So how hot does my greenhouse get?

I’m starting to get organised for the colder months coming and I’m spending a bit of time taking stock of the garden, of what’s hardy and can stay outside and what will need a wee bit of love and support once the weather turns. I’ve started planning what I can grow and where and even a bit of an experiment. It’s been relatively comfortable in the greenhouse most days so I thought I’d take advantage and sow some carrots in the root trainers in the hope that I can get them growing and plant them out before the frosts hit. The plan being that I should then have some carrots early on in spring. So I’ll be getting those sorted this week.

So the temperatures are changing, we’re getting into Autumn and I’m very aware of that. Instinctively a lot of us greenhouse growers are starting to wonder what we can do over the cold months and if our greenhouses can help. And… folk who maybe are thinking of greenhouses are wondering what kind of a difference they really make. Thinking about that though, I bet there are quite a few of you out there, who like me, haven’t really considered how we know what temperature our greenhouse sits at in specific periods of the year. And being me, I had to go do some research, cause I don’t like not knowing stuff.

Now here’s the funny thing, normally our blogs and videos are about sharing our experiences when we’ve got to the end of something and discovered something a new interesting thing we want you guys to know. Today we’re turning that on its head and we are all starting at the same point. So today is about the journey of learning about your greenhouse temperatures and how to measure it properly. Cause I bet a whole bunch of you (me included) were getting this wrong.

So firstly then, let me bust a wee myth. This is something that appears in the comment section of our videos often and I think is probably, more generally, a misunderstanding out there – at least amongst folk who haven’t yet bought a greenhouse or polytunnel. The purpose of a greenhouse or polytunnel isn’t to raise the temperature of the growing area, although yes, in the hot months when the sun is out it does do that but…..in the colder months, unless you have a heating system, the greenhouse is pretty much the same temperature as outside Most of the time. If it’s sunny, maybe a little bit warmer. You can’t expect to carry on growing as normal just because you have a greenhouse. So what is the point of a greenhouse? Well, it’s actually about being able to control your environment. So about being able to say ok these particular plants will be happy in this type of environment and I can create that here And I can create it reliably.

So that’s why would we be interested in monitoring the temperature?

If we can monitor the temperature in the greenhouse, we can get to know the environment so that we can make decisions about what we grow and when. It takes some of the grow and hope element away. And also if we can keep an eye on the temperature we know when any fluctuations happen or when the big changes occur each year so we can take action.

And how do we measure temperature?

So here’s the thing – and I am not asking anyone to name themselves and own up to this here. It’s our little secret but… it is super common for us to buy a thermometer for keeping an eye on the temperature in the greenhouse and we stick it up on the wall or on a shelf and look at it every so often on a hot day for that little buzz of seeing how hot it is. Loads of us have done this. But here is the thing, as much as that’s a bit of fun, it’s not actually a very good way of telling the temperature in the greenhouse. And here’s why.

So different areas of your greenhouse will actually be different temperatures. Imagine say, you have a thermometer hanging on the wall (frame). It may actually get hit with a sunbeam at some point throughout the day and that will make the temper reading on it shoot up.

In contrast, you might have one on a low shelf, in shade, so as you can imagine that might then show a cooler temperature. So which of these are right?

But you also might want to think about why you are taking the temperature. For instance, in spring, if you are sowing seeds. The big thing you need to think about is when the soil if the correct temperature to encourage those little seeds to germinate. How do you know that just by measuring the ambient temperature around the greenhouse? In those instances, you may prefer to measure the soil temperature.

We can go even further, right now, in September, I am very aware that the temperatures, generally, are dropping. However, I need the greenhouse to hold a nice 20 – 25C in order for my tomatoes to ripen. So I want to measure the temperature around the level of the greenhouse where my tomatoes are, not low down or under a shelf and not the soil temperature.

Does it make sense now?

Now the last thing I am going to mention is monitoring verses taking temperature and this is something I’ve never done before, to be honest cause it was too much hassle. But monitoring my greenhouse over a period of time will help me get to know the environment and what I can do with it, or even if I decide to make changes. Monitoring is not impossible with traditional thermometers, it just means taking a note of the temperature at various points of the day and recording them. Over a period of time you will start to build a bank of data which you can use to look for patterns. However, I am lazy! So instead I’m using a digital thermometer that sends the info to me so that it is stored and recorded on my phone and displays this in graphs. All the hard work is done for me and it’s actually really interesting.

OK scrap that, it’s addictive. I can’t help myself from checking it multiple times a day. But it is a bit of fun as well.

So I have now found out that at the moment, when it rains, the temperature in my greenhouse drops a lot, but when the sun is out, it also rises quite a bit. Overnight at the moment it is dropping to 8C. That’s a nice safe temperature, but I will be able to monitor this for winter and be ready with the fleeces when it threatens to be get properly cold.

This is going to be a really interesting journey to learn about my greenhouse and the growing I can do and I hope it might inspire you guys to join me in the fun.