How to Protect Pelargoniums (Geraniums) Over Winter – Our Complete Guide to Overwintering

Pelargoniums might fill our greenhouses and gardens with colour throughout the summer, but there is one thing they really don't like — frost!

Over the years we've learnt a few lessons (some of them the hard way!) about getting our Pelargonium collection safely through the British winter, so in this guide we're sharing some of the things we do here at Growing Crazy to protect our plants when the temperatures start to tumble.

Please note: this guide contains some affiliate links. We only recommend products that we use, have used or genuinely think may be useful, but we may receive a small commission if you make a purchase through one of these links.

How cold is too cold for Pelargoniums?

Pelargoniums are not frost hardy, so the most important thing is to keep them frost free throughout the winter.

Where possible, we aim to keep our growing spaces at around 5°C or above. Your plants don't need tropical temperatures — in fact, keeping them too warm can encourage soft growth during the darker winter months — but they do need protection when temperatures head towards freezing.

A cool, bright and frost-free greenhouse is ideal.

And don't forget that keeping Pelargoniums alive through winter isn't just about temperature. During the colder months they need much less water, good air movement and plenty of light. Cold, wet plants can quickly develop problems with rotting, so we tend to keep ours considerably drier during winter.

We've learnt this one the hard way!

The photograph below shows one of my favourite plants, Pelargonium ardens, after a heater failure.

It quite literally froze solid in its pot.

Unfortunately, it didn't recover and we lost the plant completely. :-(

That experience made us rethink how we protected the collection. Rather than relying on a heater alone, we now try to have several layers of protection — and, importantly, ways of knowing if something has gone wrong.

After all, a greenhouse heater is fantastic... right up until the night it decides not to work!

Horticultural Fleece — simple but incredibly useful

One of the simplest things we use during particularly cold weather is horticultural fleece.

We already insulate some of our growing spaces with greenhouse bubble insulation, but fleece gives us another layer of protection directly around the plants.

By laying fleece over the plants, you create a slightly more protected microclimate underneath and help retain some of the warmth around them.

On particularly cold nights we put the fleece over the plants before the temperature really starts to fall, ideally towards the end of the afternoon while there is still some warmth around to trap underneath it.

And we know it works!

When we had the heater failure that caused temperatures inside one of our greenhouses to fall to around -4°C, we lost a number of plants. However, many of those underneath fleece survived.

We are convinced we would have lost considerably more without it.

Sadly, my P. ardens wasn't underneath the fleece that night!

After that experience, you could probably say we became slightly enthusiastic about fleece...

We use a horticultural fleece similar to the type available here on Amazon: Horticultural Fleece.

Heating your greenhouse

If you're overwintering Pelargoniums in a greenhouse, some form of heating may be necessary depending on where you live and the type of greenhouse you have.

You don't necessarily need to make the greenhouse warm. Our priority is simply to provide enough heat to prevent temperatures falling to damaging levels.

The size and construction of your greenhouse will make a big difference to the amount of heating required, so make sure any heater you choose is suitable for the space.

Electric greenhouse heaters

In our smaller propagation greenhouse we use an electric fan heater with a built-in thermostat.

We've used an Elite Hotbox fan heater, which has the added advantage of circulating the air while heating the greenhouse.

Air movement is useful in winter because stagnant, damp conditions can encourage fungal problems — and we can also use the fan without heat during warmer weather to improve air circulation.

If you're using an electric heater without its own thermostat, an additional digital temperature controller can be useful.

Rather than having the heater running unnecessarily, a thermostat allows it to operate when temperatures fall to the level you've set — potentially helping with energy consumption as well as protecting your plants.

Heating larger growing spaces

For some of our larger growing areas we've also used propane greenhouse heaters.

We use Shilton greenhouse heaters, which have built-in thermostatic control.

Whatever heating system you choose, the important things are that it is suitable for the size of your growing space, installed and operated safely, and reliable enough for the conditions you expect during winter.

And that brings us to something we now consider just as important as the heater itself...

Keep an eye on the temperature!

A good maximum/minimum thermometer is one of the most useful bits of kit you can have in a greenhouse.

It doesn't need to be complicated or expensive. Being able to see how low the temperature dropped overnight gives you a much better idea of what is actually happening inside your greenhouse.

You might be surprised!

   

For years we used standard greenhouse thermometers, and we still do, but after experiencing some particularly cold winters we wanted something that could actually warn us when there was a problem.

That's when we started using Wi-Fi temperature monitoring.

Our winter game changer — temperature alerts!

We installed a Govee Wi-Fi Thermometer in our growing space and it has genuinely become one of our most useful bits of winter kit.

It connects to an app on my phone, which means I can check the greenhouse temperature without having to head outside in the middle of a freezing night.

Even more importantly, we can set a low-temperature alert.

If the temperature falls below the level we've set, my phone lets me know and we can investigate before the plants are damaged.

And it has already saved us!

On one particularly cold night, the gas supplying a heater ran out earlier than expected. The temperature started to fall and the alert came through on my phone.

We were able to get down to the greenhouse, sort out the problem and get the temperature back under control before it dropped below freezing.

Without that alert, we probably wouldn't have known anything was wrong until the following morning.

After the experience of losing plants when a heater failed, having that extra warning gives us a little more peace of mind.

What if your greenhouse doesn't have Wi-Fi?

This was exactly the problem we had!

We didn't have an internet connection in the greenhouse, so we used an old 4G Wi-Fi router with a pay-as-you-go SIM to create a connection.

Something similar to this D-Link 4G Router can do the job.

Depending on your setup and how far the greenhouse is from your house, a Wi-Fi extender or other solution may also work.

The important thing is that if you're relying on a smart thermometer for alerts, make sure the connection itself is reliable.

Don't forget about watering

It is very easy to concentrate on keeping Pelargoniums warm during winter and forget that overwatering can be just as troublesome as the cold.

As temperatures and light levels fall, the plants use considerably less water.

We allow our plants to dry between waterings and keep them much drier through the coldest part of winter.

The combination we really want to avoid is:

Cold + wet + poor air movement.

That's when rotting and fungal problems can quickly take hold.

Remove dead or yellowing leaves regularly, keep the growing area clean and give the plants as much light and ventilation as conditions allow.

Our winter Pelargonium checklist

When really cold weather is on its way, these are the main things we're thinking about:

• Keep plants frost free — ideally around 5°C or above.
• Watch the forecast, particularly overnight temperatures.
• Use fleece as an additional layer of protection during very cold spells.
• Monitor greenhouse temperatures with a maximum/minimum thermometer.
• Consider remote temperature alerts so you know if something goes wrong.
• Check heaters and fuel supplies before a particularly cold night.
• Reduce watering as growth slows.
• Maintain air movement and ventilation whenever conditions allow.
• Remove dead leaves and flowers to keep plants clean.
• And if you have a particularly treasured Pelargonium, take a few cuttings as insurance!

We have hundreds of different Pelargoniums to get through the winter here at Growing Crazy, so we're always looking at ways of improving how we protect them.

We've also learnt that you shouldn't rely on just one thing.

Heating is important, but combining it with insulation, fleece, temperature monitoring and good winter growing practices gives your plants a much better chance of making it safely through to spring.

Then, as the days get longer and temperatures start to rise, you can gradually increase watering and get them growing strongly again ready for another summer of fantastic flowers!

When can Pelargoniums go back outside?

Don't be in too much of a hurry to put your Pelargoniums back outside in spring.

Wait until the risk of frost has passed in your area. Traditionally gardeners often waited until around the end of May, but your local weather forecast is much more useful than working to a fixed date.

Hopefully some of the things we've learnt protecting our own collection will help you keep your Pelargoniums happy and healthy this winter too.

Happy growing! 🌿