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A well-maintained polycarbonate greenhouse is a better growing environment than a neglected one — more light reaching the plants, better insulation performance from properly sealed panels, and a healthier internal environment that reduces disease pressure on crops. None of this requires significant effort or specialist equipment. The maintenance schedule for a KLASIKA or BALTIC LT greenhouse is straightforward, seasonal, and achievable in a few hours spread across the year.
This guide covers everything: what to clean and when, which products to use, what to avoid, how to manage the seasonal tasks that make the biggest difference to growing performance, and how to keep the frame and panels looking and performing as intended across the full service life of the greenhouse.
Greenhouse maintenance is not separate from greenhouse growing — it is part of it. Algae and mineral deposits on the outside of the panels reduce light transmission. Debris and pest harbourage points inside the greenhouse carry disease from one season to the next. A door that sticks or a vent that does not open fully is a ventilation and access problem that compounds across the season.
The maintenance tasks in this guide are not optional extras for the fastidious — they are the housekeeping that keeps a greenhouse operating as designed. The good news is that none of them are onerous. A polycarbonate greenhouse with a galvanised steel frame requires substantially less maintenance than its glass or timber equivalents — no repainting, no reglazing, no re-sealing of timber joints. The maintenance that is required is cleaning, seasonal inspection, and the right product choices when growing pressure demands them.
The cleaning protocol for Brett Martin twin-wall polycarbonate panels is simple: lukewarm water, mild liquid soap, and a soft cloth or microfibre sponge. This is the complete list of materials you need for routine panel cleaning. Nothing more elaborate is required or beneficial.
Mild soap — washing-up liquid at normal dilution is ideal — breaks down surface deposits of algae, mineral residue, and dust without leaving a residue that attracts further soiling. Microfibre cloths are the safest cloth material for polycarbonate surfaces: they are soft enough to avoid any scratching risk and absorbent enough to pick up loosened surface material efficiently.
Rinse thoroughly with clean water after cleaning. Residual soap on the panel surface will accelerate the re-soiling of the surface as airborne dust adheres to it.
Pressure washers. The combination of high pressure and a concentrated water jet damages polycarbonate panel surfaces in two ways: it can mechanically scratch and abrade the UV-protective outer layer, and it can force water under pressure into the panel end channels and between the glazing bar cap and the panel edge, compromising the internal structure of the multi-wall panel. Pressure washers are not appropriate for polycarbonate greenhouse cleaning under any circumstances.
Abrasive pads and scouring compounds. Polycarbonate is softer than glass and will scratch under abrasive contact. Even what feels like a gentle scouring pad will produce fine surface scratches that accumulate over cleaning sessions into a visible haze that reduces light transmission and optical clarity. Use soft cloths only.
Solvent-based cleaners. Acetone, white spirit, turpentine, methylated spirit, and similar solvents attack the polycarbonate polymer directly — they do not clean the surface, they dissolve it. The damage is immediate and irreversible. Check the label of any cleaning product before use: if it contains solvents, do not use it on polycarbonate panels.
Ammonia-based cleaners. Many multi-surface household cleaners and glass cleaning sprays contain ammonia. Ammonia damages polycarbonate, causing stress crazing and surface degradation over time. Read labels carefully. Standard glass cleaners are not safe for polycarbonate.
Wire brushes or steel wool. Under no circumstances. These will produce deep, permanent scratching.
The concentrated disinfection product available for KLASIKA greenhouses is a broad-spectrum solution effective against bacteria, viruses, and fungi. It is specifically formulated for greenhouse use — diluted to working concentration, it is applied to all internal surfaces at the deep clean stages of the maintenance schedule.
Its primary role is sanitation between growing seasons: removing the disease inoculum that accumulates on frame members, staging, bed edges, and internal floor surfaces during the growing season and that would, if left in place, provide the starting point for fungal and bacterial disease pressure on the following season’s crops. Botrytis (grey mould), powdery mildew, and fusarium are among the pathogens that persist on greenhouse surfaces and infect new crops at the start of the season.
Dilute according to the product instructions. Apply to all internal surfaces — frame members, bed edges, path surfaces, staging, the internal face of panels — after removing all plant material and growing media from the greenhouse. Allow to work for the specified contact time, then rinse. The greenhouse is then ready for the following season with the disease pressure from the previous one removed.
The universal surface cleaner is the product for external panel cleaning and for any surface within or around the greenhouse where organic growth — algae, moss, lichen — has established. It is suitable for polycarbonate, glass, film, metal, paving, and most garden surfaces, making it a versatile product for the full range of greenhouse and garden maintenance tasks.
For greenhouse panels, dilute to the appropriate concentration for organic growth removal and apply with a soft cloth or garden sprayer to affected areas. Allow the solution to work for a few minutes to break down the organic material, then wipe or rinse off. Thorough rinsing removes both the dissolved organic material and the cleaning solution itself.
This product is also effective for cleaning guttering, downpipes, base rails, and the exterior surfaces of the greenhouse frame — areas that accumulate organic growth and mineral deposits over time and benefit from periodic cleaning beyond the panel surfaces alone.
The greenhouse shading solution is applied to the exterior surface of the panels during the hottest months to reduce solar gain and prevent the overheating that can damage crops and growing conditions in a closed greenhouse in full summer sun.
It is applied by diluting according to the instructions and applying to the exterior panel surface — typically by brush or garden sprayer, working along panel runs from one end of the greenhouse to the other. When dry, it forms a light, translucent coating that reduces solar gain without completely blocking light. It is water-resistant once dry but washes off cleanly in autumn with a standard panel wash when it is no longer needed.
The shading solution is compatible with Brett Martin polycarbonate panels and does not damage the UV layer or panel structure. It is the recommended shading approach specifically because it applies to the outside of the panels — reducing solar gain before it enters the greenhouse — rather than shading from inside, where the heat has already been admitted.
Spring is the most important maintenance window of the year. The work done in March and April determines the quality of the growing environment for the entire season ahead.
External panel clean. Winter deposits — algae from the wet months, mineral residue from rain, moss around panel edges and base rails — will have accumulated on the exterior surfaces. Clean the panels thoroughly using the universal surface cleaner diluted to the organic growth concentration, then rinse with clean water and wipe down with a soft cloth. A clean start to the season maximises light transmission from the first sowings.
Pay particular attention to the base sections and panel edges, where algae growth tends to be heaviest. The junction between the bottom of the panels and the glazing bar base is a point where debris accumulates and organic growth establishes — clean this thoroughly with a cloth rather than relying on rinse alone.
Internal deep clean. If the full internal disinfection was not carried out at the end of the previous season (see Autumn section), carry it out now before any new crops are planted. Apply the concentrated disinfection solution to all internal surfaces, observe the contact time, and rinse. Let the greenhouse dry and ventilate thoroughly before introducing any plant material.
Structural inspection. Walk around the outside of the greenhouse and check:
Vent opener check. If you use automatic wax-cylinder vent openers, test them in early spring before they are needed. The wax cylinder should push the vent open when the opener is held in a warm hand and close when cooled. Openers that are not functioning should be replaced before the temperature-critical period begins.
Panel sealing check. Inspect the aluminium tape on the top edges of all panels. Tape that has lifted or is peeling should be replaced — this is the point of entry for water into the panel channels from above, and an intact top seal is essential for panel longevity.
The summer maintenance tasks are primarily about managing the heat and humidity that a productive greenhouse generates in warm months.
Ventilation management. A closed greenhouse in direct summer sun can reach damaging temperatures within an hour. Roof vents should be open from mid-morning on any day where outdoor temperature is above 18°C and sun is present. If you use automatic vent openers, they manage this passively — the wax cylinder opens the vent as temperature rises and closes it as it falls. Manual vents need daily attention.
Door management plays an equal role in summer ventilation. Opening the greenhouse door on hot days — in addition to roof vents — creates the through-draught that drops internal temperature most effectively. A base-level vent or louvre at one end and roof vents at the other creates a temperature-driven convection current that is the most efficient natural ventilation pattern.
Shading solution application. From late May onwards — when daytime temperatures are consistently warm and the sun is at its highest angle — apply the greenhouse shading solution to the exterior of the panels as described above. Early application, before significant overheating events have occurred, is better than reactive application after the first scorching event of the season.
The shading solution is most needed on the roof panels and the south-facing side panels. North-facing side panels and end walls receive less direct sun and typically do not need shading treatment.
Regular panel wipe-down. In summer, internal condensation and the humidity of a productive growing environment deposit films on the inner panel faces that reduce light transmission and encourage algae growth. A wipe-down of accessible internal panel surfaces every four to six weeks with a soft cloth and mild soapy water maintains light transmission through the peak growing months.
Guttering and drainage. Summer thunderstorms can produce intense rainfall over short periods. Check that guttering is clear and that downpipes are flowing freely after any heavy rainfall event. Blocked guttering produces overflow that runs down the outside of the greenhouse walls and accumulates at the base — not immediately damaging, but creating conditions that encourage algae growth at the base rail level.
Pest and disease monitoring. The warm, humid interior of a greenhouse in summer is ideal for red spider mite, whitefly, and botrytis. Regular inspection of plant foliage — undersides of leaves particularly — in June, July, and August gives early warning of pest establishment that is far easier to manage when caught early than when an infestation is established. Good ventilation is the primary preventive measure for botrytis; sticky traps near the door help monitor flying pest pressure.
Autumn maintenance is the most important single maintenance investment you can make for the following year’s growing performance. A properly closed-down greenhouse starts the next season with clean surfaces, intact seals, and no disease carryover from the previous growing year.
Remove all plant material. Clear the greenhouse of all growing crops before the first hard frost. This includes removing all crop residues — fallen leaves, spent stems, root balls — from beds, staging, and floor surfaces. Crop debris left in the greenhouse over winter is the primary reservoir of disease inoculum that infects the following season’s plantings.
Remove and clean staging and shelving. Staging and shelving accumulate soil, plant debris, and the early stages of fungal growth through the season. Remove them from the greenhouse, clean with the universal surface cleaner, and allow to dry before returning or storing.
Shading solution removal. The greenhouse shading solution washes off with a standard external panel clean — no special removal product is needed. Carry out the autumn external panel wash, which removes both the shading solution and the organic growth that has accumulated during the summer months.
Internal disinfection. This is the most important step of the autumn close-down. With all plant material and equipment removed, apply the concentrated greenhouse disinfection solution to all internal surfaces: frame members, panel inner faces, bed edges, staging surfaces, floor, and path. Pay particular attention to junctions and corners where debris accumulates and fungal growth establishes most readily.
Dilute according to the product instructions, apply thoroughly, allow the specified contact time, and rinse completely. Ventilate the greenhouse fully after rinsing and allow to dry before any equipment is returned or overwintering plants are introduced.
A greenhouse that has been thoroughly disinfected in autumn starts the following March with disease pressure at its lowest point of the cycle — and crops that start in a clean environment establish faster and perform better throughout their season.
External panel clean. Follow the same protocol as the spring external clean: universal surface cleaner at organic growth concentration, applied with a soft cloth or sprayer, followed by thorough rinsing. The autumn clean removes the summer’s accumulated deposits and the shading solution coating.
Panel and seal inspection. Repeat the structural inspection from the spring checklist:
Overwintering plant preparation. If the greenhouse is being used for overwintering tender plants — pelargoniums, fuchsias, citrus, Mediterranean herbs — introduce them after the disinfection and drying process is complete, not before. Introducing plants into a freshly disinfected greenhouse gives them the cleanest possible starting environment for the winter months.
Winter maintenance is the lightest in the calendar — the greenhouse is doing relatively little work and the tasks are primarily monitoring and occasional intervention rather than active maintenance.
Snow clearance. In the event of significant snow accumulation on the roof, remove it if it is practical to do so safely. The galvanised steel frame is designed to carry structural loads including snow, and the Brett Martin polycarbonate panels have good load-bearing properties — this is not an emergency action required after every snowfall. For heavy, prolonged snow accumulation, particularly on the roof, clearing it reduces the load the structure is carrying and is worth doing if you can do it safely.
Do not use tools that could damage the panel surface. A soft-bristled brush extended to reach the roof panels is the appropriate tool. Do not apply pressure directly to the panels or attempt to break ice off the surface.
Ventilation in mild spells. In mild winter weather — above 10°C — brief ventilation of the greenhouse on dry days prevents the stale, humid air that encourages fungal growth on overwintering plants from accumulating. Even fifteen minutes of open door and open vent on a mild, dry winter day makes a meaningful difference to the internal air quality.
Heater check. If you use a frost-stat heater for minimum temperature control, check that it is operating correctly at the beginning of the coldest months. The consequences of heater failure on a -5°C night are immediate and potentially devastating for overwintering plants. A simple test — confirming the heater activates when the thermostat is set above the current temperature — takes two minutes and is worth doing in November before the cold weather arrives.
Condensation on panels. Internal condensation in winter is normal and expected — it is the result of temperature differential between inside and outside the greenhouse. It is not a sign of panel failure. The twin-wall insulation of the polycarbonate panels means the inner face is warmer than in a single-glazed structure, reducing condensation compared to glass, but not eliminating it entirely. Adequate ventilation — even winter ventilation — is the primary management tool.
The galvanised steel frame of a KLASIKA or BALTIC LT greenhouse is designed to be maintenance-free in normal service. The Z275 zinc coating provides decades of corrosion protection without any painting, re-coating, or treatment. There is nothing that needs doing to the frame annually.
The only relevant annual check is a visual inspection of the frame at ground level — the arch feet and base rail sections that are in contact with soil or have the least air circulation around them. Look for any area where the zinc coating has been physically damaged (a tool scratch, an impact mark, an abrasion) and where the underlying steel is exposed. If you find such a point, a small application of zinc-rich cold galvanising compound — available from hardware suppliers — protects the exposed steel and prevents any corrosion from initiating. This is an occasional repair task rather than a routine maintenance requirement.
Surface discolouration of the zinc coating — a dull, sometimes mottled appearance that develops on galvanised steel after outdoor exposure — is normal and cosmetic. It is not a sign of failure; it is the natural weathering of the zinc surface and does not indicate any loss of protective function.
The door hinges on KLASIKA and BALTIC LT greenhouses require occasional lubrication — not annually, but whenever a door begins to develop any stiffness or squeak in its movement. A light application of general-purpose lubricating oil to hinge pivot points and, if applicable, any sliding track system is all that is needed. Do not use heavy grease, which attracts and retains dirt and provides no better lubrication than light oil.
If a door develops binding — resistance to opening or closing that was not present initially — check the alignment of the door frame rather than assuming the hinges need adjustment. Binding in a previously smooth door usually indicates that the frame geometry has changed slightly — often the result of the ground having settled unevenly at the arch feet — and a minor adjustment to the anchor point of the problematic arch typically restores door operation.
Light transmission is the performance characteristic most directly affected by maintenance quality. A greenhouse with panels transmitting 80% of available light, fouled by algae and mineral deposits to the point of effective transmission of 65%, is a meaningfully worse growing environment — the equivalent of reducing the growing day by an hour or more.
The practices that maintain peak light transmission are:
Cleaning frequency. Annual cleaning is a minimum. In areas with significant rainfall, soft water, and minimal algae pressure — drier parts of the country, elevated positions — annual spring and autumn cleans are sufficient. In humid areas, wetter gardens, and positions with nearby trees that cast deposits, a summer clean in addition to the spring and autumn programme maintains light transmission at its best.
Correct products. The universal surface cleaner removes both inorganic mineral deposits and organic algae growth that a simple soap-and-water wash cannot fully address. Use it at least once per year, at the spring clean, and additionally whenever algae growth is visible on the exterior panel surfaces.
Panel end cap integrity. Algae growing inside the panel channels — between the two faces of the twin-wall structure — cannot be removed without replacing the panel. It presents as a green or grey internal discolouration visible through the panel face that is not on the surface and therefore not cleanable. It is entirely prevented by ensuring the top panel edges are sealed with intact aluminium tape and the bottom edges have functioning breathable filter caps. Checking these at spring and autumn inspections and replacing any that are damaged is the maintenance action that prevents internal algae growth from ever becoming a problem.
| Season | Task | Product |
|---|---|---|
| Early spring (March) | External panel clean | Universal surface cleaner |
| Early spring (March) | Internal disinfection (if not done in autumn) | Concentrated greenhouse disinfection solution |
| Early spring (March) | Structural inspection, end cap check, tape check | — |
| Early spring (March) | Vent opener function test | — |
| Late May onwards | Apply shading solution (south panels and roof) | Greenhouse shading solution |
| Every 4–6 weeks in season | Internal panel wipe-down | Mild soap and water |
| After summer ends (Sept–Oct) | Shading solution removal + full external panel clean | Universal surface cleaner |
| Autumn (October–November) | Remove all crop material and equipment | — |
| Autumn (October–November) | Internal deep disinfection | Concentrated greenhouse disinfection solution |
| Autumn (October–November) | Panel and seal inspection, end cap check | — |
| Winter as needed | Snow clearance (heavy accumulation) | Soft brush |
| Winter (November) | Heater function check | — |
| Winter as needed | Brief ventilation in mild spells | — |
All maintenance products mentioned are available from KLASIKA greenhouse retailers:
Concentrated greenhouse disinfection solution — kills bacteria, viruses, and fungi on greenhouse surfaces. For use at seasonal deep cleans and when disease pressure is a concern.
Universal concentrated surface cleaner — for polycarbonate panels, fences, guttering, paving, and outdoor furniture. The core cleaning product for external greenhouse maintenance.
Greenhouse shading solution — for application to polycarbonate, glass, or film surfaces. Reduces solar gain in summer, washes off cleanly in autumn.
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