Cheap and Cheerful Ways to Insulate Your Greenhouse

, written by gb flag

Frosty greenhouse

A greenhouse really makes a difference to what you can grow in cooler climates, and not just in summer. In winter it’s invaluable for keeping crops in good condition that would otherwise suffer outdoors. Not only does it keep plants a few degrees warmer, it also protects them from being battered by wind, rain and snow – invaluable for seedlings in spring.

Even if you’re growing crops outdoors over winter, it makes sense to bring on a few under cover too. For instance I’ve found that growing cabbages in my greenhouse over winter means they’re ready a couple of weeks before the outdoor ones in spring – plus they serve as insurance to offset any losses due to weather or pigeons.

If you’re worried that your unheated greenhouse is just too cold for your overwintering plants, here are a few cost-effective ways to make it extra snug.

Insulating Your Greenhouse

Before insulating your greenhouse, the first thing to do is block drafts. Replace any broken panes, seal gaps in the frame, and make sure that doors and vents fit securely.

Bubble wrap can be used to insulate greenhouses

Lining a greenhouse with an inner layer of plastic – essentially creating double glazing – will seal off air gaps and reduce the rate at which heat escapes. Good old bubble wrap is the greenhouse grower’s go-to cheap insulation material.

Bigger bubbles are better, as they allow more light in and provide better insulation. Purpose-made horticultural bubble wrap has large bubbles and is also UV-stabilized, so it should last longer than the stuff used to pack your latest online purchase. Having said that, if you’ve got a lot of that lying around why not save a few bucks and use it? When it degrades you can send it away for recycling knowing you’ve extended its useful life and helped reduce its impact on the environment.

Attach your bubble wrap to the inside of an aluminium greenhouse’s frame using greenhouse clips, or for a wooden frame, use drawing pins or a staple gun. Don’t forget to insulate the roof, and make sure to leave the bubble wrap hanging loose across the door so you can get out again! If you have a large greenhouse but you’re only using part of it for overwintering plants, you can section an area off to clad in bubble wrap. Make a screen divide out of bubble wrap or plastic.

A blanket of snow can provide supplementary insulation

Only use insulation if you feel your plants won’t make it through the winter without it because it will reduce light transmission slightly, and light is precious in the darkest depths of winter!

It can be worth insulating the inside of the North side of your greenhouse using a roll of inexpensive thermal insulation foil. This material has bubble plastic sandwiched between two layers of silver foil, and it will reflect both heat and light back into the greenhouse.

Don’t forget the insulating properties of snow. If you experience heavy snowfall, don’t be too quick to dig it all away from your greenhouse (unless it’s in danger of damaging the structure, of course). There’s a good reason it’s often referred to as a ‘blanket’ of snow! You may need to knock it off the sun-facing side of the roof to let more light in.

Bubble wrap can be laid over plants for additional insulation

Insulating Your Greenhouse at Night

Any heat that has built up during the day can be trapped in the greenhouse overnight using a wide range of materials. Purpose-made thermal screens and blinds are expensive, but you can easily make your own night-time insulation.

Double or triple layers of row cover fabric laid directly on top of plants work well. Old blankets and other thick, heavy materials can be suspended on hoops or canes to prevent them from flattening your crops. And thermal insulation foil can be fixed to the inside of the greenhouse roof to help retain heat for longer.

Of course the downside to using materials that aren’t transparent is that you need to remove them promptly to let the light in during the day, but they can be worth it on the coldest nights to give your crops the best chance of survival.

Plastic bottles can be recycled as mini cloches within your greenhouse

Insulating Plants in Your Greenhouse

Cold frames and cloches aren’t just for outdoors – they can also be placed inside the greenhouse to provide an extra layer of protection for your plants.

Alternatively, recycle plastic bottles as mini cloches. Cut them in half and pop each half over individual plants. Any other clear plastic container can be recycled for the same purpose, or use that old faithful, a layer of bubble wrap.

You’ll need to remove cold frames and cloches on mild, sunny days to prevent overheating. Replace them before nightfall to help build up some warmth once again.

Recycle polystyrene boxes to insulate trays of seedlings

Plants in pots are especially vulnerable to having their roots freeze in the cold, and some pots may crack if exposed to very low temperatures. Wrap pots in bubble wrap, or place them in old potting soil sacks and stuff them with scrunched-up newspaper, straw or dry bracken. You can even insulate trays of seedlings in old polystyrene fish boxes, which are often given away free by fishmongers.

Do you have any more tips for ways to keep your greenhouse cozy in winter? If so, we’d love to hear about them – please share them in the comments section below.

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Show Comments


"Fishmongers poly boxes are likely to announce their presence."
Ernest Weston on Friday 3 November 2017
"Fishmongers poly boxes are likely to announce their presence."
Ernest Weston on Friday 3 November 2017
"Quite! They would need a very thorough washing out first. You could always use the polystyrene packaging that comes with electrical goods instead."
Ann Marie Hendry on Friday 3 November 2017
" A good way to insulate also (if you can afford the room they take up) is to fill plastic bottles about 3/4 full of water and place around the walls of the greenhouse. During the day the water heats up from the sun and at night the warm water takes the chill off the air. It is amazing what a difference it makes. "
DeAnna on Tuesday 14 November 2017
"Sigh. Live in an area that has monsoon winds every spring and fall, so can't even HAVE a greenhouse. A few have tried, but they all came down, even the more expensive ones. Our homes have to be built with special roofs here too!"
Grace Towne on Tuesday 14 November 2017
"Great idea DeAnna! People sometimes use barrels of water as heat sinks in greenhouses, but I imagine that lining the walls with water-filled bottles will work even better."
Ann Marie hendry on Tuesday 21 November 2017
"Sorry to hear that the winds are too fierce for greenhouses in your region Grace. Have you considered a plastic-covered polytunnel (hoop house)? They tend to be more robust in strong winds."
Ann Marie hendry on Tuesday 21 November 2017
"Hi Grace, check out walipini greenhouses! They are built in a pit with only the roof protruding, making it much safer in strong winds. I intend building one on our exposed site. Another option is a geodesic greenhouse, as that offers less wind resistance than the traditional structures. "
Vera on Friday 4 May 2018
"where I live I couldn't fill up plastic bottles with water to warm up my greenhouse as the water would freeze up (I live in a cold area in Scotland). The best insulating materiel is bubble wrap or wrap plants with fleece (I use fleece for my tender ferns and jute sacking). Environmental factors determine how to where your greenhouse is situated (usually south facing gets most sunshine and east facing is less sunshine but has the cold wind chill factor)."
sandra Brown on Friday 27 September 2019
"Sandra, in colder areas water-filled bottles are only really effective in spring and summer to help take the edge off the cold - as you say, they'll freeze when temperatures really plummet, and any warmth released by them before than happens is likely to be negligible. "
Ann Marie Hendry on Wednesday 2 October 2019
"Interesting idea, water filled bottles as insulation in wintertime 'al settimo cielo' (in seventh heaven) in Umbria, Italy. do i make a stable outside wall out of them? Can somebody with experience show a foto of the construction?Thanks in advance,cordiali saluti from seventh heaven, Edith"
Edith on Friday 18 October 2019
"A black 55 gallon drum in the GH. soaks the heat up in the day to ade in keeping it cooler and releases the heat back at night"
nigel on Thursday 30 January 2020
"Great idea Nigel, thanks for sharing! "
Ann Marie Hendry on Saturday 1 February 2020
"we tried the black 55 gallon drums 6 of them it didn't work the water froze and damaged some of the drums we live in Alberta , canada , unfortunately we often have long spells of cold "
lone i kabriel on Monday 19 October 2020
"Sorry to hear that Lone. Leaving an 'expansion gap' by not filling the drums to the brim should help avoid problems with splitting when the water freezes and expands, but unfortunately in colder regions it's very hard to keep an unheated greenhouse frost-free, even with insulation and other methods to keep the cold at bay."
Ann Marie Hendry on Tuesday 20 October 2020
"Do 55 gallon drums have enough surface area to absorb/release heat? i wouldn't think so. You would have to find the proper mass/surface area ratio to take advantage of the sun's heat daily cyclic tendencies. "
nick arnold on Saturday 30 January 2021
"I heard an unheated greenhouse can benefit from a compost pile being inside. I am planning on building one this year out of old windows and trying it out. It just might work!"
Michelle on Saturday 24 April 2021
"Compost piles can get pretty hot inside so they are bound to release some of that heat, although I don't find they get very hot in winter. They might do in a greenhouse though, so it's worth a try! Please do let me know how you get on with that."
Ann Marie Hendry on Tuesday 27 April 2021
"Apparently straw bales on the outside of the greenhouse, especially along the north wall can help provide some insulating properties. If used with other measures, such as bubble wrap, reflective foil, heat sink etc. Could help increase the temperature a bit more. I’m planning to build my mini portable greenhouse within my polycarbonate greenhouse to provide an additional layer of insulation and covering crops with frost cloth plus the entire mini GH with a blanket during night when needed. At least that’s the plan!"
Neetu on Monday 25 October 2021
"Great ideas Neetu. Straw bales can be used to make insulating sides for a temporary cold frame with a sheet of glass over the top, so building them up along the outside of a greenhouse sounds like it would help."
Ann Marie Hendry on Wednesday 27 October 2021
"Where can I buy "Purpose-made horticultural bubble wrap has large bubbles and is also UV-stabilized"? I am having trouble finding this except in the UK. Thanks, Tony"
Tony White on Sunday 21 November 2021
"We have a soft sided greenhouse have had it for now 3 seasons live in Utah and it gets rather cold here. lots of snowlots of strongwinds and low freezing temps what we do for the winter is fill the several 5 gallon buckets with rain water from our rain barrels and fill up our Greenhouse with them fill the whole floor up with them and we set the lid on but dont close it tight they dont freeze even though outside it can be 28 deg or lower we have our plants sitting on shelves in there as well as on top of the buckets Everything inside of our greenhouse dont freeze and grows all winter long."
Wandakay on Saturday 22 October 2022
"Sounds like you have a great winter setup working for you Wandakay! Thanks for sharing that."
Ann Marie Hendry on Tuesday 25 October 2022
"Good ideas. Look forward to more! "
Kat on Monday 21 November 2022
"I'm in Texas so don't need extreme cold measures, but I use about 50 1-gallon milk jugs filled with water to line the walls of my hoop house. I place large cardboard pieces between the plastic covering the structure and the water jugs, which insulates them from outdoor cold. If we're having a severe winter storm (in the teens) I'll add reflective space blankets to the roof and sides, which reflects the heat back into the structure. Finally, I use incandescent Christmas lights on the floor and one 250W heating lamp placed centrally that is triggered by a thermostat if the inside temp gets to 38 degrees (not very often). Overall, the hoop house is usually about 10-15 degrees warmer than the outside temperature using these methods."
Constance on Wednesday 1 February 2023
"Great tips Constance, thanks for sharing! "
Ann Marie Hendry on Thursday 2 February 2023
"If you have chickens, bringing some at night in to a cage under the bench can help."
Wayne on Wednesday 22 February 2023
"Great suggestion Wayne. Cosy chickens = cosy greenhouse!"
Ann Marie Hendry on Friday 24 February 2023

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