How to Clean a Greenhouse

The best time is autumn, after the last crops are cleared, or late winter before seed sowing starts. The greenhouse is emptiest then, and cleaning removes the overwintering eggs and spores of pests and diseases such as red spider mite, whitefly and grey mould.

Choose a mild, dry, still day so that plants you move outside aren't damaged by frost, and the greenhouse can dry out afterwards.

Move plants, pots, trays and tools outside, and cover tender plants with fleece. Sweep out soil, leaves and plant debris from the floor and staging. Remove any old shading wash or shade netting, and take down bubble insulation if you're replacing it.

Use warm water with a little washing-up liquid or a horticultural disinfectant, and a soft brush or sponge on a pole. Work from the top down, inside and out. A plastic plant label is handy for scraping out the algae and dirt that collect where panes overlap – it's often the dirtiest part of the glass and blocks a lot of light.

Rinse thoroughly with a hose on a gentle setting, avoiding high pressure, which can dislodge panes and glazing clips. For polycarbonate panels, use only a soft cloth and mild soapy water; abrasive cleaners and solvents scratch and cloud them.

Scrub the frame, glazing bars and door runners with the same solution and an old toothbrush for the grooves. Clean the greenhouse gutters and downpipe so rainwater can flow to your water butt, and clean the water butt itself if it smells or is full of sludge.

Wash the staging, shelving and benches, getting into the corners and slats. Wooden staging can be scrubbed with a horticultural disinfectant and left to dry fully.

Old pots and seed trays can carry diseases that affect seedlings. Wash them in warm soapy water with a stiff brush to remove soil and algae, then soak them in a horticultural disinfectant if you're concerned about disease, rinse and stack them to dry. Clean secateurs and tools and wipe them with a little oil.

Leave the door and vents open for a day or two after cleaning so everything dries completely before plants go back in. A clean, dry greenhouse with good airflow is much less likely to suffer from grey mould over winter. Fit fresh bubble insulation if you use it, leaving the vents uncovered.

Many window cleaners using water-fed poles will clean the outside of greenhouse glass, and some will also do the inside if it's empty. Conservatory roof cleaning specialists can often clean large greenhouses and orangeries. Our guide to cleaning conservatory roofs covers similar techniques for glass and polycarbonate roofs.

A full clean once a year is the big job, but a little attention during the season helps plants thrive. Sweep the floor and remove dead leaves and fallen fruit weekly, as they harbour pests and grey mould. Wipe the inside of the glass if condensation leaves a film, and check gutters after heavy rain.

In hot weather, many gardeners apply a temporary shading wash to the outside of the glass to stop plants scorching; remove it in autumn so winter light can get in. Keep an eye out for aphids, whitefly and red spider mite under leaves, and clean pots and trays before reusing them for new sowings.