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Unheated greenhouse – does it really make a difference?

polycarbonate greenhouse

I was going to give you a very quick update on the garden today as things do seem to be coming along nicely but in looking at the photos to post it struck me that there is maybe a topic I could talk about that might be of help to some gardeners who are thinking about greenhouses. Namely does it make a difference. It’s something I wondered about when I was looking to buy our greenhouse as I couldn’t afford any of the top of or near top of the range models and I had no way of heating or controlling temperatures in there so I did wonder if an unheated greenhouse would make any difference. Well in short, the answer is yes actually it does and I’ll explain why.

My greenhouse is a lower end poly carbonate model, this means that instead of glass panels it has thin, clear, plastic panels on the sides and corrugated plastic panels on the roof. The first obvious benefit of this is that plastic is less prone to damage than glass and secondly should you need to replace it it’s also cheaper. If you’ve read the posts about storms in our neck of the woods and how it rips the roof panels out of the greenhouse then you know that cheap is a good thing.

I’ve never owned a glass greenhouse so I can’t compare poly carbonate to glass for you, I can only talk on my own experience and that is that when it’s cold, the greenhouse is cold. It’s unheated and as much as we did our best when we put it together there are a few small gaps in the construction that let the cold in. However in saying that if there is a little bit of sun, the greenhouse really does hold onto that heat, there is a marked difference in temperature outside and inside with even just a little bit of sun.


It was actually when I was planting my peas last weekend that I realised the difference this year and decided that it might be a topic worth talking about on the blog. The first photo here is some peas that I planted directly into the pots outside. They are beginning to show and as I write this blog they are all above ground, for this time of year that’s pretty much on que as expected. However when I show you the next picture which is the peas which were sown at the same time but in the greenhouse, you can really see the difference.

Like I said these ones were planted on the same day but obviously have come on so much more than the ones sown directly into soil outside.

And it’s not just peas, I see this with everything. I regularly plant courgettes in the greenhouse and when the threat of frost is past I then put them outside. A colleague this week commented on the size of my courgettes, apparently compared to her outdoor ones, mine are monsters. I’ve always done this so I don’t have any outdoor photos to show you to compare but here are my courgettes as of 28th April.


There is one smaller plant as you can see, this was a bit of a late one to take off from seed but I’ve kept it as I thought it’d be an interesting comparison this year.

So there you go. Unheated, poly carbonate greenhouse, it really does make a big difference.

Oh and one more thing, it’s great for over wintering plants that don’t like frost and snow, we just move them into the greenhouse before the bad weather starts to protect them.

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