Monty Don urges anyone with a greenhouse to do this one job before winter arrives

With the days growing shorter and temperatures beginning to tumble, it's time to start preparing our gardens for winter. And according to Monty Don, there's one job gardeners shouldn't overlook.

While you might be busy protecting tender plants from frost or clearing autumn leaves, the Gardeners' World presenter is encouraging anyone with a greenhouse to grab a sponge.

In a video shared on Instagram, Monty explains: "As we go into winter and you're using your greenhouse for storage, it's really important to clean the glass thoroughly."

It's a task that's easy to put off, particularly when the greenhouse is being used to store pots, tools and gardening equipment. But removing accumulated dirt and grime can make a real difference during the darker months.

Why should you clean greenhouse glass before winter?

During spring and summer, greenhouse panes can accumulate dirt, algae and other deposits, particularly in damp or shaded areas.

While a little grime might seem harmless, it can reduce the amount of natural light reaching plants inside. This becomes especially important during autumn and winter, when daylight hours are shorter and the sun sits lower in the sky.

For gardeners overwintering tender plants or growing winter crops, Monty says keeping the glass clean "will maximise available light throughout the winter months".

He adds that even if you're just using your greenhouse for storage, a thorough autumn clean will "help resist disease harbouring over winter".

How to clean your greenhouse glass

Before getting started, move any pots, trays or gardening equipment that might get in the way. This is also a good opportunity to clear away fallen leaves, old compost and plant debris.

Mix warm water with a few drops of washing-up liquid. With a sponge, cloth, or – Monty's cleaning tool of choice – a Squeegee, gently wash the greenhouse panes to remove accumulated dirt and algae. For stubborn marks, a little mild detergent may help, provided it's suitable for your greenhouse's glazing material.

Pay particular attention to corners and window frames, where grime can build up unnoticed.

Rinse away any cleaning residue with clean water and allow the surfaces to dry.

If you're cleaning the inside of your greenhouse, take care to protect any plants from cleaning products and avoid using harsh chemicals that could damage foliage or leave unwanted residues.

It's also worth checking the manufacturer's cleaning recommendations, particularly if your greenhouse has polycarbonate panels rather than traditional glass.

For safety, avoid standing on greenhouse structures or attempting to reach high panes from an unstable ladder.

What else should you do to prepare your greenhouse for winter?

Once the glass is sparkling, there are a few other simple jobs worth tackling before the coldest weather arrives.

Check doors, windows and vents for damage, and make sure they're opening and closing properly. Repairing broken panes or damaged seals can help protect vulnerable plants from cold draughts.

Remove any dead or diseased plant material, clean empty pots and seed trays, and tidy up shelves to discourage pests from settling in over winter.

If you're overwintering tender plants, consider whether additional protection, such as horticultural fleece or suitable greenhouse insulation, might be needed.

However, don't forget about ventilation. Even during winter, greenhouses can become humid, so allowing fresh air to circulate when conditions permit can help reduce condensation and fungal problems.