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Get your greenhouse sparkling clean and ready for another season of growing. Includes information on greenhouse pests and pathogens, eco-friendly cleaners, and getting rid of algae and moss. Includes a video at the end.
For us veggie gardeners, a bright and dry day in late winter is the best time to give the greenhouse a deep clean. In winter you won’t have as much pressure with other gardening tasks, there are likely to be few plants in the greenhouse, and a clean greenhouse can really get you excited about spring sowing. But other than a burst of enthusiasm, why bother cleaning the greenhouse at all?
Over the gardening year, moss, algae, lichens, dirt, and pests can colonize your greenhouse inside and out. Sometimes it’s noticeable, and sometimes it’s subtler. It’s best to clean either way since growth left after the winter can explode into life once warmer days arrive. This slimy takeover can cause a few issues for you.
Moss and algae create issues in the greenhouse
The big two, moss and algae, reduce the amount of light coming through the glass. Though neither directly harms plants, they do compete for nutrients and can attract fungus gnats.
If algae begin growing in compost then it can quickly colonize the surface, turning it green. This can reduce the amount of air getting into the compost and slow root growth. Fungus gnats eat the algae and in turn can transmit pathogens to your plants through their mouths.
Reducing pests and disease
Greenhouses are semi-closed, sheltered environments that make it easier for plants to grow. They also provide the perfect habitat for plant fungus and pathogens to take up residence. The University of Vermont compiled a guide on greenhouse pathogens, what to look for, and how to avoid them in the greenhouse. Control of all of them include sterilizing equipment and tools, removing affected plant material, and growing in a clean and sanitary greenhouse.
- Powdery mildew, often seen as a powdery white residue on plants’ leaves. It’s a fungus that lurks in affected plant material, live and dead, and comes in on the air.
- Botrytis, a fungal growth that kills leaves and can leave them covered with a type of brown to grey ‘mold’. Again, it likes warm and humid conditions, and attacks damaged and young plants causing them to die off. Botrytis is the cause of ‘damping off’
- Rusts, which look like rusty speckles on leaves. Severe attacks can stunt growth and kill plants.
Slugs, snails, and insects
Aside from the fungus gnat issue attracted by algae, and plant pathogens that lurk in plant material and grime, there are also our more familiar foes slugs and snails. You think you don’t have a problem with them in your greenhouse until you remove everything from it and do a deep clean. Just this week I found quite a few slugs and their eggs while cleaning my own greenhouse.
Other pests that can be cleared by a deep clean include red spider mites, white fly, aphids, caterpillars, and mealybugs. This is because many of them overwinter as eggs. You can clear them out by washing the entire greenhouse, changing compost, and spraying down pots and trays.
Cleaning the greenhouse gives it a fresh new start to the gardening year with a lot less threat to our plants. If you’re battling with another type of pest in your greenhouse, the University of Kentucky has a list of types common in the USA and how to deal with them.
How to Deep Clean the Greenhouse
Deep cleaning the greenhouse begins with removing everything, or the majority, of what’s inside. Then it’s a matter of cleaning it from top to bottom. Remove as much dry material as possible before introducing wet. The same goes for the outside – clean top to bottom with the aim of clearing anything that’s obscuring the glass or working its way into the wooden or metal frame. After this it’s a matter of cleansing and that can be done in a manner of ways. The end result should be a sparkly clean greenhouse that your new spring plants will thrive in.
Check-list for cleaning the inside of the greenhouse
These are the steps that I use to clean my greenhouse. I’ve used them on both my current glass greenhouse and the plastic poly-carbonate greenhouse I’ve had for the past few years.
- Remove all plants, pots, and everything else from the greenhouse. Use this time to look under all of them for overwintering slugs, eggs, insects, and to clean everything thoroughly.
- Sweep the greenhouse from the top to the bottom. If you’ve had disease in your greenhouse the year before, dispose of plant material in the bin, not the compost pile.
- Pre-scrub all surfaces of larger pieces of algae, moss, and other growth. Sweep again if necessary to remove all of this material.
- Fill a bucket with warm soapy water, I use ordinary Ecover washing up liquid, and scrub all surfaces beginning with the top of the greenhouse and working down. Use an old toothbrush for smaller nooks and crannies and a scrub brush for everything else.
- Scrub off any old shade paint
- Rinse well with clean water.
- Scrub and rinse the floor and then allow everything to dry.
- After it’s dry, you can use a homemade vinegar spray to further disinfect and to give glass a sparkle.
Using Algon to stop algae growth
This year I’ve also applied non-toxic Algon to both the inside and outside of my greenhouse glass. It’s safe around pets and wildlife and won’t hurt aquatic life either. Best of all, it can help stop regrowth of algae for months to come. One word of caution though – it’s not recommended for application to metal. As you’ll see in my greenhouse cleaning video (at the end of this piece) I wiped all the metal parts down with a damp rag afterward.
Removing algae from between panes of greenhouse glass
One conundrum that I faced with my most recent greenhouse clean is getting rid of the algae growing in between the glass panes. In my traditional glass greenhouse, the glass panes overlap one another and the area between was pretty much solid green.
If you have a week to deep clean the greenhouse, you could potentially remove all the panes and clean them individually. My time is limited so I used the next best option – a plastic plant label. You just wiggle it in between and push the algae out. It works a treat. A blast of water from the hose pushes the rest of it out.
Check-list for cleaning the outside of the greenhouse
Cleaning the greenhouse’s exterior also includes cleaning the drains and the water butts. Both of these areas are places algae will live and using saved water can reintroduce algae to the inside of your greenhouse.
- Sweep all leaves, moss, and debris from the greenhouse roof, gutters, sides and the surrounding area.
- Scrape off as much moss and thicker material from the glass as possible. You’ll need a long-handled brush, scraper, and/or ladder.
- Scrub the top of the greenhouse with soapy water then work downwards and scrub the gutters out.
- Scrub the sides of the greenhouse and make use of that toothbrush if need be
- Rinse it all off and let dry
- Bail the water out of the water butts and give them a good wash too. If you have a downspout connecting the gutters to the water butts it would be a good idea to clean them out too. A rag wrapped around a broom handle does the work well enough.
I also sprayed the outside of my greenhouse with Algon this year. The glass needs to be completely dry and there should be no forecast of rain.
Deep Cleaning the Greenhouse with eco-friendly products
I’m adverse to using products that are anti-bacterial or that are made from ingredients that will harm plant and animal life. A simple liquid soap, especially an eco-friendly choice like Ecover, or a similar brand, is just as effective.
Anti-bacterial soap is a bad idea for home use. Why? Because it kills 99.9% of bacteria. The remaining 0.01% will be resistant and breed and can create super bugs. Ordinary soap washes microbes away without supercharging their evolutionary arms race.
Conventional greenhouse cleaners
There are four types of cleaners that have been used for years to clean greenhouses. They’re mainly employed to kill bacteria and microbes but a good wash with soapy water can be just effective. Unless you’re battling with a tough disease, fungus, or mold infestation in your greenhouse, I’d avoid using these as part of the general greenhouse clean. It may be wise to consider their use for tools, work benches, and propagation areas though.
- Bleach. Although there isn’t evidence of it directly affecting the environment, its manufacture is not eco-friendly. It also stinks and can stain your clothes.
- Alcohol (70% Isopropyl), a solvent that can cause irritation through skin contact or inhalation. Use it for sanitizing tools, but it’s probably overkill to use it throughout the greenhouse.
- Hydrogen dioxide, aka Hydrogen peroxide. This substance is in quite a few branded greenhouse and garden tool products and is useful in disinfecting wounds. Again, consider using it for tools but it is probably unnecessary for overall greenhouse cleaning.
- Quaternary ammonium chloride salt. You’ll find this compound in a few branded garden cleaners but it’s really not a great idea to use it. QACs are persistent in the environment and can affect aquatic life. They also persist on cleaned surfaces and waste water, both of which can cause skin irritation
Ah, steam cleaning. Some folks talk about their steam cleaners as if they were a member of the family. I’ve yet to convert to the steam cleaning revolution but if you have, use that thing in the greenhouse too. Just make sure to give it a good dry scrub and remove all the larger bits of debris before you begin.
There’s no more satisfying activity than using a pressure washer to clean the patio. I’ve been known to pressure wash for hours without showing any sign of fatigue – the adrenaline of seeing the original colour of the paving stones just keeps me going. Yeah, weirdo alert.
I personally would not use a pressure washer on my greenhouse. There are many that do but the chance of glass breaking is just too great in my opinion. If you use a pressure washer on your greenhouse let us know in a comment below, along with any tips.
If you found this piece useful and are looking for even more ways to tidy the garden have a read of How to use the Marie Kondo Method in the Garden.