants are.
‘Dividing’ up your greenhouse might sound complicated but it’s actually quick, easy and cost effective in the long term. Basically you need to create a temporary ‘wall' or ‘curtain’ which can be done using the same material you have used to line your greenhouse.
Simply cut lengths of Heatsheets which you can fix to the roof of your greenhouse and that are long enough to fall to the greenhouse floor. By suspending a number of these lengths across the width of your greenhouse you will be able to successfully create a shorter area into which you can then add a source of heat.
When creating this ‘divide’ we recommend securing the top of the Heatsheets to the roof of the greenhouse using a strong double-sided tape.
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Rather than using a standard double-sided tape you could purchase from a craft shop, you need one which will not be affected by being used in a greenhouse environment such as our Double-Sided Tape. We’ve chosen this tape as it is perfect for use on uneven or difficult to bond surfaces and will not deteriorate when exposed to sunlight or moisture. |
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Provide Localised Heat
If you are concerned that to heat a greenhouse that you need to heat the whole space your plants are in then you could consider providing localised heat by using a warming pad or heated tray and standing your plant pots or seed trays on top of that. These tend to be low wattage, are available in a wide range of sizes and provide heat exactly where it is needed – at the base, so near the roots of your plants.
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A good example are the Warming Pads from Bio Green. These are available in three different sizes, from as little as 10 inch x 14 inch which is just 15 watts, up to their largest size which is 16 inch x 25 inch which is only 42 watts. Click here to see details of these pads.
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If you look closely at the photograph above, you will also see that Bio Green are providing you with another money saving hack. You can see that they have placed their Warming Pad on top of a piece of polystyrene. By doing this any heat generated by the Warming Pad is being forced upwards towards the plants and not being lost into the surface of the bench and below. Our Root!T Heat Mat and Insulation Kits take this potential loss of heat into account by including a mat designed to direct the heat upwards to your trays and pots.
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Root!T Heat Mat and Insulation Kits Designed to provide a uniform, gentle heat across their whole surface, these Heat Mats are available in three low wattage sizes:
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As a strong, robust alternative to these roll up heat mats here at Two Wests & Elliott we manufacture our aluminium Heated Trays.
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Heated Trays With a rust and rot proof aluminium outer these Heated Trays are virtually unbreakable. They also have built in insulation which directs the heat to the top of the tray, so no heat is wasted through the base of the tray. Click here to see details of these heated trays.
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Being aluminium also means that they can be used on uneven surfaces – for example on slatted staging as shown in the photograph above – without having to place anything below them.
Available in two sizes, these still have relatively low wattage, especially when compared to a heater, so are still economical to run. And, if you wanted to increase the temperature for your plants sitting on these trays we also offer sturdy covers which fit over the tray to trap the heat into an even smaller space.
Add An Economical Heater
If you can’t fit your plants onto a warming mat or heated tray as described above, if you have divided your greenhouse with a partition of insulation, then you should be able to use a smaller heater to keep the space frost free.
The lower the wattage of the heater, the less electricity it will use when running. Most electric fan heaters are described as having a kW rating – which stands for kilowatt, one kilowatt equals 1,000 watts. So when you're searching for a low wattage heater it’s best to look at the tubular heaters, where wattage can be as low as 28 watts per foot length.
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Our range of Slimline Eco Tubular Heaters are exactly as their name suggests – economical to run. They combine the features of a traditional tubular heater but have a built-in thermostat keeping energy usage to a minimum. Available in five lengths, the shortest at just 12inch has a rating of just 28 watts. |
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For a slightly more powerful, yet still low wattage tubular heater, take a look at these traditional Tubular Heaters which have a rating of 60 watts per foot length.
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Available in four sizes, ranging from 12inch / 60 watts up to 48inch / 240 watts, these traditional tubular heaters do not include a built-in thermostat but still provide a gentle, radiant heat. Click here to see details of these heaters. If you want to be able to set a temperature you want these heaters to turn off at then you would need to use a separate thermostat to control the heater. |
Tubular heaters are a good choice for using in a greenhouse environment as they are IP rated high enough to be used in damp conditions – the Slimline Eco Tubular Heaters have an IP44 rating making them resistant to sprinkled water from every direction, whilst the more traditional Tubular Heaters have a higher IP54 rating, so can be splashed with water without any damage.
Obviously, being low wattage heaters they are less powerful than fan heaters, so although they will cost less to run they would struggle to heat a large greenhouse which means they are more suitable when you have divided your greenhouse enabling you to heat a smaller area.
This blog post on how to heat a greenhouse cheaply has been created from our personal knowledge, information gathered by speaking to other gardeners or manufacturers in the gardening industry, by reading gardening magazines and devouring information from books and the internet. We aim to be as accurate as we can, so if you find a mistake, please remember, we’re only human.