Cleaning the Greenhouse for Winter
How to clean and sanitize the greenhouse without damaging the glazing or carrying this season's problems into the next.

By Angela Drake, BC Greenhouse Builders

By October, a greenhouse carries the story of the whole growing season. There may be soil beneath the benches, dried leaves tucked into corners, water marks on the glazing, and a few determined tomatoes still hanging on. It is evidence of a space that has been well loved.

A fall cleaning is one of the kindest things you can do for next year's garden. Removing old plant material takes away places where pests and disease can settle for winter. Washing the glazing allows for more of the season's limited light to make its way inside. Cleaning pots, tools, and growing surfaces gives spring seedlings a healthier place to begin.

It helps to think of this as two jobs. Cleaning removes soil, algae, dust, and plant residue. Sanitizing comes afterward and reduces the pests that remain. Give yourself a mild, sunny day, put on some music, and work through the greenhouse one area at a time.

Choose a Good Day and Make Space

Choose a dry day when doors and vents can remain open. Move healthy winter crops and tender plants to a protected spot while you work. Remove finished tomatoes, peppers, cucumbers, weeds, fallen leaves, and any fruit hidden behind pots. Healthy material can go into the compost, but plants showing disease or a serious pest problem should be disposed of separately to avoid further contamination.

Take out empty containers, trays, watering cans, plant supports, and tools. You will clean them before they return, but clearing the floor and benches first gives you room to see what needs attention. It also turns a large job into a satisfying reset.

Begin With a Dry Clean

Start at the top and work down. Remove cobwebs from corners and ledges, then brush or vacuum loose material from glazing bars, bolt tracks, vent screens, door thresholds, weather stripping, benches, and the floor. Pay special attention to narrow spaces where aphids, mites, eggs, or mold may be difficult to notice. Removing dry debris first keeps it from becoming muddy once the washing begins.

Clean for the Glazing You Have

Your cleaning method must be recommended for your glazing. For polycarbonate, begin with a lukewarm water rinse. Use mild soap and a soft cloth, wiping gently rather than scrubbing. Rinse again and dry with a soft cloth. Avoid abrasive pads, strong solvents, or anything that could scratch the surface or damage seals. Try not to get water in the panel flutes because it’s hard to get out later.

Glass and aluminum can be washed with warm soapy water before sanitizing. Choose a greenhouse disinfectant that is approved for the surface, and follow its label for dilution and instructions. Note how long it should stay on, if you need a well-ventilated area, and what protective equipment you need.

Wash What Goes Back Inside

Benches, shelves, pots, trays, plant labels, stakes, and hand tools can all carry soil and pests into another season. Replace cracked pots and worn trays that are difficult to clean properly.

Row covers deserve attention too. Wash them according to the manufacturer's instructions before placing them over winter crops. Starting with clean fabric helps avoid tucking aphids or mites into the warm, protected space you are creating for your plants.

Inspect Every Plant That Stays

Before putting plants back into the greenhouse, look closely at stems and both sides of the leaves. Remove the damaged leaves and isolate anything with an active pest problem until it has been treated. Sturdy leaves can be wiped gently with a soft, soapy cloth when appropriate for the plant. Fresh potting mix may be a good idea if the old soil is sour smelling or carrying fungus gnats.

Finish With the Winter Systems

Once everything is clean and dry, clear drainage grates, disconnect hoses where freezing is a concern, and check that doors and vents move freely. Clean circulation fans and test any heater, thermostat, or thermometer you rely on for winter. Then return only the plants and supplies that have earned their place back in your greenhouse. And now, when spring arrives, you can begin with clean pots and glazing, and knowing that the greenhouse is ready for spring’s rebirth.

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