I’ll be honest: for the first two years I owned my greenhouse, I never cleaned it. Not once. The glass went grimy, algae crept across the staging, and I couldn’t figure out why my seedlings kept damping off and my tomatoes looked so miserable. Then one February weekend I finally gave the whole thing a proper scrub — and the difference that spring was embarrassing. Seedlings I’d assumed were just “difficult” suddenly thrived. If you take one thing from this guide, let it be this: learning how to clean a greenhouse properly is the highest-return job in the gardening year.
How to Clean a Greenhouse: Table of Contents
Why Cleaning Your Greenhouse Matters So Much
A dirty greenhouse isn’t just unsightly — it actively works against your plants. The biggest issue is light. A film of algae, dust, and grime on the glass can block a shocking amount of sunlight — some estimates say up to 30–40% in winter, exactly when your plants need every photon they can get. Weak light means leggy seedlings, slow growth, and poor fruiting.
Then there’s disease. Greenhouses are warm, humid boxes — paradise for fungal spores, bacteria, and overwintering pests. Old plant debris, dirty pots, and algae-covered staging harbour all of them. Many cases of damping off, grey mould, and pest explosions trace back to a greenhouse that hasn’t been cleaned in years. A thorough annual clean breaks those pest and disease cycles before the growing season starts.
Finally, there’s simple practicality. Cleaning forces you to inspect everything: cracked panes, perished seals, blocked gutters, wobbly staging. Catching those in February beats discovering them in a May storm.
When to Clean Your Greenhouse: Timing It Right
The classic advice — and I agree with it — is to clean twice a year. The main deep clean happens in late winter or early spring (February to March), after the worst of the cold but before you start sowing and potting in earnest. Everything is empty or nearly empty, the days are getting longer, and you’re setting up a pristine environment for the season ahead.
The second clean comes in autumn (September to October), after summer crops finish. This one’s about removing spent plants, clearing algae that’s built up over summer, and checking the structure before winter. Since you’re reading this in autumn, you’re right on time for that second clean — it’s the perfect weekend job before the weather turns.
Pick an overcast, mild day if you can. Bright sun dries cleaning solution too fast (leaving streaks) and makes the glass uncomfortably hot to work on. Avoid frosty days too — cold water on cold glass risks cracking panes, and you don’t want disinfectant freezing before it works.
What You’ll Need Before You Start
You don’t need specialist equipment. Here’s my kit, gathered over the years:
- A bucket, warm water, and washing-up liquid (mild detergent)
- A soft sponge or cloth, plus a long-handled soft brush or mop for the roof
- A squeegee for streak-free glass
- A stiff broom and dustpan
- A garden hose with a spray nozzle
- Disinfectant: horticultural disinfectant (like Jeyes Fluid, used at the proper dilution) or a mild bleach solution
- Rubber gloves
- A step ladder (stable, on level ground)
- Bin bags for debris
What to avoid: pressure washers on glass (they crack panes and blast out glazing clips), abrasive scourers on polycarbonate (they scratch it permanently), and harsh solvents. Warm soapy water does 90% of the job.
Step 1: Clear Everything Out
Start by emptying the greenhouse as completely as you can. Move overwintering plants outside for the day if the weather’s mild, or cluster them in a sheltered corner covered with fleece. Remove heaters (switch off electrics first), thermometers, trays, and anything portable.
Now be ruthless with debris. Pull out every dead plant, fallen leaf, old grow bag, and scrap of twine. Sweep up all the loose material from the floor and staging. This matters more than it looks — organic debris inactivates disinfectants later, and pests overwinter in exactly this kind of clutter. Bag it all and bin it (don’t compost diseased material).
Step 2: Clean the Glass From the Inside
With the greenhouse empty, wash the glazing from the inside first. Use warm water with a few drops of washing-up liquid and a soft sponge, working top to bottom so dirty water runs down over uncleaned areas. For the roof, a soft brush or mop on a long handle saves your shoulders.
Pay special attention to the glazing bars and overlaps where algae and moss collect — a soft brush gets into those crevices. Rinse with clean water from the hose. If you want a streak-free finish, follow with a squeegee while the glass is still wet.
For polycarbonate panels, the same soapy-water approach works — just never use abrasive pads or solvent-based cleaners, which cloud the surface permanently. If you have particularly stubborn algae, a second pass with the disinfectant solution (Step 5) handles it.
Step 3: Scrub Frames, Staging and Surfaces
Now tackle the structure itself: aluminium or wooden frames, staging slats, shelves, and sills. Warm soapy water and a sponge or brush do the job. Wooden staging deserves extra attention — scrub between the slats where algae and old compost lodge, and check for rot while you’re at it. A soft brush is ideal for textured surfaces.
This is also when I oil or treat any wooden staging if it needs it (let it dry fully first), and tighten any loose screws or bolts on metal staging. You’re already up close — it takes seconds.
Step 4: Clean the Floor Thoroughly
The floor is the dirtiest part of most greenhouses and the biggest reservoir of pathogens, so don’t skimp here. Sweep thoroughly first, getting right into the corners and under the staging. Then hose or mop the whole floor with warm soapy water.
For soil or gravel floors, rake off the top layer of debris and consider replacing the top few centimetres of gravel every few years — it harbours more than you’d think. For concrete or slab floors, a stiff broom and soapy water, followed by the disinfectant rinse in Step 5, leaves them properly clean.
Step 5: Disinfect Everything
Cleaning removes dirt; disinfecting kills what’s left. Once all surfaces are clean and while they’re still damp, apply your disinfectant. I use a horticultural disinfectant diluted exactly as the label says — “more is better” is not true here; too strong damages plants and irritates your lungs. A diluted bleach solution also works, but rinse thoroughly afterwards.
Spray or wipe it over glazing bars, staging, sills, door handles, and the floor. Don’t forget the propagator, seed trays, and pots you’re putting back — wash them in disinfectant too, since dirty pots are a classic source of damping off in seedlings. My guide on preventing damping off in greenhouse seedlings explains exactly how dirty equipment spreads the problem.
Ventilate well while the disinfectant works, wear your gloves, and keep it away from any plants still inside. Let everything dry naturally before bringing plants and equipment back in.
Step 6: Clean the Outside — Glass, Gutters and Frame
Now step outside. Wash the exterior glazing the same way — warm soapy water, soft sponge or mop, squeegee for the finish. You’ll be amazed how much brighter the interior feels after this.
Clear the gutters of leaves, moss, and sludge — blocked gutters overflow down the walls and create exactly the damp conditions that breed algae and rot. Check downpipes run clear. While you’re up the ladder, inspect the roof: slipped panes, cracked glass, perished glazing clips, damaged seals. Replace or repair now, before winter winds find the weak spots.
Give the door a once-over too — clean the runners or hinges, check it closes properly, and make sure vents open and close freely. An automatic vent opener that’s seized shut is useless.
Step 7: Put It All Back — Clean and Organised
Only when everything is dry should you move things back in. This is your chance to reorganise: clean pots stacked neatly, tools hung up, staging arranged for the season ahead. Return overwintering plants to their spots.
I always finish with a quick inventory: is the thermometer working? Is there enough potting compost? Do I need to replace any broken panes I spotted? A clean, organised greenhouse in October (or February) makes the whole next season smoother.
For more detailed product and method guidance, DIY Doctor’s greenhouse maintenance guide is a solid reference.
5 Mistakes to Avoid When Cleaning a Greenhouse
1. Using a pressure washer on glass. The force cracks panes and blows glazing clips out. Hose pressure is plenty.
2. Cleaning on a freezing day. Cold water on frost-cold glass can crack it, and disinfectants don’t work properly near freezing.
3. Using disinfectant at double strength. Stronger isn’t better — it damages surfaces, harms plants, and is unpleasant to breathe. Follow the dilution exactly.
4. Forgetting the gutters. Everyone cleans the glass and ignores the gutters. Blocked gutters cause more damp problems than dirty glass ever will.
5. Putting plants back while surfaces are still wet with disinfectant. Let everything dry completely. Residual disinfectant on staging can damage tender seedlings.
Frequently Asked Questions
How often should I clean my greenhouse?
Twice a year is the standard: a deep clean in late winter/early spring (February–March) before the growing season, and a second clean in autumn (September–October) after summer crops finish. A quick monthly tidy — sweeping debris and wiping staging — keeps things healthy between deep cleans.
Can I clean my greenhouse in winter?
You can, but pick a mild, frost-free day. Avoid washing glass when temperatures are near freezing, as the thermal shock can crack panes and disinfectants lose effectiveness in the cold. Late winter (February) is ideal — it’s the traditional main-cleaning window.
What is the best disinfectant for greenhouses?
A horticultural disinfectant such as Jeyes Fluid, used at the label dilution, is the standard choice and effective against the fungi, bacteria, and algae that trouble greenhouses. A mild bleach solution also works but must be rinsed thoroughly. Always ventilate well and wear gloves.
Should I remove plants before cleaning?
Yes, if at all possible. Plants get stressed by being moved, but they’re far more stressed by disinfectant fumes and cold draughts during cleaning. Move them outside on a mild day or cluster them in a sheltered corner covered with fleece, and keep cleaning chemicals well away from them.
Does cleaning the glass really make a difference to plants?
Absolutely — it’s one of the highest-impact jobs you can do. Dirty glass can block 30–40% of available light in winter. After a proper clean, you’ll notice seedlings grow stockier, germination improves, and the whole greenhouse feels brighter. Most growers who try it once never skip it again.
Final Thoughts
Knowing how to clean a greenhouse isn’t glamorous, but it’s the foundation everything else builds on. More light, fewer diseases, fewer pests, and a structure that’s inspected and sound — all from one weekend’s work, twice a year. My neglected-glass years cost me countless seedlings and a lot of frustration; don’t repeat my mistake.
Put the kettle on, pick an overcast Saturday, and give it a proper go. Come spring, your plants will thank you for it.
