How to clean a greenhouse – an expert guide to banishing green algae, dirt and grime

If you're lucky enough to own one, it's important to take the time to learn how to clean a greenhouse – because, while it might not be one of the most glamourous of winter gardening ideas, it's one of those essential jobs that will see you in good stead for the growing season ahead.

One of the top things you need to know before buying a greenhouse is this: the most important thing you can do to keep yours in order – more so than any of the DIY greenhouse ideas you've been ogling – is give it a thorough deep-clean once a year.

With that in mind, then, it's time to learn how to clean a greenhouse so it looks its very best (and makes you the envy of all your neighbours, too).

How to clean a greenhouse

Now, in an ideal world, the best time to clean a greenhouse is always when it suits your plants. If you use yours to grow your own fruit and vegetables, for example, winter is a great time to give it the once over as your crops should be finished.

If your greenhouse is a one-stop destination for raising seedlings, you'll want to clean in between crops (autumn or spring). And, if you use your greenhouse for overwintering purposes, it's best to wait until it's warm enough for your plants to survive outdoors before you get to work (again, autumn is ideal).

Still, if you've followed Monty Don's greenhouse advice to the letter and avoided heating yours this winter, you're in luck: a sunny windowsill or sheltered spot with a little added fleece protection should be more than enough to keep your plant babies thriving while you get down and dirty.

What you will need

Before you start learning how to clean a greenhouse, it's important to gather together all of the tools and products you will need to get yours looking beautiful.

With that in mind, then...

• A garden brush like this wooden brush from Amazon
• A vacuum cleaner (check out our pick of the best cordless vacuum cleaners if you need help choosing one for your needs)
• White vinegar, like Miniml White Vinegar from Ocado
• A soft sponge or cleaning cloth
• A pair of rubber gloves, like the Marigold Outdoor Tough Gloves from Ocado
• A bucket of warm water

Step-by-step

Now that you have all the tools you need at hand, it's time to get to work – just be sure to remove any plants from your greenhouse before you get started, and pop them in a sheltered spot to keep them safe while you're hard at work.

'Before you get stuck in, remove all plants, pots and tools from inside to give you clear access to the structure, as well as to protect them from water damage. Once it is empty, it’s time to get cleaning!' says Nelly Hall, brand director at premium bespoke glasshouses manufacturer Alitex.

Let's get this show on the road...

1. Brush or vacuum the area

It's important to brush or vacuum the floors and hard surfaces of your greenhouse's interior, to ensure that all excess soil and debris is out of the way.

'Sweep the base and clear away any debris, such as compost, leaves or organic matter, from shelving, and pop it in the compost bin,' says Nelly.

'Get all the dust out of there, and especially focus your attention on removing any dead matter, too, as it can rot and spread diseases around your plants,' agrees Christopher O'Donoghue of Gardens Revived.

Christopher O'Donoghue

A gardener with over a decade of experience under his belt, Christopher set up Gardens Revived with his brother, Andrew, in 2018  to create a thriving family business. Together, they have worked on residential gardens, listed buildings and gardens, flower shows and large estates with some exceeding 70 acres – many with historical significance.

Don't neglect the corners and frame edges, as this is where cobwebs and debris tend to collect. And Christopher says he also uses a 'plastic plant label' to ease out any dirt trapped between panes, too.

2. Remove weeds

You don't need to learn how to kill weeds like a pro, but Christopher says you will want to 'pull out any weeds or unwanted plants growing in the greenhouse' during the cleaning phase, too.

3. Wash surfaces

Next on the agenda, of course, is washing your greenhouse down – inside and out.

'To wash your greenhouse, use warm, soapy water to remove any dirt and grime that has built up over time,' advises Lucy Rhead, gardening enthusiast and Marketing Manager at Gtech. 

Lucy Rhead

Lucy has worked at Gtech for more than five years during which time she’s developed a passion for cleaning and gardening. Lucy loves learning about new product innovations, and how they can help make everyone’s lives a bit easier.

'Make sure to use a plant-friendly soap for this to ensure that high levels of salt and chemicals do not build up in the soil around your greenhouse, as this could damage any plants nearby and impact their growth,' Lucy continues.

This caveat in place, she goes on to share her top cleaning tips and tricks, noting that that you should 'use a soft sponge or cloth with the cleaning solution to wipe down the glass panes' – and pay especial attention to any green algae (more on that later).

Nelly adds that it's best to tackle this job on a sunny day, as it will help everything to dry that much quicker, and that 'an extendable handle or garden ladder may be useful to help you reach the upper panes and roof safely.'

4. Disinfect

If you're learning how to clean a greenhouse, you'd be well advised to take your lead from the Royal Horticultural Society (RHS) and use a hydrogen peroxide based product to disinfect the area.

'Garden disinfectants, such as Jeyes fluid outdoor cleaner from Amazon, are satisfactory,' they say.

It's also a good idea, Christopher says, to 'wash and sterilise pots, trays, and tools used in the greenhouse'.

7. Don't forget the guttering

When sussing out how to clean a greenhouse, Nelly reminds us that it's important not to 'forget to give the guttering and water butt a clean too'.'

'Fallen debris such as leaves can easily cause blockages and prevent water from flowing freely,' she says.

'Simply scoop out any matter clogging up the gutter and rinse it through with clean water.'

6. Inspect for damage

Finally, check over your greenhouse for any damaged or broken parts, and replace and repair as needed. 

'You should also check and clean the ventilation systems and fans in your greenhouse,' says Christopher.

Then, all that's left to do is return your plants, arranging them neatly and strategically for optimal growth. 'Use this as an opportunity to get organised ahead of the growing season,' says Nelly. 

'Check over your tools, give pots and seed trays a wash, and take stock of any leftover seeds. This will leave you in good stead to get planning what you’d like to go this year.'

FAQs

Why is it important to clean a greenhouse?

'Giving your greenhouse a deep clean once a year is really important – not only will it make your time spent tending to plants more enjoyable, but it will also help maintain a healthy growing environment and reduce the risk of pests and diseases,' says Nelly.

A clean greenhouse will also 'let more light in,' notes Christopher, 'which is essential for growing healthy plants.'

How do you get rid of green algae in a greenhouse?

'If you have green algae forming in your greenhouse, it can be scrubbed off with either warm, soapy water or a diluted vinegar solution,' says Lucy. 

'Simply use whichever solution you have available and a bristle brush to remove it. To prevent the build-up of green algae going forward, try to improve ventilation, reduce humidity and ensure that there is enough space between your plants.'

Lucy goes on to stress that 'regular cleaning of your greenhouse will also help to prevent any algae build-up in the future'.

Can you use vinegar to clean a greenhouse?

'Vinegar is a great natural alternative to harsher cleaning products and can be used as a disinfectant to help prevent pests and the spread of plant diseases in your greenhouse,' says Lucy. 

'Simply mix one part white vinegar with one part water to form a solution.'

She adds that, 'while vinegar is less harsh than many store bought cleaners, it’s important to still be careful where using the solution in your greenhouse'. 

'Make sure it does not come into any direct contact with your plants, as the acidity of the vinegar could harm them.'

Can I use bleach to clean my greenhouse?

Bleach can be used to clean your greenhouse effectively, but it must be used with care. 

'It should always be diluted significantly, using one part bleach to nine parts water,' says Lucy. 

'The solution can then be used to disinfect plant pots, trays, tools and any surfaces in your greenhouse that have come into contact with plant pathogens.'

If using bleach, Lucy says it's important to 'make sure your greenhouse is well-ventilated and that you are never mixing it with any other chemicals or cleaning products'. 

'After cleaning, rinse any surfaces to ensure that there is no bleach residue left behind as it could harm your plants if they come into contact with it,' she finishes.

Now that you know how to clean a greenhouse, you can set to work making yours the sparkling bauble that adorns your garden.

Just be sure to save any old plant debris for your compost heap; it is, after all, called 'brown gold' by gardeners for a reason!